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Exam CramCCNA Practice Questions (Exam 640-802) Third Edition Jeremy Cora, CCIE No. 11727
Contents at a GlancePart I: ICND1 CHAPTER 1: Operation of Data Networks CHAPTER 2: Switching Foundations CHAPTER 3: Basic IP Services CHAPTER 4: IOS and Routing Foundations CHAPTER 5: Wireless and Network Security Concepts CHAPTER 6: Basic WAN ConnectivityPart II: ICND2 CHAPTER 7: Advanced Switching Concepts CHAPTER 8: Subnetting, VLSM, and IPv6 CHAPTER 9: Advanced Routing Configuration CHAPTER 10: Access Lists and Network Address Translation CHAPTER 11: Frame Relay, PPP, and VPN Connectivity APPENDIX: Whats on the CD-ROMTable of ContentsAbout the AuthorIntroductionPart I: ICND1Chapter 1: Operation of Data Networks Quick Answer Key Answers and ExplanationsChapter 2: Switching Foundations Quick Answer Key Answers and ExplanationsChapter 3: Basic IP Services Quick Answer Key Answers and ExplanationsChapter 4: IOS and Routing Foundations Quick Answer Key Answers and ExplanationsChapter 5: Wireless and Network Security Concepts Quick Answer Key Answers and ExplanationsChapter 6: Basic WAN Connectivity Quick Answer Key Answers and ExplanationsPart II: ICND2
Chapter 7: Advanced Switching Concepts Quick Answer Key Answers and ExplanationsChapter 8: Subnetting, VLSM, and IPv6 Quick Answer Key Answers and ExplanationsChapter 9: Advanced Routing Configuration Quick Answer Key Answers and ExplanationsChapter 10: Access Lists and Network Address Translation Quick Answer Key Answers and ExplanationsChapter 11: Frame Relay, PPP, and VPN Connectivity Quick Answer Key Answers and ExplanationsAppendix: Whats on the CD-ROM Multiple Test Modes Attention to Exam Objectives Installing the CD Creating a Shortcut to the MeasureUp Practice Tests Technical SupportAbout the AuthorJeremy Cioara, CCIE No. 11727,Part I: ICND1Chapter 1 Operation of Data NetworksChapter 2 Switching FoundationsChapter 3 Basic IP ServicesChapter 4 IOS and Routing FoundationsChapter 5 Wireless and Network Security ConceptsChapter 6 Basic WAN ConnectivityChapter 1. Operation of DataNetworks
This chapter covers the following CCNA objectives that fall under the contentarea, Describe how a network works: Describe the purpose and functions of various network devices. Select the components required to meet a network specification. Use the OSI and TCP/IP models and their associated protocols to explain how data flows in a network. Describe common networked applications including web applications. Describe the purpose and basic operation of the protocols in the OSI and TCP models. Describe the impact of applications (Voice over IP and Video over IP) on a network. Interpret network diagrams. Determine the path between two hosts across a network. Describe the components required for network and Internet communications. Identify and correct common network problems at Layers 1, 2, 3, and 7 using a layered model approach. Differentiate between LAN/WAN operation and features.1. You are a network technician at Bubbles, Inc. Your newly appointed trainee is troubleshooting a connectivity problem on the network and would like to test application layer connectivity between devices. What command would you use? 1. A. ping 2. B. telnet 3. C. traceroute 4. D. verify 5. E. traceQuick Answer: 16Detailed Answer: 172. You are connecting a laptop to a Cisco router to configure it for the first time. After opening your terminal program and selecting COM1, you are prompted for the port settings. What settings should you use? 1. A. 9600bps, 8 data bits, no parity, 1 stop bit, hardware flow control 2. B. 9600bps, 8 data bits, no parity, 1 stop bit, no flow control 3. C. 56000bps, 8 data bits, no parity, 1 stop bit, hardware flow control 4. D. 56000bps, 8 data bits, no parity, 1 stop bit, no flow control
Quick Answer: 16Detailed Answer: 173. Which of the following is a security concern when configuring a device using Telnet? 1. A. All communication is sent in clear text. 2. B. Passwords are sent using reversible encryption. 3. C. Passwords cannot be changed in a Telnet session. 4. D. Passwords are not used during a Telnet session.Quick Answer: 16Detailed Answer: 174. You are attempting to test telnet connectivity to a Cisco router in your companys lab environment, but are unable to create a session. What should you do to resolve the problem? 1. A. Use a straight-through cable to connect your computers COM port to the routers console port. 2. B. Use a rollover cable to connect your computers COM port to the routers console port. 3. C. Use a straight-through cable to connect your computers COM port to the routers Ethernet port. 4. D. Use a crossover cable to connect your computers Ethernet port to the routers Ethernet port. 5. E. Use a rollover cable to connect your computers Ethernet port to the routers Ethernet port. 6. F. Use a straight-through cable to connect your computers Ethernet port to the routers Ethernet port.Quick Answer: 16Detailed Answer: 175. Which of the following is a valid benefit of using a hub in an enterprise network? 1. A. A network hub could be used to monitor network traffic from multiple sources using a packet sniffer or IDS/IPS appliance. 2. B. Because it is hardware-based, a hub can transmit traffic with less latency than a network switch. 3. C. A hub provides a better throughput for steady, low-bandwidth streams of traffic such as Voice over IP (VoIP) or Video over IP (VIP). 4. D. A hub provides dedicated bandwidth on a per-port basis.Quick Answer: 16Detailed Answer: 17
6. You are preparing to discuss the foundations of network communication with a junior administrator at your company. How would you describe the characteristics of TFTP using the OSI model? 1. A. TFTP is a transport layer protocol that transmits using TCP port 21. 2. B. TFTP is an application layer protocol that transmits over the transport layer protocol TCP using port 21. 3. C. TFTP is an application layer protocol that transmits over the transport layer protocol UDP using port 69. 4. D. TFTP is a network layer protocol that transmits using UDP port 69.Quick Answer: 16Detailed Answer: 177. You are using Microsoft Internet Explorer on a PC to access the Cisco website (www.cisco.com). What source port will your PC use for communication? 1. A. UDP port 80. 2. B. TCP port 80. 3. C. The port will be randomly assigned by the operating system. 4. D. Any TCP port under 1024.Quick Answer: 16Detailed Answer: 178. You are a network consultant for a small, 20-user company. The company has purchased a new building and would like you to design a network infrastructure using Cisco equipment. The company will be using a cable modem Internet connection, multiple mobile laptops, and 15 stationary desktop PCs. The company would also like VPN connectivity remotely to the office. What are the most likely network components you will use? (Choose three.) 1. A. Cisco switch 2. B. Cisco router 3. C. VLANs 4. D. ASA firewall 5. E. Cisco Wireless Access Point 6. F. Cisco IPS SensorQuick Answer: 16Detailed Answer: 189. An interface capable of sending at a T1 speed would be transmitting data at which of the following? 1. A. 1.544 Mbps
2. B. 1.544 MBps 3. C. 1.544 Gbps 4. D. 1.544 GBpsQuick Answer: 16Detailed Answer: 1810. Routing decisions are made at which layer of the OSI model? 1. A. Application 2. B. Transport 3. C. Session 4. D. Data Link 5. E. NetworkQuick Answer: 16Detailed Answer: 1811. Which of the following protocols operate solely at Layer 2 of the OSI model? (Choose three.) 1. A. 802.3 MAC 2. B. IP 3. C. HDLC 4. D. PPP 5. E. ISDN 6. F. TCPQuick Answer: 16Detailed Answer: 1812. Which of the following are common network applications? (Choose three.) 1. A. Graphics creation 2. B. Email 3. C. Spreadsheets 4. D. Instant messaging 5. E. Database 6. F. Word processingQuick Answer: 16Detailed Answer: 1813. What is the primary purpose of a router? (Choose two.) 1. A. To provide an intermediary device where network signals are transmitted
from one device to another 2. B. To control broadcast and multicast traffic from flooding through multiple networks 3. C. To interconnect networks and provide the best path between them 4. D. To protect networks using firewall capabilities implemented by using access listsQuick Answer: 16Detailed Answer: 1814. Refer to Figure 1.1. HostA wants to communicate with ServerB. What destination MAC address will be in the header of the packet at position A (as notated in Figure 1.1)?Figure 1.1. Network diagram. 1. A. The MAC address of HostA 2. B. The MAC address of SwitchA 3. C. The MAC address of RouterA 4. D. The MAC address of RouterB 5. E. The MAC address of SwitchB 6. F. The MAC address of ServerBQuick Answer: 16Detailed Answer: 1815. Refer to Figure 1.1. HostA wants to communicate with ServerB. What destination IP address will be in the header of the packet at position A (as notated in Figure 1.1)? 1. A. The IP address of HostA 2. B. The IP address of SwitchA 3. C. The IP address of RouterA 4. D. The IP address of RouterB
5. E. The IP address of SwitchB 6. F. The IP address of ServerBQuick Answer: 16Detailed Answer: 1916. Refer to Figure 1.1. HostA wants to communicate with ServerB. What source MAC address will be in the header of the packet at position B (as notated in Figure 1.1)? 1. A. The MAC address of HostA 2. B. The MAC address of SwitchA 3. C. The MAC address of RouterA 4. D. The MAC address of RouterB 5. E. The MAC address of SwitchB 6. F. The MAC address of ServerBQuick Answer: 16Detailed Answer: 1917. Refer to Figure 1.2. HostA is unable to communicate with ServerB. Based on the information given in the Figure 1.2, what is the most likely cause of the problem?Figure 1.2. Network diagram. 1. A. HostA and ServerB are on different subnets. 2. B. HostA and ServerB are on the same subnet. 3. C. RouterA or RouterB has an access list, which prevents HostA from reaching ServerB. 4. D. Crossover cables should be replaced with straight-through cables.Quick Answer: 16Detailed Answer: 19
18. Which of the following are valid fields in a TCP header? (Choose four.) 1. A. Sequence number 2. B. Source IP address 3. C. Checksum 4. D. Acknowledgement number 5. E. Destination MAC address 6. F. Destination portQuick Answer: 16Detailed Answer: 1919. Refer to Figure 1.3. HostA issues a ping request to HostB. Which of the following outputs would accuratelyreflect the contents of the ARP table on HostA?Figure 1.3. Network diagram. 1. A. C:> arp -a Interface: 192. 168. 1.10 on Interface 0x10000003 Internet Address Physical Address Type 192.168.1.1 00-0c-85-4c-05-00 dynamic 2. B. C:> arp -a Interface: 192. 168. 1.10 on Interface 0x10000003 Internet Address Physical Address Type
192.168.1.1 00-0c-85-4c-05-00 dynamic 192.168.2.1 00-0c-85-4c-05-01 dynamic 192.168.2.10 00-b1-33-df-5e-11 dynamic 1. C. C:> arp -a Interface: 192 .168. 1.10 on Interface 0x10000003 Internet Address Physical Address Type 192.168.1.1 00-0c-85-4c-05-00 dynamic 192.168.2.10 00-b1-33-df-5e-11 dynamic 2. D. C:> arp -a Interface: 192. 168. 1.10 on Interface 0x10000003 Internet Address Physical Address Type 192. 168. 1.11 00-0a-11-3c-34-01 dynamicQuick Answer: 16Detailed Answer: 1920. You are troubleshooting network connectivity issues between a Microsoft Windows client and a server. The servers IP address recently changed and you want to clear the clients ARP table. What command will accomplish this? 1. A. arp -clear 2. B. arp -a 3. C. arp –c all 4. D. arp –d *Quick Answer: 16Detailed Answer: 1921. Which of the following commands would allow a network client to test connectivity to a destination device and verify the current delay for each router traversed while making the connection? 1. A. ping 2. B. test 3. C. tracert 4. D. telnet 5. E. ssh –h -dQuick Answer: 16Detailed Answer: 19
22. Refer to Figure 1.4. HostA just transmitted a certain amount of data to HostB. What does HostBs response indicate?Figure 1.4. Network diagram. 1. A. HostBs response is a retransmission of data requested by HostA. 2. B. HostB has indicated that a portion of HostAs transmission was not received and needs to be retransmitted. 3. C. HostBs response indicates the TCP session will now close. 4. D. HostBs response is normal and expected. Network communication will continue unhindered.Quick Answer: 16Detailed Answer: 2023. The following is a list of network functions. Enter the appropriate letter to match the network function to the corresponding OSI layer. A = Data link layer B = Network layer 1. A. ______Provides error detection 2. B. ______Routes data packets 3. C. ______Finds the best path to use when delivering data 4. D. ______Provides logical addressing 5. E. ______Provides physical addressing 6. F. ______Defines how data is formatted for transmissionQuick Answer: 16Detailed Answer: 2024. Match the correct term to the corresponding OSI layer. A = Physical layer B = Data link layer C = Network layer D = Transport layer
1. A. ______ Segments 2. B. ______ Frames 3. C. ______ Bits 4. D. ______ PacketsQuick Answer: 16Detailed Answer: 2025. The application layer of the TCP/IP stack corresponds to which of the following three OSI model layers? (Choose three.) 1. A. ______ Physical 2. B. ______ Transport 3. C. ______ Data link 4. D. ______ Segments 5. E. ______ Presentation 6. F. ______ Session 7. G. ______ Network 8. H. ______ ApplicationQuick Answer: 16Detailed Answer: 2126. A host is assigned the IP address 10.5.62.173/27. An application on the host attempts to contact a server with the IP address 10.5.62.158/27. What is the next step in the process of network communication? 1. A. The host will send an ARP message directly to the destination server to obtain its MAC address. 2. B. The host will contact the IP address of its default gateway to find the MAC address for the destination server. 3. C. The host will send an ARP broadcast to find the MAC address of its default gateway. 4. D. The host will send an ARP broadcast to find the MAC address of the destination server.Quick Answer: 16Detailed Answer: 2127. Users on a specific network segment in your organization are complaining that they cannot reach the Internet. While working through the troubleshooting process, you discover that all the ports connecting to the PCs in the segment have been set to auto-negotiate speed and duplex. You also gather information from one of the end-user workstations; this information is shown in Figure 1.5. What is the most likely cause of the problem?
Figure 1.5. Command prompt output. 1. A. All host and server connections in the network should have speed and duplex hard coded. 2. B. The connectivity problems are related to an IP addressing issue. 3. C. The default gateway could be blocking ICMP ping traffic. 4. D. All ports should be set for 10Mbps, half-duplex connections for testing purposes.Quick Answer: 16Detailed Answer: 2228. Refer to Figure 1.6. HostA has just sent a ping request to HostB. Based on the information given in Figure 1.6, how will the switch respond?Figure 1.6. Network diagram.
1. A. The switch will forward the frame out FA0/2. 2. B. The switch will flood the frame out all ports. 3. C. The switch will multicast the frame only to unknown ports. 4. D. The switch will flood the frame out all ports except FA0/1.Quick Answer: 16Detailed Answer: 22 Share29. When data is being encapsulated, the last piece of information to be added is the _________. 1. A. TCP source and destination port 2. B. Destination IP address 3. C. Source IP address 4. D. FCS
About This Book How to Use This Book How This Book Is Organized Book I: Networking Basics Book II: Building a Network Book III: Network Administration and Security Book IV: TCP/IP and the Internet Book V: Wireless Networking Book VI: Mobile Networking Book VII: Windows Server 2008 R2 Reference Book VIII: Using Other Windows Servers Book IX: Managing Linux Systems Icons Used in This Book Where to Go from HereBook IChapter 1: Understanding Networks What Is a Network? Network building blocks Why bother? Of Clients and Servers Dedicated Servers and Peers Networks Big and Small Network Topology Bus topology Star topology Expanding stars Ring topology Mesh topologyChapter 2: Understanding Network Protocols and Standards Understanding Protocols Understanding Standards The Seven Layers of the OSI Reference Model The Physical Layer The Data Link Layer The Network Layer The Transport Layer The Session Layer The Presentation Layer The Application Layer Following a Packet through the Layers The Ethernet Protocol Standard Ethernet
Fast Ethernet Gigabit Ethernet The TCP/IP Protocol Suite IP TCP UDP Other Protocols Worth Knowing AboutChapter 3: Understanding Network Hardware Servers Whats important in a server Components of a server computer Server form factors Network Interface Cards Network Cable Coaxial cable Twisted-pair cable Switches Repeaters Bridges Routers Network Attached Storage Network PrintersChapter 4: Understanding Network Operating Systems Network Operating System Features Network support File-sharing services Multitasking Directory services Security services Microsofts Server Operating Systems Windows 2000 Server Windows Server 2003 Windows Server 2008 Windows Server 2008 R2 Other Server Operating Systems Linux Apple Mac OS/X Server Novell NetWare Peer-to-Peer Networking with Windows Advantages of peer-to-peer networks Drawbacks of peer-to-peer networks Windows 7
Windows Vista Older Windows versionsBook IIChapter 1: Planning a Network Making a Network Plan Being Purposeful Taking Stock What you need to know Programs that gather information for you To Dedicate or Not to Dedicate: That Is the Question Types of Servers File servers Print servers Web servers Mail servers Database servers Choosing a Server Operating System Planning the Infrastructure Drawing Diagrams Sample Network Plans Building a small network: California Sport Surface, Inc. Connecting two networks: Creative Course Development, Inc. Improving network performance: DCH AccountingChapter 2: Installing Network Hardware Installing a Network Interface Card Installing Twisted-Pair Cable Cable categories Whats with the pairs? To shield or not to shield When to use plenum cable Sometimes solid, sometimes stranded Installation guidelines Getting the tools that you need Pinouts for twisted-pair cables Attaching RJ-45 connectors Crossover cables Wall jacks and patch panels Installing Coaxial Cable Attaching a BNC Connector to Coaxial Cable Installing Switches Daisy-Chaining SwitchesChapter 3: Setting Up a Network Server
The Many Ways to Install a Network Operating System Full install versus upgrade Installing over the network Automated and remote installations Gathering Your Stuff A capable server computer The server operating system Other software A working Internet connection A good book Making Informed Decisions Final Preparations Installing a Network Operating System Phase 1: Collecting Information Phase 2: Installing Windows Configuring Your ServerChapter 4: Configuring Windows Clients Configuring Network Connections Configuring Windows XP network connections Configuring Windows Vista network connections Configuring Windows 7 network connections Configuring Client Computer Identification Configuring Windows XP computer identification Configuring Windows Vista or Windows 7 computer identification Configuring Network LogonChapter 5: Macintosh Networking What You Need to Know to Hook Up a Macintosh Network Mac networking protocols Mac OS X Server What You Need to Know to Use a Macintosh Network Configuring a Mac for networking Accessing a network printer Sharing files with other users Accessing shared files What You Need to Know to Network Macintoshes with PCsChapter 6: Configuring Other Network Features Configuring Network Printers Adding a network printer Accessing a network printer using a Web interface Configuring Internet Access Configuring clients for DHCP
Using Internet Connection Sharing Mapping Network DrivesChapter 7: Verifying Your Network Installation Is the Computer Connected to the Network? Is the Network Configuration Working? Can the Computers Ping Each Other? Can You Log On? Are Network Drives Mapped Correctly? Do Network Printers Work?Chapter 8: Going Virtual Understanding Virtualization Looking at the Benefits of Virtualization Getting Started with Virtualization Creating a Virtual MachineBook IIIChapter 1: Help Wanted: Job Description for a NetworkAdministrator Knowing What Network Administrators Do Choosing the Part-Time Administrator Establishing Routine Chores Managing Network Users Patching Up Your Operating System and Software Discovering Software Tools for Network Administrators Building a Library Getting Certified CompTIA Microsoft Cisco Gurus Need Gurus, Too Helpful Bluffs and ExcusesChapter 2: Security 101 Do You Need Security? Considering Two Approaches to Security Physical Security: Locking Your Doors Securing User Accounts Obfuscating your usernames Using passwords wisely A Password Generator For Dummies Securing the Administrator account Hardening Your Network Using a firewall Disabling unnecessary services
Patching your servers Securing Your UsersChapter 3: Managing User Accounts Exploring What User Accounts Consist Of Looking at Built-In Accounts The Administrator account The Guest account Service accounts Assigning User Rights Controlling User Access with Permissions (Who Gets What) Assigning Permissions to Groups Understanding User Profiles Automating Tasks with Logon ScriptsChapter 4: Firewalls and Virus Protection Firewalls The Many Types of Firewalls Packet filtering Stateful packet inspection (SPI) Circuit-level gateway Application gateway The Built-In Windows Firewall Virus Protection What is a virus? Antivirus programs Safe computing Using Windows Action CenterChapter 5: Extending Your Network with VPN Access Understanding VPN Looking at VPN Security Understanding VPN Servers and ClientsChapter 6: Managing Network Software Understanding Software Licenses Using a License Server Options for Deploying Network Software Deploying software manually Running Setup from a network share Installing silently Creating an administrative installation image Pushing out software with group policy Keeping Software Up to DateChapter 7: Solving Network Problems When Bad Things Happen to Good Computers
Fixing Dead Computers Ways to Check a Network Connection A Bunch of Error Messages Just Flew By! Double-Checking Your Network Settings Using the Windows Networking Troubleshooter Time to Experiment Whos on First? Restarting a Client Computer Booting in Safe Mode Using System Restore Restarting Network Services Restarting a Network Server Looking at Event Logs Documenting Your Trials and TribulationsChapter 8: Network Performance Anxiety Why Administrators Hate Performance Problems What Exactly Is a Bottleneck? The Five Most Common Network Bottlenecks The hardware inside your servers The servers configuration options Servers that do too much The network infrastructure Malfunctioning components Tuning Your Network the Compulsive Way Monitoring Network Performance More Performance TipsChapter 9: Backing Up Your Data Backing Up Your Data All about Tapes and Tape Drives Backup Software Types of Backups Normal backups Copy backups Daily backups Incremental backups Differential backups Local versus Network Backups How Many Sets of Backups Should You Keep? A Word about Tape Reliability About Cleaning the Heads Backup SecurityChapter 10: Disaster Recovery and Business Continuity Planning
Assessing Different Types of Disasters Environmental disasters Deliberate disasters Disruption of services Equipment failure Other disasters Analyzing the Impact of a Disaster Developing a Business Continuity Plan Holding a Fire DrillBook IVChapter 1: Introduction to TCP/IP and the Internet What Is the Internet? A Little Internet History TCP/IP Standards and RFCs The TCP/IP Protocol Framework Network Interface layer Network layer Transport layer Application layerChapter 2: Understanding IP Addresses Understanding Binary Counting by ones Doing the logic thing Working with the binary Windows Calculator Introducing IP Addresses Networks and hosts The dotted-decimal dance Classifying IP Addresses Class A addresses Class B addresses Class C addresses Subnetting Subnets Subnet masks Network prefix notation Default subnets The great subnet roundup IP block parties Private and public addresses Network Address TranslationChapter 3: Using DHCP Understanding DHCP
Configuration information provided by DHCP DHCP servers How DHCP actually works Understanding Scopes Feeling excluded? Reservations suggested How long to lease? Working with a DHCP Server Installing and configuring a DHCP server Managing a DHCP server How to Configure a Windows DHCP Client Automatic Private IP Addressing Renewing and releasing leasesChapter 4: Using DNS Understanding DNS Names Domains and domain names Fully qualified domain names Top-Level Domains Generic domains Geographic domains The Hosts File Understanding DNS Servers and Zones Zones Primary and secondary servers Root servers Caching Understanding DNS Queries A real-life DNS example Zone Files and Resource Records SOA records NS records A records CNAME records PTR records MX records Reverse Lookup Zones Working with the Windows DNS Server How to Configure a Windows DNS ClientChapter 5: Using FTP Discovering FTP Configuring an FTP Server Installing FTP
Creating an FTP site Changing the FTP site properties Adding content to your FTP siteAccessing an FTP Site with a BrowserUsing an FTP Command Line ClientFTP Command and Subcommand Reference The FTP command ! (Escape) ? (Help) append ascii bell binary bye cd close debug delete dir disconnect get glob hash help lcd literal ls mdelete mdir mget mkdir mls mput open prompt put pwd quit quote recv remotehelp rename
rmdir send status trace type user verboseChapter 6: TCP/IP Tools and Commands Using the arp Command Using the hostname Command Using the ipconfig Command Displaying basic IP configuration Displaying detailed configuration information Renewing an IP lease Releasing an IP lease Flushing the local DNS cache Using the nbtstat Command Using the netdiag Utility Using the netstat Command Displaying connections Displaying interface statistics Using the nslookup Command Looking up an IP address Using nslookup subcommands Displaying DNS records Locating the mail server for an e-mail address Taking a ride through DNS-Land Using the pathping Command Using the ping Command Using the route Command Displaying the routing table Modifying the routing table Using the tracert CommandBook VChapter 1: Setting Up a Wireless Network Diving into Wireless Networking A Little High School Electronics Waves and frequencies Wavelength and antennas Spectrums and the FCC Eight-Oh-Two-Dot-Eleventy Something? (Or, Understanding Wireless Standards)
Home on the Range Wireless Network Adapters Wireless Access Points Infrastructure mode Multifunction WAPs Roaming Wireless bridging Ad-hoc networks Configuring a Wireless Access Point Basic configuration options DHCP configuration Configuring Windows XP for Wireless Networking Using a Wireless Network with Windows XP Connecting to a Wireless Network with Windows Vista Connecting to a Wireless Network with Windows 7Chapter 2: Securing a Wireless Network Understanding Wireless Security Threats Intruders Freeloaders Eavesdroppers Spoilers Rogue access points What About Wardrivers and Warchalkers? Wardriving Warchalking Securing Your Wireless Network Changing the password Securing the SSID Enabling WEP Using WPA Using MAC address filtering Placing your access points outside the firewallChapter 3: Hotspotting What Is a Hotspot? Whats So Great about Hotspots? Safe Hotspotting Free Hotspots Fee-Based Hotspots T-Mobile Boingo Setting Up Your Own HotspotChapter 4: Troubleshooting a Wireless Network
Checking for Obvious Problems Pinpointing the Problem Changing Channels Fiddle with the Antennas Adding Another Access Point Help! I Forgot My Routers Password!Chapter 5: Wireless Networking with Bluetooth Understanding Bluetooth Bluetooth Technical Stuff How to Add Bluetooth to Your Computer Using Bluetooth in Windows Installing a USB Bluetooth Adapter Enabling Discovery Installing a Bluetooth Mouse or KeyboardBook VIChapter 1: Managing Mobile Devices The Many Types of Mobile Devices Considering Security for Mobile DevicesChapter 2: Managing BlackBerry Devices Understanding BlackBerry Adding a BES User Locking and Erasing a HandheldChapter 3: Managing iPhone Devices Understanding the iPhone Integrating iPhone with Exchange Enabling Exchange Mobile Services Enabling ActiveSync for a users mailbox Configuring the iPhone for Exchange e-mailChapter 4: Managing Android Devices Understanding Android Phones Looking at the Android Operating System Perusing Androids Core Applications Integrating Android with ExchangeChapter 5: Managing Netbooks Understanding Netbook Computers Connecting with a Netbook Tips for Using a Netbook EffectivelyBook VIIChapter 1: Installing and Configuring Windows Server 2008 R2 Planning a Windows Server Installation Checking system requirements Reading the release notes
Deciding whether to upgrade or install Considering your licensing options Thinking about multiboot Choosing a file system Planning your partitions Deciding your TCP/IP configuration Choosing workgroups or domains Before You Install . . . Backing up Checking the event logs Uncompressing data Disconnecting UPS devices Running Setup Adding Server Roles and FeaturesChapter 2: Managing Windows Server 2008 Using the Administrator Account Using Remote Desktop Connection Enabling remote access Connecting remotely Using Microsoft Management Console Working with MMC An overview of the MMC consoles Customizing MMC Adding snap-ins Adding taskpadsChapter 3: Dealing with Active Directory What Directories Do Remembering the Good-Ol Days of NT Domains PDCs and BDCs Trusts NetBIOS names Active Directory to the Rescue Understanding How Active Directory Is Structured Objects Domains Organizational units Trees Forests Creating a Domain Creating an Organizational UnitChapter 4: Managing Windows User Accounts Understanding Windows User Accounts
Local accounts versus domain accounts User account properties Creating a New User Setting User Properties Changing the users contact information Setting account options Specifying logon hours Restricting access to certain computers Setting the users profile information Resetting User Passwords Disabling and Enabling User Accounts Deleting a User Working with Groups Group types Group scope Default groups Creating a group Adding a member to a group User Profiles Types of user profiles Creating a roaming profile Creating a Logon ScriptChapter 5: Managing a File Server Understanding Permissions Understanding Shares Configuring the File Server Role Managing Your File Server Using the Provision a Shared Folder Wizard Sharing a folder without the wizard Granting permissionsChapter 6: Using Group Policy Understanding Group Policy Enabling Group Policy Management on Windows Server 2008 Creating Group Policy Objects Filtering Group Policy ObjectsChapter 7: Troubleshooting Working with the Event Viewer Using the Event Viewer Setting event log policies Monitoring Performance Using the Reliability and Performance Monitor Creating performance logs
Using the Computer Management Console Working with ServicesChapter 8: Windows Commands Using a Command Window Opening and closing a command window Editing commands Using the Control menu Special Command Tricks Wildcards Chaining commands Redirection and piping Environment variables Batch files The EventCreate Command Net Commands The Net Accounts command The Net Computer command The Net Config command The Net Continue command The Net File command The Net Group command The Net Help command The Net Helpmsg command The Net Localgroup command The Net Name command The Net Pause command The Net Print command The Net Send command The Net Session command The Net Share command The Net Start command The Net Statistics command The Net Stop command The Net Time command The Net Use command The Net User command The Net View command The RunAs CommandBook VIIIChapter 1: Using Internet Information System (IIS) Installing IIS Understanding the Default Web Site
Creating Web SitesChapter 2: Managing Exchange Server 2010 Creating a Mailbox Managing Mailboxes Enabling Mailbox Features Creating a Forwarder Setting Mailbox Storage Limits Configuring Outlook for Exchange Viewing Another MailboxChapter 3: Using SQL Server 2008 What Is a Database? What Is a Relational Database? What Is SQL? SQL dialects SQL statements Using the select statement Installing SQL Server 2008 Using the SQL Server 2008 Management Studio Creating a New Database Creating Tables Editing Tables Working with Queries Working with ScriptsChapter 4: Using SharePoint What Is SharePoint? Connecting to a SharePoint Site Adding Users Adding and Removing Announcements Creating New Pages Editing the Quick Launch Menu Working with Document LibrariesBook IXChapter 1: Installing a Linux Server Planning a Linux Server Installation Checking system requirements Choosing a distribution Thinking about multiboot Planning your partitions Deciding on your TCP/IP configuration Installing Fedora 7 Using the Setup AgentChapter 2: Getting Used to Linux
Linux: It Isnt Windows X Window Virtual consoles Understanding the file system On Again, Off Again Logging on Logging off Shutting down Using GNOME Getting to a Command Shell Managing User AccountsChapter 3: Basic Linux Network Configuration Using the Network Configuration Program Restarting Your Network Working with Network Configuration Files The Network file The ifcfg files The Hosts file The resolv.conf file The nsswitch.conf file The xinetd.conf file Displaying Your Network Configuration with the ifconfig CommandChapter 4: Running DHCP and DNS Running a DHCP Server Installing DHCP Configuring DHCP Starting DHCP Running a DNS Server Installing BIND Looking at BIND configuration files Restarting BINDChapter 5: Doing the Samba Dance Understanding Samba Installing Samba Starting and Stopping Samba Using the Samba Server Configuration Tool Configuring server settings Configuring Samba users Creating a share Editing the smb.conf File Using the Samba Client
Chapter 6: Running Apache Installing Apache Starting and Stopping Apache Confirming that Apache Is Running Using the HTTP Configuration Tool Restricting Access to an Apache Server Configuring Virtual Hosts Configuring the default host Creating a virtual host Setting the Apache User Account Manually Editing Apaches Configuration Files Creating Web PagesChapter 7: Running Sendmail Understanding E-Mail Installing Sendmail Modifying sendmail.mc Enabling connections Enabling masquerading Setting up aliases Using SpamAssassin Installing SpamAssassin Customizing SpamAssassin Blacklisting and whitelisting e-mail addresses Using the Mail Console Client Using EvolutionChapter 8: Running FTP Installing vsftpd Starting the vsftpd Service Configuring FTPChapter 9: Linux Commands Command Shell Basics Getting to a shell Editing commands Wildcards Redirection and piping Environment variables Shell scripts Directory and File Handling Commands The pwd command The cd command The mkdir command The rmdir command
The ls command The cp command The rm command The mv command The touch command The cat command Commands for Working with Packages and Services The service command The rpm command Commands for Administering Users The useradd command The usermod command The userdel command The chage command The passwd command The newusers command The groupadd command The groupdel command The gpasswd command Commands for Managing Ownership and Permissions The chown command The chgrp command The chmod command Networking Commands The hostname command The ifconfig command The netstat command The ping command The route command The traceroute commandAppendix A: Directory of Useful Web Sites Certification Hardware Home and Small Business Networking Linux Magazines Microsoft Network Standards Organizations Reference Search TCP/IP and the Internet Wireless Networking
Smartphones Appendix B: Glossary Networking Basics Chapter 1: Understanding NetworksIn This Chapter Introducing computer networks Finding out all about clients, servers, and peers Understanding the various types of networks Figuring out the disadvantages of networkingThe first computer network was invented when ancient mathematicians connected their abacuses (or isit abaci?) together with kite string so they could instantly share their abacus answers with each other.Over the years, computer networks became more and more sophisticated. Now, instead of string,networks use electrical cables, fiber-optic cables, or wireless radio signals to connect computers to eachother. The purpose, however, has remained the same: sharing information and getting work done faster.This chapter describes the basics of what computer networking is and how it works.What Is a Network?A network is nothing more than two or more computers connected to each other so that they canexchange information, such as e-mail messages or documents, or share resources, such as disk storage orprinters. In most cases, this connection is made via electrical cables that carry the information in the formof electrical signals. But in some cases, other types of connections are used. For example, fiber-opticcables let computers communicate at extremely high speeds by using impulses of light. Wireless networkslet computers communicate by using radio signals, so the computers arent restricted by physical cables.In addition to the hardware that comprises the network, a network also requires special software to enablecommunications. In the early days of networking, you had to add this software to each computer on thenetwork. Nowadays, network support is built in to all major operating systems, including all currentversions of Windows, Macintosh operating systems, and Linux.Network building blocks
All networks, large or small, require specialized network hardware to make them work. For smallnetworks, the hardware may consist of nothing more than a collection of computers that are equippedwith network ports, a cable for each computer, and a network switch that all the computers plug in to viathe cable. Larger networks probably have additional components, such as routers or repeaters.Small or large, all networks are built from the following basic building blocks:♦ Client computers: The computers that end users use to access the resources of the network. Clientcomputers are typically computers located on users desks. They usually run a desktop version ofWindows such as Windows 7, Vista, or XP. In addition, the client computers usually run some type ofapplication software such as Microsoft Office. Client computers are sometimes referred toas workstations.♦ Server computers: Computers that provide shared resources, such as disk storage and printers, aswell as network services, such as e-mail and Internet access. Server computers typically run a specializednetwork operating system such as Windows Server 2008 or 2003, NetWare, or Linux, along with specialsoftware to provide network services. For example, a server may run Microsoft Exchange to provide e-mail services for the network, or it may run Apache Web Server so that the computer can serve Webpages.♦ Network interface: An interface — sometimes called a network port — thats installed in a computerto enable the computer to communicate over a network. Almost all network interfaces implement anetworking standard called Ethernet.A network interface is sometimes called a NIC, which stands for network interface card,because in theearly days of networking you actually had to install a separate circuit card in the computer to provide anetwork interface. Nowadays, nearly all computers come with network interfaces built in as an integralpart of the computers motherboard. Although separate network cards are rarely required these days, theterm NIC is still frequently used to refer to the network interface. Its still common to install separate network interface cards to provide more than one networkinterface on a single computer, or to replace a built-in network interface that has malfunctioned withouthaving to replace the entire motherboard.♦ Cable: Computers in a network are usually physically connected to each other using cable. Althoughseveral types of cable have been popular over the years, most networks today use a type of cablecalled twisted-pair, also known by its official designation10BaseT.Twisted-pair cable is also sometimes referred to as Cat-5 or Cat-6 cable. These terms refer to thestandards that determine the maximum speed with which the cable can carry data, Cat-6 being rated formore speed than Cat-5.Twisted-pair cable can also be referred to simply as copper, to distinguish it from fiber-optic cable whichis used for the highest-speed network connections. Fiber-optic cable uses strands of glass to transmit lightsignals at very high speeds.In many cases, the cables run through the walls and converge on a central room called awiring closet. Butfor smaller networks, the cables are often just strung along the floor, hidden behind desks and otherfurniture whenever possible.♦ Switches: Network cable usually doesnt connect computers directly to each other. Instead, eachcomputer is connected by cable to a device known as a switch. The switch, in turn, connects to the rest ofthe network. Each switch contains a certain number of ports,typically 8 or 16. Thus, you can use an eight-port switch to connect up to eight computers. Switches can be connected to each other to build largernetworks. For more information about switches, see the "Network Topology" section later in this chapter.(Older networks may use a more primitive type of device called a hub instead of a switch. A hub providesthe same function as a switch, but it isnt as efficient. The term hub is sometimes used tomeanswitch, even though hubs and switches are not technically the same thing.)♦ Wireless networks: In many networks, cables and switches are making way for wireless networkconnections, which enable computers to communicate via radio signals. In a wireless network, radiotransmitters and receivers take the place of cables. The main advantage of wireless networking is itsflexibility. With a wireless network, you dont have to run cables through walls or ceilings, and your clientcomputers can be located anywhere within range of the network broadcast. The main disadvantage ofwireless networking is that its inherently less secure than a cabled network.
♦ Network software: Although network hardware is essential, what really makes a network work issoftware. A whole bunch of software has to be set up just right in order to get a network working. Servercomputers typically use a special network operating system(also known as a NOS) in order to functionefficiently, and client computers need to have their network settings configured properly in order to accessthe network.One of the most important networking choices to make is which network operating system youll use onthe networks servers. Thats because much of the task of building a new network and managing anexisting one is setting up and maintaining the network operating system on the servers.Why bother?If the truth be told, computer networks are a pain to set up. So, why bother? Because the benefits ofhaving a network make the difficulty of setting one up worthwhile. You dont have to be a Ph.D. tounderstand the benefits of networking. In fact, you learned everything you need to know about thebenefits of networking in kindergarten. Networks are all about sharing. Specifically, networks are aboutsharing three things: information, resources, and applications.♦ Sharing information: Networks allow users to share information in several different ways. The mostcommon way of sharing information is to share individual files. For example, two or more people canwork together on a single spreadsheet file or word-processing document. In most networks, a large harddrive on a central server computer is set up as a common storage area where users can store files to beshared with other users.In addition to sharing files, networks allow users to communicate with each other in various ways. Forexample, messaging applications let network users exchange messages with each other using an e-mailapplication such as Microsoft Outlook. Users can also hold online meetings over the network. In fact, withinexpensive video cameras and the right software, users can hold videoconferences over the network.♦ Sharing resources: Certain computer resources, such as printers or hard drives, can be set up so thatnetwork users can share them. Sharing these resources can result in significant cost savings. For example,its cheaper to buy a single high-speed printer with advanced features such as collating, stapling, andduplex printing that can be shared by an entire workgroup than it is to buy separate printers for each userin the group.Hard drives can also be shared resources. In fact, providing users with access to a shared hard drive is themost common method of sharing files on a network. A computer whose main purpose in life is to hostshared hard drives is called a file server.In actual practice, entire hard drives arent usually shared. Instead, individual folders on a networkedhard drive are shared. This way, the network administrator can allow different network users to haveaccess to different shared folders. For example, a company may set up shared folders for its salesdepartment and accounting department. Then, sales personnel can access the sales departments folder,and accounting personnel can access the accounting departments folder.You can share other resources on a network. For example, a network can be used to share an Internetconnection. In the early days of the Internet, it was common for each user who required access to theInternet to have his or her own modem connection. Nowadays, its more common for the network toprovide a shared, high-speed Internet connection that everyone on the network can access.♦ Sharing applications: One of the most common reasons for networking in many businesses is so thatseveral users can work together on a single business application. For example, an accounting departmentmay have accounting software that can be used from several computers at the same time. Or a sales-processing department may have an order-entry application that runs on several computers to handle alarge volume of orders.Of Clients and Servers The network computer that contains the hard drives, printers, and other resources that areshared with other network computers is called a server. This term comes up repeatedly, so you have toremember it. Write it on the back of your left hand.Any computer thats not a server is called a client. You have to remember this term, too. Write it on theback of your right hand.Only two kinds of computers are on a network: servers and clients. Look at your left hand and then look atyour right hand. Dont wash your hands until you have these terms memorized.
The distinction between servers and clients in a network would be somewhat fun to study in a sociologyclass because its similar to the distinction between the haves and the have-nots in society:♦ Usually, the most powerful and expensive computers in a network are the servers. This fact makes sensebecause every user on the network shares the servers resources.♦ The cheaper and less powerful computers in a network are the clients. Clients are the computers used byindividual users for everyday work. Because clients resources dont have to be shared, they dont have tobe as fancy.♦ Most networks have more clients than servers. For example, a network with ten clients can probably getby with one server.♦ In some networks, a clear line of segregation exists between servers and clients. In other words, acomputer is either a server or a client, and not both. A server cant become a client, nor can a clientbecome a server.♦ Other networks are more progressive, allowing any computer in the network to be a server and allowingany computer to be both server and client at the same time. The network illustrated in Figure 1-1, later inthis chapter, is this type of network.Dedicated Servers and PeersIn some networks, a server computer is a server computer and nothing else. This server computer isdedicated solely to the task of providing shared resources, such as hard drives and printers, to be accessedby the network client computers. Such a server is referred to as a dedicated server because it can performno other tasks besides network services. A network that relies on dedicated servers is sometimes calleda client/server network.Other networks take an alternative approach, enabling any computer on the network to function as both aclient and a server. Thus, any computer can share its printers and hard drives with other computers onthe network. And while a computer is working as a server, you can still use that same computer for otherfunctions such as word processing. This type of network is called a peer-to-peer network because all thecomputers are thought of as peers, or equals.While youre walking the dog tomorrow morning, ponder these points concerning the difference betweendedicated server networks and peer-to-peer networks:♦ Peer-to-peer networking has been built in to all versions of Windows since Windows 95. Thus, you donthave to buy any additional software to turn your computer into a server. All you have to do is enable theWindows server features.♦ The network server features that are built in to desktop versions of Windows (including Windows 7,Vista, and XP) arent very efficient because these versions of Windows were not designed primarily to benetwork servers. If youre going to dedicate a computer to the task of being a full-time server, you shoulduse a full-fledged network operating system, such as Windows Server 2008, instead.Networks Big and SmallNetworks come in all sizes and shapes. In fact, its common to categorize networks based on thegeographical size they cover, as described in the following list:♦ Local area networks: A local area network, or LAN, is a network in which computers are relativelyclose together, such as within the same office or building.Note that the term LAN doesnt imply that the network is small. A LAN can, in fact, contain hundreds oreven thousands of computers. What makes a network a LAN is that all those computers are located withinclose proximity to each other. Usually a LAN is contained within a single building, but a LAN can extendto several buildings on a campus — provided the buildings are close to each other (typically within 300feet of each other, though greater distances are possible with special equipment).♦ Wide area networks: A wide area network, or WAN, is a network that spans a large geographicterritory, such as an entire city or region, or even an entire country. WANs are typically used to connecttwo or more LANs that are relatively far apart. For example, a WAN may connect an office in SanFrancisco with an office in New York.Again, its the geographic distance, not the number of computers involved, that makes a network a WAN.If the office in San Francisco and the office in New York both have only one computer, the WAN will havea total of two computers but will span more than 3,000 miles.♦ Metropolitan area networks: A metropolitan area network, or MAN, is a network thats smallerthan a typical WAN but larger than a LAN. Typically, a MAN connects two or more LANs that are within
the same city but are far enough apart that the networks cant be connected using a simple cable orwireless connection.Network TopologyThe term network topology refers to the shape of how the computers and other network components areconnected to each other. There are several different types of network topologies, each with advantages anddisadvantages.In the following discussion of network topologies, I use two important terms:♦ Node: A node is a device thats connected to the network. For your purposes here, a node is the same asa computer. Network topology deals with how the nodes of a network are connected to each other.♦ Packet: A packet is a message thats sent over the network from one node to another node. The packetincludes the address of the node that sent the packet, the address of the node the packet is being sent to,and data.Bus topologyThe first type of network topology is called a bus, in which nodes are strung together in a line, as shown inFigure 1-1. The key to understanding how a bus topology works is to think of the entire network as a singlecable, with each node "tapping" into the cable so it can listen in on the packets being sent over that cable.If youre old enough to remember party lines, you get the idea.Figure 1-1: Bus topology.In a bus topology, every node on the network can see every packet thats sent on the cable. Each nodelooks at each packet to determine whether the packet is intended for it. If so, the node claims the packet.If not, the node ignores the packet. This way, each computer can respond to data sent to it and ignore datasent to other computers on the network.If the cable in a bus network breaks, the entire network is effectively disabled. Obviously the nodes onopposite sides of the break cant continue to communicate with each other because data cant span the gapcreated by the break. But even those nodes that are on the same side of the break will be unable tocommunicate with each other, because the open end of the cable left by the break disrupts the propertransmission of electrical signals.In the early days of Ethernet networking, bus topology was commonplace. Although bus topology hasgiven way to star topology (see the next section) for most networks today, many networks today still haveelements that rely on bus topology.Star topologyIn a star topology, each network node is connected to a central device called a hub or aswitch, as shown inFigure 1-2. Star topologies are commonly used with LANs.If a cable in a star network breaks, only the node connected to that cable is isolated from the network. Theother nodes can continue to operate without interruption — unless, of course, the node thats isolatedbecause of the break happens to be the file server. You should be aware of the somewhat technical distinction between a hub and a switch. Simplyput, a hub doesnt know anything about the computers that are connected to each of its ports. So when acomputer connected to the hub sends a packet to a computer thats connected to another port, the hub
sends a duplicate copy of the packet to all its ports. In contrast, a switch knows which computer isconnected to each of its ports. As a result, when a switch receives a packet intended for a particularcomputer, it sends the packet only to the port that the recipient is connected to.Figure 1-2: Star topology.Strictly speaking, only networks that use switches have a true star topology. If the network uses a hub, thenetwork topology has the physical appearance of a star, but is actually a bus. Thats because when a hub isused, each computer on the network sees all the packets sent over the network, just like in a bus topology.In a true star topology, as when a switch is used, each computer sees only those packets that were sentspecifically to it, as well as packets that were specifically sent to all computers on the network (those typesof packets are called broadcast packets).Expanding starsPhysicists say that the universe is expanding, and network administrators know theyre right. A simplebus or star topology is suitable only for small networks, with a dozen or so computers. But small networksinevitably become large networks as more computers are added. For larger networks, its common tocreate more complicated topologies that combine stars and buses.For example, a bus can be used to connect several stars. In this case, two or more hubs or switches areconnected to each other using a bus. Each of these hubs or switches is then the center of a star thatconnects two or more computers to the network. This type of arrangement is commonly used in buildingsthat have two or more distinct workgroups. The bus that connects the switches is sometimes calleda backbone.Another way to expand a star topology is to use a technique called daisy-chaining. When you use daisy-chaining, a switch is connected to another switch as if it were one of the nodes on the star. Then, thissecond switch serves as the center of a second star.Ring topology
A third type of network topology is called a ring, shown in Figure 1-3. In a ring topology, packets are sentaround the circle from computer to computer. Each computer looks at each packet to decide whether thepacket was intended for it. If not, the packet is passed on to the next computer in the ring.Figure 1-3: Ring topology.Years ago, ring topologies were common in LANs, as two popular networking technologies used rings:ARCNET and Token Ring. ARCNET is still used for certain applications such as factory automation, but israrely used in business networks. Token Ring is still a popular network technology for IBM midrangecomputers. Although plenty of Token Ring networks are still in existence, not many new networks useToken Ring any more.Ring topology was also used by FDDI, one of the first types of fiber-optic network connections. FDDI hasgiven way to more efficient fiber-optic techniques, however. So ring networks have all but vanished frombusiness networks.Mesh topologyA fourth type of network topology, known as mesh, has multiple connections between each of the nodeson the network, as shown in Figure 1-4. The advantage of a mesh topology is that if one cable breaks, thenetwork can use an alternative route to deliver its packets.Figure 1-4: Mesh topology.
Mesh networks arent very practical in a LAN setting. For example, to network eight computers in a meshtopology, each computer would have to have seven network interface cards, and 28 cables would berequired to connect each computer to the seven other computers in the network. Obviously, this schemeisnt very scalable.However, mesh networks are common for metropolitan or wide area networks. These networks usedevices called routers to route packets from network to network. For reliability and performance reasons,routers are usually arranged in a way that provides multiple paths between any two nodes on the networkin a meshlike arrangement. Chapter 2: Understanding Network Protocols and StandardsIn This Chapter Deciphering the layers of the OSI reference model Understanding an Ethernet Getting the inside scoop on TCP/IP and IPX/SPX Finding out about other important protocolsProtocols and standards are what make networks work together. Protocols make it possible for the variouscomponents of a network to communicate with each other. Standards also make it possible for networkcomponents manufactured by different companies to work together. This chapter introduces you to theprotocols and standards that youre most likely to encounter when building and maintaining a network.Understanding ProtocolsA protocol is a set of rules that enables effective communications to occur. You encounter protocols everyday. For example, when you pay for groceries with a debit card, the clerk first tells you how much thegroceries cost. You then swipe your debit card in the card reader, punch in your security code, indicatewhether you want cash back, enter the amount of the cash back if you so indicated, then verify the totalamount. You then cross your fingers behind your back and say a quiet prayer while the machineauthorizes the purchase. Assuming the amount is authorized, the machine prints out your receipt.Heres another example of an everyday protocol: making a phone call. You probably take most of thedetails of the phone-calling protocol for granted, but its pretty complicated if you think about it:♦ When you pick up a phone, you must listen for a dial tone before dialing the number (unless youreusing a cell phone). If you dont hear a dial tone, you know that either (1) someone else in your family istalking on the phone or (2) something is wrong with your phone.♦ When you hear the dial tone, you initiate the call by dialing the number of the party you want to reach. Ifthe person you want to call is in the same area code as you, most of the time you simply dial that personsseven-digit phone number. If the person is in a different area code, you dial a one, the three-digit areacode, and the persons seven-digit phone number.♦ If you hear a series of long ringing tones, you wait until the other person answers the phone. If thephone rings a certain number of times with no answer, you hang up and try again later. If you hear a voicesay, "Hello," you begin a conversation with the other party. If the person on the other end of the phonehas never heard of you, you say, "Sorry, wrong number," hang up, and try again.
♦ If you hear a voice that rambles on about how theyre not home but they want to return your call, youwait for a beep and leave a message.♦ If you hear a series of short tones, you know the other person is talking to someone else on the phone. Soyou hang up and try again later.♦ If you hear a sequence of three tones that increase in pitch, followed by a recorded voice that says "Weresorry . . ." you know that the number you dialed is invalid. Either you dialed the number incorrectly, or thenumber has been disconnected.I can go on and on, but I think you probably get the point. Exchanges such as using debit cards or makingphone calls follow the same rules every time they happen.Computer networks depend upon many different types of protocols in order to work. These protocols arevery rigidly defined, and for good reason. Network cards must know how to talk to other network cards inorder to exchange information, operating systems must know how to talk to network cards in order tosend and receive data on the network, and application programs must know how to talk to operatingsystems in order to know how to retrieve a file from a network server.Protocols come in many different types. At the lowest level, protocols define exactly what type of electricalsignal represents a one and what type of signal represents a zero. At the highest level, protocols allow acomputer user in the United States to send an e-mail to another computer user in New Zealand. And inbetween are many other levels of protocols. You find out more about these levels of protocols (which areoften called layers) in the section, "The Seven Layers of the OSI Reference Model," later in this chapter. Various protocols tend to be used together in matched sets called protocol suites. The two mostpopular protocol suites for networking are TCP/IP andEthernet. TCP/IP was originally developed forUnix networks and is the protocol of the Internet and most local-area networks. Ethernet is a low-levelprotocol that spells out the electrical characteristics of the network hardware used by most local-areanetworks. A third important protocol is IPX/SPX, which is an alternative to TCP/IP that was originallydeveloped for NetWare networks. In the early days of networking, IPX/SPX was widely used in local areanetworks, but TCP/IP is now the preferred protocol.Understanding StandardsA standard is an agreed-upon definition of a protocol. In the early days of computer networking, eachcomputer manufacturer developed its own networking protocols. As a result, you werent able to easilymix equipment from different manufacturers on a single network.Then along came standards to save the day. Standards are industry-wide protocol definitions that are nottied to a particular manufacturer. With standard protocols, you can mix and match equipment fromdifferent vendors. As long as the equipment implements the standard protocols, it should be able tocoexist on the same network.Many organizations are involved in setting standards for networking. The five most importantorganizations are♦ American National Standards Institute (ANSI): The official standards organization in the UnitedStates. ANSI is pronounced AN-see.♦ Institute of Electrical and Electronics Engineers (IEEE): An international organization thatpublishes several key networking standards — in particular, the official standard for the Ethernetnetworking system (known officially as IEEE 802.3). IEEE is pronounced eye-triple-E.♦ International Organization for Standardization (ISO): A federation of more than 100 standardsorganizations from throughout the world. If I had studied French in high school, Id probably understandwhy the acronym for International Organization for Standardization is ISO, and not IOS.♦ Internet Engineering Task Force (IETF): The organization responsible for the protocols that drivethe Internet.♦ World Wide Web Consortium (W3C): An international organization that handles the developmentof standards for the World Wide Web.Table 2-1 lists the Web sites for each of these standards organizations.
The Seven Layers of the OSI Reference ModelOSI sounds like the name of a top-secret government agency you hear about only in Tom Clancy novels.What it really stands for in the networking world is Open Systems Interconnection, as in the OpenSystems Interconnection Reference Model, affectionately known as the OSI model.The OSI model breaks the various aspects of a computer network into seven distinct layers. These layersare kind of like the layers of an onion: Each successive layer envelops the layer beneath it, hiding itsdetails from the levels above. The OSI model is also like an onion in that if you start to peel it apart to havea look inside, youre bound to shed a few tears.The OSI model is not a networking standard in the same sense that Ethernet and TCP/IP are networkingstandards. Rather, the OSI model is a framework into which the various networking standards can fit. TheOSI model specifies what aspects of a networks operation can be addressed by various networkstandards. So, in a sense, the OSI model is sort of a standard of standards.Table 2-2 summarizes the seven layers of the OSI model.
The first three layers are sometimes called the lower layers. They deal with the mechanics of howinformation is sent from one computer to another over a network. Layers 4 through 7 are sometimescalled the upper layers. They deal with how application software can relate to the network throughapplication programming interfaces.The following sections describe each of these layers in greater detail. The seven layers of the OSI model are a somewhat idealized view of how networking protocolsshould work. In the real world, actual networking protocols dont follow the OSI model to the letter. Thereal world is always messier than wed like. Still, the OSI model provides a convenient — if not completelyaccurate — conceptual picture of how networking works.The Physical LayerThe bottom layer of the OSI model is the Physical layer. It addresses the physical characteristics of thenetwork, such as the types of cables used to connect devices, the types of connectors used, how long thecables can be, and so on. For example, the Ethernet standard for 10BaseT cable specifies the electricalcharacteristics of the twisted-pair cables, the size and shape of the connectors, the maximum length of thecables, and so on. The star, bus, ring, and mesh network topologies described in Book I, Chapter 1 apply tothe Physical layer.Another aspect of the Physical layer is the electrical characteristics of the signals used to transmit dataover the cables from one network node to another. The Physical layer doesnt define any meaning to thosesignals other than the basic binary values of zero and one. The higher levels of the OSI model must assignmeanings to the bits that are transmitted at the Physical layer.One type of Physical layer device commonly used in networks is a repeater. A repeater is used toregenerate the signal whenever you need to exceed the cable length allowed by the Physical layerstandard. 10BaseT hubs are also Physical layer devices. Technically, theyre known as multiportrepeaters because the purpose of a hub is to regenerate every packet received on any port on all of thehubs other ports. Repeaters and hubs dont examine the contents of the packets that they regenerate. Ifthey did, they would be working at the Data Link layer, and not at the Physical layer.The network adapter (also called a network interface card or NIC) thats installed in each computer onthe network is a Physical layer device. You can display information about the network adapter (oradapters) installed in a Windows computer by displaying the adapters Properties dialog box, as shown inFigure 2-1. To access this dialog box in Windows 7 or Vista, open the Control Panel, choose Network andInternet, choose View Network Status and Tasks, and choose Change Adapter Settings. Then, right-clickthe Local Area Connection icon and choose Properties from the menu that appears.Figure 2-1: The Properties dialog box for a network adapter.
The Data Link LayerThe Data Link layer is the lowest layer at which meaning is assigned to the bits that are transmitted overthe network. Data link protocols address things such as the size of each packet of data to be sent, a means
of addressing each packet so that its delivered to the intended recipient, and a way to ensure that two ormore nodes dont try to transmit data on the network at the same time.The Data Link layer also provides basic error detection and correction to ensure that the data sent is thesame as the data received. If an uncorrectable error occurs, the data link standard must specify how thenode is to be informed of the error so that it can retransmit the data.At the Data Link layer, each device on the network has an address known as the Media Access Controladdress, or MAC address. This address is actually hard-wired into every network device by themanufacturer. MAC addresses are unique; no two network devices made by any manufacturer anywherein the world can have the same MAC address.You can see the MAC address for a computers network adapter by opening a command window andrunning the ipconfig /all command, as shown in Figure 2-2. In this example, the MAC address of thenetwork card is A4-BA-DB-01-99-E8. (The ipconfigcommand refers to the MAC address asthe physical address.)Figure 2-2: Using the ipconfig /all command to display the MAC address of a network adapter. One of the most import functions of the Data Link layer is to provide a way for packets to be sentsafely over the physical media without interference from other nodes attempting to send packets at thesame time. The two most popular ways to do this are CSMA/CD and token passing. Ethernet networks useCSMA/CD, and Token Ring networks use token passing.Two types of Data Link layer devices are commonly used on networks: bridges and switches. A bridge isan intelligent repeater that is aware of the MAC addresses of the nodes on either side of the bridge andcan forward packets accordingly. A switch is an intelligent hub that examines the MAC address of arrivingpackets in order to determine which port to forward the packet to.
An important function of the Data Link layer is to make sure that two computers dont try tosend packets over the network at the same time. If they do, the signals will collide with each other, and thetransmission will be garbled. Ethernet accomplishes this feat by using a techniquecalled CSMA/CD, which stands for carrier sense multiple access with collision detection. This phrase is amouthful, but if you take it apart piece by piece, youll get an idea of how it works.Carrier sense means that whenever a device wants to send a packet over the network media, it first listensto the network media to see whether anyone else is already sending a packet. If it doesnt hear any othersignals on the media, the computer assumes that the network is free, so it sends the packet.Multiple access means that nothing prevents two or more devices from trying to send a message at thesame time. Sure, each device listens before sending. However, suppose that two devices listen, hearnothing, and then proceed to send their packets at the same time? Picture what happens when you andsomeone else arrive at a four-way stop sign at the same time. You wave the other driver on, he or shewaves you on, you wave, he or she waves, you both wave, and then you both go at the same time.Collision detection means that after a device sends a packet, it listens carefully to see whether the packetcrashes into another packet. This is kind of like listening for the screeching of brakes at the four-way stop.If the device hears the screeching of brakes, it waits a random period of time and then tries to send thepacket again. Because the delay is random, two packets that collide are sent again after different delayperiods, so a second collision is unlikely.CSMA/CD works pretty well for smaller networks. After a network hits about 30 computers, however,packets start to collide like crazy, and the network slows to a crawl. When that happens, the networkshould be divided into two or more separate sections that are sometimes called collision domains.The Network LayerThe Network layer handles the task of routing network messages from one computer to another. The twomost popular layer 3 protocols are IP (which is usually paired with TCP) and IPX (normally paired withSPX for use with Novell and Windows networks).Network layer protocols provide two important functions: logical addressing and routing. The followingsections describe these functions.Logical addressingAs you know, every network device has a physical address called a MAC address, which is assigned to thedevice at the factory. When you buy a network interface card to install into a computer, the MAC addressof that card is fixed and cant be changed. But what if you want to use some other addressing scheme torefer to the computers and other devices on your network? This is where the concept of logicaladdressing comes in; a logical address lets you access a network device by using an address that youassign.Logical addresses are created and used by Network layer protocols such as IP or IPX. The Network layerprotocol translates logical addresses to MAC addresses. For example, if you use IP as the Network layerprotocol, devices on the network are assigned IP addresses such as 188.8.131.52. Because the IP protocolmust use a Data Link layer protocol to actually send packets to devices, IP must know how to translate theIP address of a device to the devices MAC address. You can use the ipconfig command shown earlier in Figure 2-2 to see the IP address of yourcomputer. The IP address shown in the figure is 192.168.1.100. Another way to display this information isto use the System Information command, found on the Start menu under Start⇒AllPrograms⇒Accessories⇒System Tools⇒System Information. The IP address is highlighted in Figure 2-3.Notice that the System Information program displays a lot of other useful information about the networkbesides the IP address. For example, you can also see the MAC address, what protocols are being used,and other information.Figure 2-3: Displaying network information using the System Information program.
Although the exact format of logical addresses varies depending on the protocol being used, mostprotocols divide the logical address into two parts: a network address and a device address. The networkaddress identifies which network the device resides on, and the device address then identifies the deviceon that network. For example, in a typical IP address, such as 192.168.1.102, the network address is192.168.1, and the device address (called a host address in IP) is 102.Similarly, IPX addresses consist of two parts: a network address and a node address. In an IPX address,the node address is the same as the MAC address. As a result, IPX doesnt have to translate between layer3 and layer 2 addresses.RoutingRouting comes into play when a computer on one network needs to send a packet to a computer onanother network. In this case, a device called a router is used to forward the packet to the destinationnetwork. In some cases, a packet may actually have to travel through several intermediate networks inorder to reach its final destination network. You can find out more about routers in Book I, Chapter 3.An important feature of routers is that you can use them to connect networks that use different layer 2protocols. For example, a router can be used to send a packet from an Ethernet to a Token Ring network.As long as both networks support the same layer 3 protocol, it doesnt matter whether their layer 1 andlayer 2 protocols are different. A protocol is considered routable if it uses addresses that include a network part and a host part.Any protocol that uses physical addresses isnt routable because physical addresses dont indicate to whichnetwork a device belongs.The Transport Layer
The Transport layer is the layer where youll find two of the most well-known networking protocols: TCP(normally paired with IP) and SPX (normally paired with IPX). As its name implies, the Transport layer isconcerned with the transportation of information from one computer to another.The main purpose of the Transport layer is to ensure that packets are transported reliably and withouterrors. The Transport layer does this task by establishing connections between network devices,acknowledging the receipt of packets, and resending packets that arent received or are corrupted whenthey arrive.In many cases, the Transport layer protocol divides large messages into smaller packets that can be sentover the network efficiently. The Transport layer protocol reassembles the message on the receiving end,making sure that all the packets that comprise a single transmission are received so that no data is lost.For some applications, speed and efficiency are more important than reliability. In such cases,a connectionless protocol can be used. A connectionless protocol doesnt go to the trouble of establishing aconnection before sending a packet. Instead, it simply sends the packet. TCP is a connection-orientedTransport layer protocol. The connectionless protocol that works alongside TCP is called UDP.In Windows XP or Vista, you can view information about the status of TCP and UDP connections byrunning the Netstat command from a command window, as Figure 2-4 shows. In the figure, you can seethat several TCP connections are established.Figure 2-4: Using the Netstat command.In fact, you can use the command Netstat /N to see the numeric network addresses instead of thenames. With the /N switch, the output in Figure 2-4 would look like this:Active Connections Proto Local Address Foreign Address State TCP 127.0.0.1:2869 127.0.0.1:54170 ESTABLISHED TCP 127.0.0.1:5357 127.0.0.1:54172 TIME_WAIT TCP 127.0.0.1:27015 127.0.0.1:49301 ESTABLISHED TCP 127.0.0.1:49301 127.0.0.1:27015 ESTABLISHED TCP 127.0.0.1:54170 127.0.0.1:2869 ESTABLISHED TCP 192.168.1.100:49300 192.168.1.101:445 ESTABLISHED
TCP is a connection-oriented Transport layer protocol. UDP is a connectionless Transport layerprotocol.The Session LayerThe Session layer establishes conversations known as sessions between networked devices. A session is anexchange of connection-oriented transmissions between two network devices. Each of these transmissionsis handled by the Transport layer protocol. The session itself is managed by the Session layer protocol.A single session can include many exchanges of data between the two computers involved in the session.After a session between two computers has been established, it is maintained until the computers agree toterminate the session.The Session layer allows three types of transmission modes:♦ Simplex: In this mode, data flows in only one direction.♦ Half-duplex: In this mode, data flows in both directions, but only in one direction at a time.♦ Full-duplex: In this mode, data flows in both directions at the same time. In actual practice, the distinctions in the Session, Presentation, and Application layers are oftenblurred, and some commonly used protocols actually span all three layers. For example, SMB — theprotocol that is the basis of file sharing in Windows networks — functions at all three layers.The Presentation LayerThe Presentation layer is responsible for how data is represented to applications. Most computers —including Windows, Unix, and Macintosh computers — use the American Standard Code for InformationInterchange (ASCII) to represent data. However, some computers (such as IBM mainframe computers)use a different code, known as Extended Binary Coded Decimal Interchange Code (EBCDIC). ASCII andEBCDIC arent compatible with each other. To exchange information between a mainframe computer anda Windows computer, the Presentation layer must convert the data from ASCII to EBCDIC and vice versa.Besides simply converting data from one code to another, the Presentation layer can also applysophisticated compression techniques so that fewer bytes of data are required to represent theinformation when its sent over the network. At the other end of the transmission, the Presentation layerthen uncompresses the data.The Presentation layer can also scramble the data before it is transmitted and unscramble it at the otherend by using a sophisticated encryption technique that even Sherlock Holmes would have troublebreaking.The Application LayerThe highest layer of the OSI model, the Application layer, deals with the techniques that applicationprograms use to communicate with the network. The name of this layer is a little confusing. Applicationprograms such as Microsoft Office or QuickBooks arent a part of the Application layer. Rather, theApplication layer represents the programming interfaces that application programs such as MicrosoftOffice or QuickBooks use to request network services.Some of the better-known Application layer protocols are♦ DNS (Domain Name System) for resolving Internet domain names.♦ FTP (File Transfer Protocol) for file transfers.♦ SMTP (Simple Mail Transfer Protocol) for e-mail.♦ SMB (Server Message Block) for file sharing in Windows networks.♦ NFS (Network File System) for file sharing in Unix networks.♦ Telnet for terminal emulation.Following a Packet through the Layers Figure 2-5 shows how a packet of information flows through the seven layers as it travels fromone computer to another on the network. The data begins its journey when an end-user application sendsdata to another network computer. The data enters the network through an Application layer interface,
such as SMB. The data then works its way down through the protocol stack. Along the way, the protocol ateach layer manipulates the data by adding header information, converting the data into different formats,combining packets to form larger packets, and so on. When the data reaches the Physical layer protocol,its actually placed on the network media (in other words, the cable) and sent to the receiving computer.When the receiving computer receives the data, the data works its way up through the protocol stack.Then, the protocol at each layer reverses the processing that was done by the corresponding layer on thesending computer. Headers are removed, data is converted back to its original format, packets that weresplit into smaller packets are recombined into larger messages, and so on. When the packet reaches theApplication layer protocol, its delivered to an application that can process the data.Figure 2-5: How data travels through the seven layers.
The Ethernet ProtocolAs you know, the first two layers of the OSI model deal with the physical structure of the network and themeans by which network devices can send information from one device on a network to another. By far,the most popular set of protocols for the Physical and Data Link layers is Ethernet.Ethernet has been around in various forms since the early 1970s. (For a brief history of Ethernet, see thesidebar, "Ethernet folklore and mythology," later in this chapter.) The current incarnation of Ethernet isdefined by the IEEE standard known as 802.3. Various flavors of Ethernet operate at different speeds anduse different types of media. However, all the versions of Ethernet are compatible with each other, so youcan mix and match them on the same network by using devices such as bridges, hubs, and switches to linknetwork segments that use different types of media. The actual transmission speed of Ethernet is measured in millions of bits per second, or Mbps.Ethernet comes in three different speed versions: 10 Mbps, known as Standard Ethernet; 100 Mbps,known as Fast Ethernet; and 1,000 Mbps, known as Gigabit Ethernet. Keep in mind, however, thatnetwork transmission speed refers to the maximum speed that can be achieved over the network underideal conditions. In reality, the actual throughput of an Ethernet network rarely reaches this maximumspeed.Ethernet operates at the first two layers of the OSI model — the Physical and the Data Link layers.However, Ethernet divides the Data Link layer into two separate layers known as theLogical LinkControl (LLC) layer and the Medium Access Control (MAC) layer. Figure 2-6 shows how the variouselements of Ethernet match up to the OSI model.Figure 2-6: Ethernet and the OSI model.The following sections describe Standard Ethernet, Fast Ethernet, and Gigabit Ethernet in more detail.Standard EthernetStandard Ethernet is the original Ethernet. It runs at 10 Mbps, which was considered fast in the 1970s butis pretty slow by todays standards. Although there is still plenty of existing Standard Ethernet in use, it isconsidered obsolete and should be replaced by Gigabit Ethernet as soon as possible.Standard Ethernet comes in four incarnations, depending on the type of cable used to string the networktogether:♦ 10Base5: The original Ethernet cable was thick (about as thick as your thumb), heavy, and difficult towork with. Its seen today only in museums.♦ 10Base2: This thinner type of coaxial cable (it resembles television cable) became popular in the 1980sand lingered into the early 1990s. Plenty of 10Base2 cable is still in use, but its rarely installed in newnetworks. 10Base2 (like 10Base5) uses a bus topology, so wiring a 10Base2 network involves runningcable from one computer to the next until all the computers are connected in a segment.
♦ 10BaseT: Unshielded twisted-pair cable (also known as UTP) became popular in the 1990s because itseasier to install, lighter, and more reliable, and it offers more flexibility in how networks are designed.10BaseT networks use a star topology with hubs at the center of each star. Although the maximum lengthof 10BaseT cable is only 100 meters, hubs can be chained together to extend networks well beyond the100-meter limit.10BaseT cable has four pairs of wires that are twisted together throughout the entire span of the cable.However, 10BaseT uses only two of these wire pairs, so the unused pairs are spares.♦ 10BaseFL: Fiber-optic cables were originally supported at 10 Mbps by the 10BaseFL standard.However, because faster fiber-optic versions of Ethernet now exist, 10BaseFL is rarely used.Fast EthernetFast Ethernet refers to Ethernet that runs at 100 Mbps, which is ten times the speed of Standard Ethernet.The following are the three varieties of Fast Ethernet:♦ 100BaseT4: The 100BaseT4 protocol allows transmission speeds of 100 Mbps over the same UTPcable as 10BaseT networks. To do this, it uses all four pairs of wire in the cable. 100BaseT4 simplifies thetask of upgrading an existing 10BaseT network to 100 Mbps.♦ 100BaseTX: The most commonly used standard for office networks today is 100BaseTX, whichtransmits at 100 Mbps over just two pairs of a higher grade of UTP cable than the cable used by 10BaseT.The higher-grade cable is referred to as Category 5.Most new networks are wired with Category 5 orbetter cable.♦ 100BaseFX: The fiber-optic version of Ethernet running at 100 Mbps is called 100BaseFX. Becausefiber-optic cable is expensive and tricky to install, it isnt used much for individual computers in anetwork. However, its commonly used as a networkbackbone. For example, a fiber backbone is often usedto connect individual workgroup hubs to routers and servers. Ethernet folklore and mythology If youre a history buff, you may be interested in the story of how Ethernet came to be so popular. Heres how it happened: The original idea for the Ethernet was hatched in the mind of a graduate computer science student at Harvard University named Robert Metcalfe. Looking for a thesis idea in 1970, he refined a networking technique that was used in Hawaii, called the AlohaNet (it was actually a wirelessnetwork), and developed a technique that would enable a network to efficiently use as much as 90 percent of its capacity. By 1973, he had his first Ethernet network up and running at the famous Xerox Palo Alto Research Center (PARC). Bob dubbed his network "Ethernet" in honor of the thick network cable, which he called "the ether." (Xerox PARC was busy in 1973. In addition to Ethernet, PARC developed the firstpersonal computer that used a graphical user interface complete with icons, windows, and menus, and the worlds first laser printer.) In 1979, Xerox began working with Intel and DEC (a once popular computer company) to make Ethernet an industry standard networking product. Along the way, they enlisted the help of the IEEE, which formed committee number 802.3 and began the process of standardizing Ethernet in 1981. The 802.3 committee released the first official Ethernet standard in 1983.Meanwhile, Bob Metcalfe left Xerox, turned down a job offer from Steve Jobs to work at Apple computers, and started a company called the Computer, Communication, and Compatibility Corporation — now known as 3Com. 3Com has since become one of the largest manufacturers of Ethernet equipment in the world.Gigabit EthernetGigabit Ethernet is Ethernet running at a whopping 1,000 Mbps, which is 100 times faster than theoriginal 10 Mbps Ethernet. Gigabit Ethernet was once considerably more expensive than Fast Ethernet, soit was used only when the improved performance justified the extra cost. However, today Gigabit Ethernetis the standard for nearly all desktop and laptop PCs.Gigabit Ethernet comes in two flavors:♦ 1000BaseT: Gigabit Ethernet can run on Category 5 UTP cable, but higher grades such as Category 5eor Category 6 are preferred because theyre more reliable.♦ 1000BaseLX: Several varieties of fiber cable are used with Gigabit Ethernet, but the most popular iscalled 1000BaseLX.The TCP/IP Protocol Suite
TCP/IP, the protocol on which the Internet is built, is actually not a single protocol but rather an entiresuite of related protocols. TCP is even older than Ethernet. It was first conceived in 1969 by theDepartment of Defense. For more on the history of TCP/IP, see the sidebar, "The fascinating story ofTCP/IP," later in this chapter. Currently, the Internet Engineering Task Force, or IETF, manages theTCP/IP protocol suite.The TCP/IP suite is based on a four-layer model of networking that is similar to the seven-layer OSImodel. Figure 2-7 shows how the TCP/IP model matches up with the OSI model and where some of thekey TCP/IP protocols fit into the model. As you can see, the lowest layer of the model, the NetworkInterface layer, corresponds to the OSI models Physical and Data Link layers. TCP/IP can run over a widevariety of Network Interface layer protocols, including Ethernet, as well as other protocols, such as TokenRing and FDDI (an older standard for fiber-optic networks).Figure 2-7: TCP/IP and the OSI model.The Application layer of the TCP/IP model corresponds to the upper three layers of the OSI model — thatis, the Session, Presentation, and Application layers. Many protocols can be used at this level. A few of themost popular are HTTP, FTP, Telnet, SMTP, DNS, and SNMP.You can find out about many of the details of these and other TCP/IP protocols in Book IV. In thefollowing sections, I just want to point out a few more details of the three most important protocols in theTCP/IP suite: IP, TCP, and UDP.IPIP, which stands for Internet Protocol, is a Network layer protocol that is responsible for deliveringpackets to network devices. The IP protocol uses logical IP addresses to refer to individual devices ratherthan physical (MAC) addresses. A protocol called ARP (for Address Resolution Protocol) handles the taskof converting IP addresses to MAC addresses. 10Base what?The names of Ethernet cable standards resemble the audible signals a quarterback might shout at the line of scrimmage. In reality, the cable designations consist of three parts: The first number is the speed of the network in Mbps. So 10BaseT is for 10 Mbps networks (Standard Ethernet), 100BaseTX is for 100 Mbps networks (Fast Ethernet), and 1000BaseT is for 1,000 Mbps networks (Gigabit Ethernet). The word Base indicates the type of network transmission that the cable uses. Base is shortfor baseband. Baseband transmissions carry one signal at a time and are relatively simple to implement. The alternative to baseband is broadband, which can carry more than one signal at a time but is more difficult to implement. At one time, broadband incarnations of the 802.x networking standards existed, but they have all but fizzled due to lack of use.
The tail end of the designation indicates the cable type. For coaxial cables, a number is used that roughly indicates the maximum length of the cable in hundreds of meters. 10Base5 cables can run up to 500 meters. 10Base2 cables can run up to 185 meters. (The IEEE rounded 185 up to 200 to come up with the name 10Base2.) If the designation ends with a T, twisted-pair cable is used. Other letters are used for other types of cables.Because IP addresses consist of a network part and a host part, IP is a routable protocol. As a result, IPcan forward a packet to another network if the host is not on the current network. (The ability to routepackets across networks is where IP gets its name. Aninternet is a series of two or more connected TCP/IPnetworks that can be reached by routing.)TCPTCP, which stands for Transmission Control Protocol, is a connection-oriented Transport layer protocol.TCP lets a device reliably send a packet to another device on the same network or on a different network.TCP ensures that each packet is delivered if at all possible. It does so by establishing a connection with thereceiving device and then sending the packets. If a packet doesnt arrive, TCP resends the packet. Theconnection is closed only after the packet has been successfully delivered or an unrecoverable errorcondition has occurred.One key aspect of TCP is that its always used for one-to-one communications. In other words, TCP allowsa single network device to exchange data with another single network device. TCP isnt used to broadcastmessages to multiple network recipients. Instead, the User Datagram Protocol (UDP) is used for thatpurpose. The fascinating story of TCP/IP Some people are fascinated by history. They subscribe to cable TV just to get the History Channel. If youre one of those history buffs, you may be interested in the following chronicle of TCP/IPs humble origins. (For maximum effect, play some melancholy violin music in the background as you read the rest of this sidebar.) In the summer of 1969, the four mop-topped singers from Liverpool were breaking up. The war in Vietnam was escalating. Astronauts Neil Armstrong and Buzz Aldrin walked on the moon. And the Department of Defense built a computer network called ARPANET to link its defense installations with several major universities throughout the United States.By the early 1970s, ARPANET was becoming difficult to manage. So it was split into two networks: one for military use, called MILNET, and the other for nonmilitary use. The nonmilitary network retained thename ARPANET. To link MILNET with ARPANET, a new method of connecting networks, called Internet Protocol or just IP for short, was invented. The whole purpose of IP was to enable these two networks to communicate with each other. Fortunately,the designers of IP realized that it wouldnt be too long before other networks wanted to join in the fun, so they designed IP to allow for more than two networks. In fact, their ingenious design allowed for tens of thousands of networks to communicate via IP. The decision was a fortuitous one, as the Internet quickly began to grow. By the mid-1980s, the original ARPANET reached its limits. Just in time, the National Science Foundation (NSF) decided to get into the game. NSF had built a network called NSFNET to link its huge supercomputers. NSFNET replaced ARPANET as the new background for the Internet. Around that time, such magazines as Time and Newsweek began writing articles about this new phenomenon called the Internet, and the Net (as it became nicknamed) began to grow like wildfire. Soon NSFNET couldnt keep up with the growth, so several private commercial networks took over management of the Internet backbone. TheInternet has grown at a dizzying rate ever since, and nobody knows how long this frenetic growth rate will continue. One thing is sure: TCP/IP is now the most popular networking protocol in the world.Many well-known Application layer protocols rely on TCP. For example, when a user running a Webbrowser requests a page, the browser uses HTTP to send a request via TCP to the Web server. When theWeb server receives the request, it uses HTTP to send the requested Web page back to the browser, againvia TCP. Other Application layer protocols that use TCP include Telnet (for terminal emulation), FTP (forfile exchange), and SMTP (for e-mail).UDPThe User Datagram Protocol (or UDP) is a connectionless Transport layer protocol that is used when theoverhead of a connection isnt required. After UDP has placed a packet on the network (via the IPprotocol), it forgets about it. UDP doesnt guarantee that the packet actually arrives at its destination.
Most applications that use UDP simply wait for any replies expected as a result of packets sent via UDP. Ifa reply doesnt arrive within a certain period of time, the application either sends the packet again or givesup.Probably the best-known Application layer protocol that uses UDP is DNS, the Domain Name System.When an application needs to access a domain name such aswww.wiley.com, DNS sends a UDP packet toa DNS server to look up the domain. When the server finds the domain, it returns the domains IP addressin another UDP packet. (Actually, the process is much more complicated than that. For a more detailedexplanation, see Book IV, Chapter 4.)Other Protocols Worth Knowing AboutOther networks besides Ethernet, TCP/IP, and IPX/SPX are worth knowing about:♦ NetBIOS: Short for Network Basic Input/Output System, this is the basic application-programminginterface for network services on Windows computers. Its installed automatically when you installTCP/IP, but doesnt show up as a separate protocol when you view the network connection properties.(Refer to Figure 2-1.) NetBIOS is a Session layer protocol that can work with Transport layer protocolssuch as TCP, SPX, or NetBEUI.♦ NetBEUI: Short for Network BIOS Extended User Interface, this is a Transport layer protocol that wasdesigned for early IBM and Microsoft networks. NetBEUI is now considered obsolete.♦ IPX/SPX: A protocol suite that was made popular in the 1980s by Novell for use with their NetWareservers. TCP/IP has become so dominant that IPX/SPX is now only rarely used.♦ AppleTalk: Apple computers have their own suite of network protocols known asAppleTalk. TheAppleTalk suite includes a Physical and Data Link layer protocol calledLocalTalk, but can also work withstandard lower-level protocols, including Ethernet and Token Ring.♦ SNA: Systems Network Architecture is an IBM networking architecture that dates back to the 1970s,when mainframe computers roamed the earth and PCs had barely emerged from the primordial computersoup. SNA was designed primarily to support huge terminals such as airline reservation and bankingsystems, with tens of thousands of terminals attached to central host computers. Now that IBMmainframes support TCP/IP and terminal systems have all but vanished, SNA is beginning to fade away.Still, many networks that incorporate mainframe computers have to contend with SNA. Chapter 3: Understanding Network HardwareIn This Chapter Introducing servers Working with network interface cards Becoming familiar with network cable, network hubs, and switches Exploring repeaters, bridges, and routers Figuring out network storageThe building blocks of networks are network hardware devices such as servers, adapter cards, cables,hubs, switches, routers, and so on. This chapter provides an overview of these building blocks.ServersServer computers are the lifeblood of any network. Servers provide the shared resources that networkusers crave, such as file storage, databases, e-mail, Web services, and so on. Choosing the equipment youuse for your networks servers is one of the key decisions youll make when you set up a network. In thefollowing sections, I describe some of the various ways you can equip your networks servers. Right off the bat, I want to make one thing clear: Only the smallest networks can do without atleast one dedicated server computer. For a home network or a small office network with only a fewcomputers, you can get away with true peer-to-peer networking. Thats where each client computershares its resources such as file storage or printers, and a dedicated server computer isnt needed. For amore-detailed explanation of why this isnt a good idea for larger networks, see Book II, Chapter 1.Whats important in a serverHere are some general things to keep in mind when picking a server computer for your network:♦ Scalability: Scalability refers to the ability to increase the size and capacity of the server computerwithout unreasonable hassle. Its a major mistake to purchase a server computer that just meets your
current needs because, you can rest assured, your needs will double within a year. If at all possible, equipyour servers with far more disk space, RAM, and processor power than you currently need.♦ Reliability: The old adage "you get what you pay for" applies especially well to server computers. Whyspend $10,000 on a server computer when you can buy one with seemingly similar specifications at adiscount electronics store for $2,000?One reason is reliability. When a client computer fails, only the person who uses that computer is affected.When a server fails, however, everyone on the network is affected. The less-expensive computer isprobably made of inferior components that are more likely to fail.♦ Availability: This concept of availability is closely related to reliability. When a server computer fails,how long does it take to correct the problem and get the server up and running again? Server computersare designed so their components can be easily diagnosed and replaced, which minimizes the downtimethat results when a component fails. In some servers, components are hot swappable, which means thatcertain components can be replaced without shutting down the server. Some servers are designed tobe fault-tolerantso that they can continue to operate even if a major component fails.♦ Service and support: Service and support are factors often overlooked when picking computers. If acomponent in a server computer fails, do you have someone on site qualified to repair the brokencomputer? If not, you should get an on-site maintenance contract for the computer. Dont settle for amaintenance contract that requires you to take the computer in to a repair shop or, worse, mail it to arepair facility. You cant afford to be without your server that long.Components of a server computerThe hardware components that comprise a typical server computer are similar to the components used inless expensive client computers. However, server computers are usually built from higher-gradecomponents than client computers for the reasons given in the preceding section. The followingparagraphs describe the typical components of a server computer:♦ Motherboard: The motherboard is the computers main electronic circuit board to which all the othercomponents of your computer are connected. More than any other component, the motherboard is thecomputer. All other components attach to the motherboard.The major components on the motherboard include the processor (or CPU), supporting circuitry calledthe chipset, memory, expansion slots, a standard IDE hard drive controller, and I/O ports for devices suchas keyboards, mice, and printers. Some motherboards also include additional built-in features such as agraphic adapter, SCSI disk controller, or network interface.♦ Processor: The processor, or CPU, is the brain of the computer. Although the processor isnt the onlycomponent that affects overall system performance, its the one that most people think of first whendeciding what type of server to purchase. At the time of this writing, Intel had two processor modelsspecifically designed for use in server computers, as summarized in Table 3-1.Each motherboard is designed to support a particular type of processor. CPUs come in two basicmounting styles: slot or socket. However, you can choose from several types of slots and sockets, so youhave to make sure that the motherboard supports the specific slot or socket style used by the CPU. Someserver motherboards have two or more slots or sockets to hold two or more CPUs. The term clock speed refers to how fast the basic clock that drives the processors operationticks. In theory, the faster the clock speed, the faster the processor. However, clock speed alone is reliableonly for comparing processors within the same family. In fact, the Itanium processors are faster thanXeon processors at the same clock speed. Thats because the Itanium processor models contain moreadvanced circuitry than the older model, so they can accomplish more work with each tick of the clock.The number of processor cores also has a dramatic effect on performance. Each processor core acts as ifits a separate processor. Most server computers use dual-core (two processor cores) or quad-core (fourcores) chips.
♦ Memory: Dont scrimp on memory. People rarely complain about servers having too much memory.Many different types of memory are available, so you have to pick the right type of memory to match thememory supported by your motherboard. The total memory capacity of the server depends on themotherboard. Most new servers can support at least 16GB of memory, and some can handle up to 256GB.♦ Hard drives: Most desktop computers use inexpensive hard drives called SATA drives.These drives areadequate for individual users, but because performance is more important for servers, another type ofdrive known as SCSI is usually used instead. For the best performance, use the SCSI drives along with ahigh-performance SCSI controller card. (However, because of its low cost, SATA drives are often used ininexpensive servers.)♦ Network connection: The network connection is one of the most important parts of any server. Manyservers have network adapters built into the motherboard. If your server isnt equipped as such, youllneed to add a separate network adapter card. See the section, "Network Interface Cards," later in thischapter, for more information.♦ Video: Fancy graphics arent that important for a server computer. You can equip your servers withinexpensive generic video cards and monitors without affecting network performance. (This is one of thefew areas where its acceptable to cut costs on a server.)♦ Power supply: Because a server usually has more devices than a typical desktop computer, it requiresa larger power supply (typically 300 watts). If the server houses a large number of hard drives, it mayrequire an even larger power supply.Server form factorsThe term form factor refers to the size, shape, and packaging of a hardware device. Server computerstypically come in one of three form factors:♦ Tower case: Most servers are housed in a traditional tower case, similar to the tower cases used fordesktop computers. A typical server tower case is 18-inches high, 20-inches deep, and 9-inches wide andhas room inside for a motherboard, five or more hard drives, and other components. Tower cases alsocome with built-in power supplies.Some server cases include advanced features specially designed for servers, such as redundant powersupplies (so both servers can continue operating if one of the power supplies fails), hot-swappable fans,and hot-swappable disk drive bays. (Hot-swappablecomponents can be replaced without powering downthe server.)♦ Rack mount: If you need only a few servers, tower cases are fine. You can just place the servers next toeach other on a table or in a cabinet thats specially designed to hold servers. If you need more than a fewservers, though, space can quickly become an issue. For example, what if your departmental networkrequires a bank of ten file servers? Youd need a pretty long table.Rack-mount servers are designed to save space when you need more than a few servers in a confined area.A rack-mount server is housed in a small chassis thats designed to fit into a standard 19-inch equipmentrack. The rack allows you to vertically stack servers in order to save space.♦ Blade servers: Blade servers are designed to save even more space than rack-mount servers. A bladeserver is a server on a single card that can be mounted alongside other blade servers in a blade chassis,which itself fits into a standard 19-inch equipment rack. A typical blade chassis holds six or more servers,depending on the manufacturer.One of the key benefits of blade servers is that you dont need a separate power supply for each server.Instead, the blade enclosure provides power for all its blade servers. Some blade server systems providerack-mounted power supplies that can serve several blade enclosures mounted in a single rack.
In addition, the blade enclosure provides KVM switching so that you dont have to use a separate KVMswitch. You can control any of the servers in a blade server network from a single keyboard, monitor, andmouse. (For more information, see the sidebar, "Saving space with a KVM switch.")One of the biggest benefits of blade servers is that they drastically cut down the amount of cable clutter.With rack-mount servers, each server requires its own power cable, keyboard cable, video cable, mousecable, and network cables. With blade servers, a single set of cables can service all the servers in a bladeenclosure. Saving space with a KVM switch If you have more than two or three servers in one location, you should consider getting a device called a KVM switch to save space. A KVM switch lets you connect several server computers to a singlekeyboard, monitor, and mouse. (KVM stands for keyboard, video, and mouse.) Then, you can control anyof the servers from a single keyboard, monitor, and mouse by turning a dial or by pressing a button on the KVM switch. Simple KVM switches are mechanical affairs that let you choose from among 2 to 16 or more computers. More elaborate KVM switches can control more computers, using a pop-up menu or a special keyboard combination to switch among computers. Some advanced KVMs can even control a mix of PCs and Macintosh computers from a single keyboard, monitor, and mouse. To find more information about KVM switches, go to a Web search engine such as Google and search for "KVM."Network Interface CardsEvery computer on a network, both clients and servers, requires a network interface card (or NIC) inorder to access the network. A NIC is usually a separate adapter card that slides into one of the serversmotherboard expansion slots. However, most newer computers have the NIC built into the motherboard,so a separate card isnt needed.For client computers, you can usually get away with using the inexpensive built-in NIC because clientcomputers are used to connect only one user to the network. However, the NIC in a server computerconnects many network users to the server. As a result, it makes sense to spend more money on a higher-quality NIC for a heavily used server. Most network administrators prefer to use name-brand cards frommanufacturers such as Intel, SMC, or 3Com.Most NICs made today support 1 Gbps networking and will also support slower 100 Mbps and evenancient 10 Mbps networks. These cards automatically adjust their speed to match the speed of thenetwork. So you can use a gigabit card on a network that has older 100 Mbps cards without trouble. Youcan find inexpensive gigabit cards for as little as $5 each, but a typical name-brand card (such as Linksysor Intel) will cost around $25 or $30.Here are a few other points to ponder concerning network interface cards:♦ A NIC is a Physical layer and Data Link layer device. Because a NIC establishes a network node, it musthave a physical network address, also known as a MAC address. The MAC address is burned into the NICat the factory, so you cant change it. Every NIC ever manufactured has a unique MAC address.♦ For server computers, it makes sense to use more than one NIC. That way, the server can handle morenetwork traffic. Some server NICs have two or more network interfaces built into a single card.♦ Fiber-optic networks also require NICs. Fiber-optic NICs are still too expensive for desktop use in mostnetworks. Instead, theyre used for high-speed backbones. If a server connects to a high-speed fiberbackbone, it will need a fiber-optic NIC that matches the fiber-optic cable being used.Network CableNearly all modern networks are constructed using a type of cable called twisted-pair cable, which looks alittle like phone cable but is subtly different.You may encounter other types of cable in an existing network: coax cable that resembles TV cable, thickyellow cable that used to be the only type of cable used for Ethernet, fiber-optic cables that span longdistances at high speeds, or thick twisted-pair bundles that carry multiple sets of twisted-pair cablebetween wiring closets in a large building. But as I mentioned, its twisted-pair cable for nearly all newnetworks.
A choice thats becoming more popular every day is to forego network cable and instead buildyour network using wireless network components. Because Book V is devoted exclusively to wirelessnetworking, I dont describe wireless network components in this chapter.Coaxial cableA type of cable that was once popular for Ethernet networks is coaxial cable, sometimescalled thinnet or BNC cable because of the type of connectors used on each end of the cable. Thinnet cableoperates only at 10 Mbps and is rarely used for new networks. However, youll find plenty of existingthinnet networks still being used. Figure 3-1 shows a typical coaxial cable.Figure 3-1: Coax cable.Here are some salient points about coaxial cable:♦ You attach thinnet to the network interface card by using a goofy twist-on connector called a BNCconnector. You can purchase preassembled cables with BNC connectors already attached in lengths of 25or 50 feet, or you can buy bulk cable on a big spool and attach the connectors yourself by using a specialtool. (I suggest buying preassembled cables. Attaching connectors to bulk cable can be tricky.)♦ With coaxial cables, you connect your computers point-to-point in a bus topology. At each computer, a Tconnector is used to connect two cables to the network interface card.♦ A special plug called a terminator is required at each end of a series of thinnet cables. The terminatorprevents data from spilling out the end of the cable and staining the carpet.♦ The cables strung end-to-end from one terminator to the other are collectively called asegment. Themaximum length of a thinnet segment is about 200 meters (actually, 185 meters). You can connect asmany as 30 computers on one segment. To span a distance greater than 185 meters or to connect morethan 30 computers, you must use two or more segments with a device called a repeater to connect eachsegment.
♦ Although Ethernet coaxial cable resembles TV coaxial cable, the two types of cable arentinterchangeable. Dont try to cut costs by wiring your network with cheap TV cable.Twisted-pair cableThe most popular type of cable today is twisted-pair cable, or UTP. (The U stands for unshielded, but noone says unshielded twisted pair. Just twisted pair will do.) UTP cable is even cheaper than thin coaxialcable, and best of all, many modern buildings are already wired with twisted-pair cable because this typeof wiring is often used with modern phone systems. Figure 3-2 shows a twisted-pair cable.Figure 3-2: Twisted-pair cable.When you use UTP cable to construct an Ethernet network, you connect the computers in a stararrangement. In the center of the star is a device called a hub. Depending on the model, Ethernet hubsenable you to connect from 4 to 24 computers using twisted-pair cable.An advantage of UTPs star arrangement is that if one cable goes bad, only the computer attached to thatcable is affected; the rest of the network continues to chug along. With coaxial cable, a bad cable affectsthe entire network, and not just the computer to which the bad cable is connected.Here are a few other details that you should know about twisted-pair cabling:♦ UTP cable consists of pairs of thin wire twisted around each other; several such pairs are gathered upinside an outer insulating jacket. Ethernet uses two pairs of wires, or four wires altogether. The number ofpairs in a UTP cable varies, but its often more than two.♦ UTP cable comes in various grades called Categories. Dont use anything less than Category 5e cable foryour network. Although cheaper, it may not be able to support faster networks.Although higher-Category cables are more expensive than lower-Category cables, the real cost of installingEthernet cabling is the labor required to actually pull the cables through the walls. As a result, Irecommend that you always spend the extra money to buy Category 5e cable.♦ If you want to sound like you know what youre talking about, say "Cat 5e" instead of "Category 5e." ♦ Many existing networks are cabled with Category 5 cable, which is fine for 100Mbps networksbut isnt rated for Gigabit networks. Category 5e cable (the e stands for enhanced) and Category 6 cablewill support 1,000 Mbps networks.♦ UTP cable connectors look like modular phone connectors but are a bit larger. UTP connectors areofficially called RJ-45 connectors.♦ Like thinnet cable, UTP cable is also sold in prefabricated lengths. However, RJ-45 connectors are mucheasier to attach to bulk UTP cable than BNC cables are to attach to bulk coaxial cable. As a result, I suggest
that you buy bulk cable and connectors unless your network consists of just two or three computers. Abasic crimp tool to attach the RJ-45 connectors costs about $50.♦ The maximum allowable cable length between the hub and the computer is 100 meters (about 328 feet).SwitchesThe biggest difference between using coaxial cable and twisted-pair cable is that when you use twisted-pair cable, you also must use a separate device called a switch. Years ago, switches were expensive devices— expensive enough that most do-it-yourself networkers who were building small networks opted forthinnet cable in order to avoid the expense and hassle of using hubs.Nowadays, the cost of switches has dropped so much that the advantages of twisted-pair cabling outweighthe hassle and cost of using switches. With twisted-pair cabling, you can more easily add new computersto the network, move computers, find and correct cable problems, and service the computers that youneed to remove from the network temporarily.Note that in some older networks, you may see a device known as a hub used instead of a switch. Hubsused to be used because they were less expensive than switches. However, the cost of switches came downdramatically, pushing hubs into relic status. If you have an older network that uses hubs and seems to runslowly, you can probably improve the networks speed by replacing the older hubs with newer switches.For more information, see the sidebar, "Hubs and switches demystified," later in this chapter. Hubs and switches demystified Both hubs and switches let you connect multiple computers to a twisted-pair network. Switches are more efficient than hubs, but not just because theyre faster. If you really want to know, heres the actual difference between a hub and a switch: In a hub, every packet that arrives at the hub on any of its ports is automatically sent out on every other port. The hub has to do this because its a Physical layer device, so it has no way to keep track of which computer is connected to each port. For example, suppose that Johns computer is connected to port 1 on an 8-port hub, and Andreas computer is connected to port 5. If Johns computer sends a packet of information to Andreas computer, the hub receives the packet on port 1 and then sends it out on ports 2-8. All the computers connected to the hub get to see the packet so that they can determine whether the packet was intended for them. A switch is a Data Link layer device, which means its able to look into the packets that pass through it to examine a critical piece of Data Link layer information: the MAC address. With this information in hand, a switch can keep track of which computer is connected to each of its ports. So if Johns computer on port 1 sends a packet to Andreas computer on port 5, the switch receives the packet on port 1 and then sends the packet out on port 5 only. This process is not only faster, but also improves the security of the system because other computers dont see packets that arent meant for them.If you use twisted-pair cabling, you need to know some of the ins and outs of using hubs:♦ Because you must run a cable from each computer to the switch, find a central location for the switch towhich you can easily route the cables.♦ The switch requires electrical power, so make sure that an electrical outlet is handy.♦ When you purchase a switch, purchase one with at least twice as many connections as you need. Dontbuy a four-port switch if you want to network four computers because when (not if) you add the fifthcomputer, you have to buy another switch.♦ You can connect switches to one another, as shown in Figure 3-3; this is called daisy chaining. Whenyou daisy chain switches, you connect one end of a cable to a port on one switch and the other end to aport on the other switch. Note that on some switches, you must use a special designated port for daisychaining. So be sure to read the instructions that come with the switch to make sure that you daisy chain itproperly.Figure 3-3: Daisy chaining switches together.
♦ You can daisy chain no more than three switches together. If you have more computers than three hubscan accommodate, dont panic. For a small additional cost, you can purchase hubs that have a BNCconnection on the back. Then you can string the hubs together using thinnet cable. The three-hub limitdoesnt apply when you use thinnet cable to connect the hubs. You can also get stackable switches thathave high-speed direct connections that enable two or more switches to be counted as a single switch.♦ When you shop for network hubs, you may notice that the expensive ones have network-managementfeatures that support something called SNMP. These hubs are calledmanaged hubs. Unless your networkis very large and you know what SNMP is, dont bother with the more expensive managed hubs. Youd bepaying for a feature that you may never use.♦ For large networks, you may want to consider using a managed switch. A managed switch allows you tomonitor and control various aspects of the switchs operation from a remote computer. The switch canalert you when something goes wrong with the network, and it can keep performance statistics so that youcan determine which parts of the network are heavily used and which arent. A managed switch costs twoor three times as much as an unmanaged switch, but for larger networks, the benefits of managedswitches are well worth the additional cost.RepeatersA repeater (sometimes called an extender) is a gizmo that gives your network signals a boost so that thesignals can travel farther. Its kind of like a Gatorade station in a marathon. As the signals travel past therepeater, they pick up a cup of Gatorade, take a sip, splash the rest of it on their heads, toss the cup, andhop in a cab when theyre sure that no one is looking.You need a repeater when the total length of a single span of network cable exceeds 100 meters (328 feet).The 100-meter length limit applies to the cable that connects a computer to the switch or the cable thatconnects switches to each other when switches are daisy chained together. In other words, you canconnect each computer to the switch with no more than 100 meters of cable, and you can connect switchesto each other with no more than 100 meters of cable.Figure 3-4 shows how you can use a repeater to connect two groups of computers that are too far apart tobe strung on a single segment. When you use a repeater like this, the repeater divides the cable into twosegments. The cable length limit still applies to the cable on each side of the repeater.Here are some points to ponder when you lie awake tonight wondering about repeaters:♦ Repeaters are not typically used with twisted-pair networks.Well, technically, thats not true because the switches themselves function as repeaters. So what I reallymeant is that you typically see repeaters as stand-alone devices only when a single cable segment wouldbe more than 100 meters.♦ A basic rule of Ethernet life is that a signal cant pass through more than three repeaters on its way fromone node to another. That doesnt mean you cant have more than three repeaters or switches, but if youdo, you have to carefully plan the network cabling so that the three-repeater rule isnt violated.♦ Repeaters are legitimate components of a by-the-book Ethernet network. They dont extend themaximum length of a single segment; they just enable you to tie two segments together. Beware of thelittle black boxes that claim to extend the segment limit beyond the standard 100-meter limit for10/100BaseT cable. These products usually work, but playing by the rules is better.Figure 3-4: Using a repeater.
BridgesA bridge is a device that connects two networks so that they act as if theyre one network. Bridges are usedto partition one large network into two smaller networks for performance reasons. You can think of abridge as a kind of smart repeater.Repeaters listen to signals coming down one network cable, amplify them, and send them down the othercable. They do this blindly, paying no attention to the content of the messages that they repeat.In contrast, a bridge is a little smarter about the messages that come down the pike. For starters, mostbridges have the capability to listen to the network and automatically figure out the address of eachcomputer on both sides of the bridge. Then the bridge can inspect each message that comes from one sideof the bridge and broadcast it on the other side of the bridge, but only if the message is intended for acomputer thats on the other side.This key feature enables bridges to partition a large network into two smaller, more efficient networks.Bridges work best in networks that are highly segregated. For example (humor me here — Im a Dr. Seussfan), suppose that the Sneetches networked all their computers and discovered that, although the Star-Bellied Sneetches computers talked to each other frequently and the Plain-Bellied Sneetches computersalso talked to each other frequently, rarely did a Star-Bellied Sneetchs computer talk to a Plain-BelliedSneetchs computer.
A bridge can partition the Sneetchnet into two networks: the Star-Bellied network and the Plain-Belliednetwork. The bridge automatically learns which computers are on the Star-Bellied network and which areon the Plain-Bellied network. The bridge forwards messages from the Star-Bellied side to the Plain-Belliedside (and vice versa) only when necessary. The overall performance of both networks improves, althoughthe performance of any network operation that has to travel over the bridge slows down a bit.Here are a few additional things to consider about bridges:♦ Some bridges also have the capability to translate the messages from one format to another. Forexample, if the Star-Bellied Sneetches build their network with Ethernet and the Plain-Bellied Sneetchesuse Token Ring, a bridge can tie the two together.♦ You can get a basic bridge to partition two Ethernet networks for about $500 from mail order suppliers.More sophisticated bridges can cost as much as $5,000 or more.♦ For simple bridge applications, you dont need an expensive specialized bridge device; instead, you canjust use a switch. Thats because a switch is effectively a multi-port bridge.♦ If youve never read Dr. Seusss classic story of the Sneetches, you should.RoutersA router is like a bridge, but with a key difference. Bridges are Data Link layer devices, so they can tell theMAC address of the network node to which each message is sent, and can forward the message to theappropriate segment. However, they cant peek into the message itself to see what type of information isbeing sent. In contrast, a router is a Network layer device, so it can work with the network packets at ahigher level. In particular, a router can examine the IP address of the packets that pass through it. Andbecause IP addresses have both a network and a host address, a router can determine what network amessage is coming from and going to. Bridges are ignorant of this information.One key difference between a bridge and a router is that a bridge is essentially transparent to the network.In contrast, a router is itself a node on the network, with its own MAC and IP addresses. This means thatmessages can be directed to a router, which can then examine the contents of the message to determinehow it should handle the message.You can configure a network with several routers that can work cooperatively together. For example, somerouters are able to monitor the network to determine the most efficient path for sending a message to itsultimate destination. If a part of the network is extremely busy, a router can automatically route messagesalong a less-busy route. In this respect, the router is kind of like a traffic reporter up in a helicopter. Therouter knows that the 101 is bumper-to-bumper all the way through Sunnyvale, so it sends the message on280 instead.Heres some additional information about routers:♦ The functional distinctions between bridges and routers — and switches and hubs, for that matter — getblurrier all the time. As bridges, hubs, and switches become more sophisticated, theyre able to take onsome of the chores that used to require a router, thus putting many routers out of work.♦ Some routers are nothing more than computers with several network interface cards and specialsoftware to perform the router functions.♦ Routers can also connect networks that are geographically distant from each other via a phone line(using modems) or ISDN.♦ You can also use a router to join your LAN to the Internet. Figure 3-5 shows a router used for thispurpose.Figure 3-5: Connecting to the Internet with a router.
Network Attached StorageMany network servers exist solely for the purpose of making disk space available to network users. Asnetworks grow to support more users, and users require more disk space, network administrators areconstantly finding ways to add more storage to their networks. One way to do that is to add more fileservers. However, a simpler and less expensive way is to use network attached storage, also known asNAS.A NAS device is a self-contained file server thats preconfigured and ready to run. All you have to do to setit up is take it out of the box, plug it in, and turn it on. NAS devices are easy to set up and configure, easyto maintain, and less expensive than traditional file servers. NAS should not be confused with a related technology called storage area networks, or SAN.SAN is a much more complicated and expensive technology that provides huge quantities of data storagefor large networks. For more information on SAN, see the sidebar, "SAN is NAS spelled backwards."A typical entry-level NAS device is the Dell PowerVault NX300. This device is a self-contained file serverbuilt into a small rack-mount chassis. It supports up to four hard drives with a total capacity up to fourterabyte (or 4,000GB). The NX300 uses a Xeon processor and two built-in gigabit network ports. SAN is NAS spelled backwards
Its easy to confuse the terms storage area network (SAN) and network attached storage(NAS). Both refer to relatively new network technologies that let you manage the disk storage on your network. However, NAS is a much simpler and less expensive technology. A NAS device is nothing more than aninexpensive self-contained file server. Using NAS devices actually simplifies the task of adding storage to a network because the NAS eliminates the chore of configuring a network operating system for routine file- sharing tasks. A storage area network is designed for managing very large amounts of network storage — sometimes downright huge amounts. A SAN consists of three components: storage devices (perhaps hundreds of them), a separate high-speed network (usually fiber-optic) that directly connects the storage devices to each other, and one or more SAN servers that connect the SAN to the local area network. The SAN server manages the storage devices attached to the SAN and allows users of the LAN to access the storage. Setting up and managing a storage area network is a job for a SAN expert. For more information about storage area networks, see the home page of the Storage Networking Industry Association at www.snia.org.The Dell NX300 runs a special version of Windows Server 2008 called the Windows Storage Server 2008.This version of Windows is designed specifically for NAS devices. It allows you to configure the networkstorage from any computer on the network by using a Web browser.Note that some NAS devices use customized versions of Linux rather than Windows Storage Server. Also,in some systems, the operating system resides on a separate hard drive thats isolated from the shareddisks. This prevents the user from inadvertently damaging the operating system.Network PrintersAlthough you can share a printer on a network by attaching the printer to a server computer, manyprinters have network interfaces built in. This lets you connect the printer directly to the network. Thennetwork users can connect to the printer and use it without going through a server.Even if you connect a printer directly to the network, its still a good idea to have the printer managed by aserver computer running a network operating system such as Windows Server 2003 or 2007. That way,the server can store print jobs sent to the printer by multiple users and print the jobs in the order in whichthey were received. Chapter 4: Understanding Network Operating SystemsIn This Chapter Understanding what network operating systems do Figuring out the advantages of Windows Server 2003 Analyzing Windows 2000 Server Taking a look at Windows NT Server Navigating NetWare Delving into peer-to-peer networking Exploring other network operating systemsOne of the basic choices that you must make before you proceed any further is to decide which networkoperating system (NOS) to use as the foundation for your network. This chapter begins with a descriptionof several important features found in all network operating systems. Next, it provides an overview of theadvantages and disadvantages of the most popular network operating systems.Network Operating System FeaturesAll network operating systems, from the simplest to the most complex, must provide certain corefunctions. These include the ability to connect to other computers on the network, share files and otherresources, provide for security, and so on. In the following sections, I describe some of these core NOSfeatures in general terms.Network supportIt goes without saying that a network operating system should support networks. (I can picture MikeMyers in his classic Saturday Night Live role as Linda Richman, host ofCoffee Talk, saying "Im getting alittle verklempt. . . . Talk amongst yourselves. . . . Ill give you a topic — network operating systems do notnetwork, nor do they operate. Discuss.")A network operating system must support a wide variety of networking protocols in order to meet theneeds of its users. Thats because a large network typically consists of a mixture of various versions of
Windows, as well as a few scattered Macintosh (mostly in the art department) and possibly some Linuxcomputers. The computers often have distinct protocols.Many servers have more than one network interface card installed. In that case, the NOS must be able tosupport multiple network connections. Ideally, the NOS should have the ability to balance the networkload among its network interfaces. In addition, in the event that one of the connections fails, the NOSshould be able to seamlessly switch to another connection.Finally, most network operating systems include a built-in ability to function as a router that connects twonetworks. The NOS router functions should also include firewall features in order to keep unauthorizedpackets from entering the local network.File-sharing servicesOne of the most important functions of a network operating system is its ability to share resources withother network users. The most common resource thats shared is the servers file system. A network servermust be able to share some or all of its disk space with other users so that those users can treat theservers disk space as an extension of their own computers disk spaces.The NOS allows the system administrator to determine which portions of the servers file system to share.Although an entire hard drive can be shared, it isnt commonly done. Instead, individual directories orfolders are shared. The administrator can control which users are allowed to access each shared folder.Because file sharing is the reason many network servers exist, network operating systems have moresophisticated disk management features than are found in desktop operating systems. For example, mostnetwork operating systems have the ability to manage two or more hard drives as if they were a singledrive. In addition, most can create mirrors, which automatically keep backup copies of drives on a seconddrive.MultitaskingOnly one user at a time uses a desktop computer; however, multiple users simultaneously use servercomputers. As a result, a network operating system must provide support for multiple users who accessthe server remotely via the network.At the heart of multiuser support is multitasking, which is the ability of an operating system to executemore than one program — called a task or a process — at a time. Multitasking operating systems are likethe guy who used to spin plates balanced on sticks on the old Ed Sullivan Show. Hed run from plate toplate, trying to keep them all spinning so they wouldnt fall off the sticks. To make it challenging, hed do itblindfolded or riding on a unicycle.Although multitasking creates the appearance that two or more programs are executing on the computerat one time, in reality, a computer with a single processor can execute only one program at a time. Theoperating system switches the CPU from one program to another to create the appearance that severalprograms are executing simultaneously, but at any given moment, only one of the programs is actuallyexecuting. The others are patiently waiting for their turns. (However, if the computer has more than oneCPU, the CPUs can execute programs simultaneously, which is called multiprocessing.)To see multitasking in operation on a Windows computer, press Ctrl+Alt+Delete to bring up the WindowsTask Manager and then click the Processes tab. All the tasks currently active on the computer appear.For multitasking to work reliably, the network operating system must completely isolate the executingprograms from each other. Otherwise, one program may perform an operation that adversely affectsanother program. Multitasking operating systems do this by providing each task with its ownunique address space that makes it almost impossible for one task to affect memory that belongs toanother task. In most cases, each program executes as a single task or process within the memory addressspace allocated to the task. However, a single program can also be split into several tasks. This techniqueis usually called multithreading, and the programs tasks are called threads. The two approaches to multitasking are preemptive and non-preemptive. Inpreemptivemultitasking, the operating system decides how long each task gets to execute before it should step asideso that another task can execute. When a tasks time is up, the operating systems task manager interrupts
the task and switches to the next task in line. All the network operating systems in widespread use todayuse preemptive multitasking.The alternative to preemptive multitasking is non-preemptive multitasking. In non-preemptivemultitasking, each task that gets control of the CPU is allowed to run until it voluntarily gives up controlso that another task can run. Non-preemptive multitasking requires less operating system overheadbecause the operating system doesnt have to keep track of how long each task has run. However,programs have to be carefully written so that they dont hog the computer all to themselves.Directory servicesDirectories are everywhere. When you need to make a phone call, you look up the number in a phonedirectory. When you need to find the address of a client, you look up his or her name in your Rolodex. Andwhen you need to find the Sam Goody store at a shopping mall, you look for the mall directory.Networks have directories, too. Network directories provide information about the resources that areavailable on the network, such as users, computers, printers, shared folders, and files. Directories are anessential part of any network operating system.
Contents at a GlanceIntroductionCHAPTER 1 Introducing Computer NetworksCHAPTER 2 Dissecting the OSI ModelCHAPTER 3 Identifying Network ComponentsCHAPTER 4 Understanding EthernetCHAPTER 5 Working with IP AddressesCHAPTER 6 Routing TrafficCHAPTER 7 Introducing Wide-Area NetworksCHAPTER 8 Connecting WirelesslyCHAPTER 9 Optimizing Network PerformanceCHAPTER 10 Using Command-Line UtilitiesCHAPTER 11 Managing a NetworkCHAPTER 12 Securing a NetworkCHAPTER 13 Troubleshooting Network IssuesCHAPTER 14 Final PreparationAPPENDIX A Answers to Review QuestionsAPPENDIX B CompTIA Network+ N10-005 Exam Updates, Version 1.0GlossaryIndexAPPENDIX C Memory Tables (DVD Only)APPENDIX D Memory Table Answer Key (DVD Only)Table of ContentsIntroductionChapter 1 Introducing Computer NetworksFoundation TopicsDefining a NetworkThe Purpose of NetworksOverview of Network ComponentsNetworks Defined by GeographyLANWANOther Categories of NetworksCANMANPANNetworks Defined by TopologyPhysical Versus Logical TopologyBus TopologyRing Topology
Star TopologyHub-and-Spoke TopologyFull-Mesh TopologyPartial-Mesh TopologyNetworks Defined by Resource LocationClient-Server NetworksPeer-to-Peer NetworksSummaryExam Preparation TasksReview All the Key TopicsComplete Tables and Lists from MemoryDefine Key TermsReview QuestionsChapter 2 Dissecting the OSI ModelFoundation TopicsThe Purpose of Reference ModelsThe OSI ModelLayer 1: The Physical LayerLayer 2: The Data Link LayerMedia Access ControlLogical Link ControlLayer 3: The Network LayerLayer 4: The Transport LayerLayer 5: The Session LayerLayer 6: The Presentation LayerLayer 7: The Application LayerThe TCP/IP StackLayers of the TCP/IP StackCommon Application Protocols in the TCP/IP StackSummaryExam Preparation TasksReview All the Key TopicsComplete Tables and Lists from MemoryDefine Key TermsReview QuestionsChapter 3 Identifying Network ComponentsFoundation TopicsMediaCoaxial CableTwisted-Pair CableShielded Twisted PairUnshielded Twisted Pair
Plenum Versus Non-Plenum CableFiber-Optic CableMultimode FiberSingle-Mode FiberCable DistributionWireless TechnologiesNetwork Infrastructure DevicesHubsBridgesSwitchesMultilayer SwitchesRoutersInfrastructure Device SummarySpecialized Network DevicesVPN ConcentratorsFirewallsDNS ServersDHCP ServersProxy ServersContent EnginesContent SwitchesVirtual Network DevicesVirtual ServersVirtual SwitchesVirtual DesktopsOther Virtualization SolutionsVoice over IP Protocols and ComponentsSummaryExam Preparation TasksReview All the Key TopicsComplete Tables and Lists from MemoryDefine Key TermsReview QuestionsChapter 4 Understanding EthernetFoundation TopicsPrinciples of EthernetEthernet OriginsCarrier Sense Multiple Access Collision DetectDistance and Speed LimitationsEthernet Switch FeaturesVirtual LANsTrunks
Spanning Tree ProtocolCorruption of a Switch’s MAC Address TableBroadcast StormsSTP OperationLink AggregationPower over EthernetPort MonitoringUser AuthenticationFirst-Hop RedundancyOther Switch FeaturesSummaryExam Preparation TasksReview All the Key TopicsComplete Tables and Lists from MemoryDefine Key TermsReview QuestionsChapter 5 Working with IP AddressesFoundation TopicsBinary NumberingPrinciples of Binary NumberingConverting a Binary Number to a Decimal NumberConverting a Decimal Number to a Binary NumberBinary Numbering PracticeBinary Conversion Exercise #1Binary Conversion Exercise #1: SolutionBinary Conversion Exercise #2Binary Conversion Exercise #2: SolutionBinary Conversion Exercise #3Binary Conversion Exercise #3: SolutionBinary Conversion Exercise #4Binary Conversion Exercise #4: SolutionIPv4 AddressingIPv4 Address StructureClasses of AddressesTypes of AddressesUnicastBroadcastMulticastAssigning IPv4 AddressesIP Addressing ComponentsStatic ConfigurationDynamic Configuration
BOOTPDHCPAutomatic Private IP AddressingSubnettingPurpose of SubnettingSubnet Mask NotationSubnet Notation: Practice Exercise #1Subnet Notation: Practice Exercise #1 SolutionSubnet Notation: Practice Exercise #2Subnet Notation: Practice Exercise #2 SolutionExtending a Classful MaskBorrowed BitsCalculating the Number of Created SubnetsCalculating the Number of Available HostsBasic Subnetting Practice: Exercise #1Basic Subnetting Practice: Exercise #1 SolutionBasic Subnetting Practice: Exercise #2Basic Subnetting Practice: Exercise #2 SolutionCalculating New IP Address RangesAdvanced Subnetting Practice: Exercise #1Advanced Subnetting Practice: Exercise #1 SolutionAdvanced Subnetting Practice: Exercise #2Advanced Subnetting Practice: Exercise #2 SolutionAdditional PracticeClassless Inter-Domain RoutingIP Version 6Need for IPv6IPv6 Address StructureIPv6 Data FlowsUnicastMulticastAnycastSummaryExam Preparation TasksReview All the Key TopicsComplete Tables and Lists from MemoryDefine Key TermsReview QuestionsChapter 6 Routing TrafficFoundation TopicsBasic Routing ProcessesSources of Routing Information
Directly Connected RoutesStatic RoutesDynamic Routing ProtocolsRouting Protocol CharacteristicsBelievability of a RouteMetricsInterior Versus Exterior Gateway ProtocolsRoute Advertisement MethodDistance VectorLink StateRouting Protocol ExamplesAddress TranslationNATPATMulticast RoutingIGMPPIMPIM-DMPIM-SMSummaryExam Preparation TasksReview All the Key TopicsComplete Tables and Lists from MemoryDefine Key TermsReview QuestionsChapter 7 Introducing Wide-Area NetworksFoundation TopicsWAN PropertiesWAN Connection TypesWAN Data RatesWAN Media TypesPhysical MediaWireless MediaWAN TechnologiesDedicated Leased LineT1E1T3E3CSU/DSUPoint-to-Point ProtocolDigital Subscriber Line
Cable ModemSynchronous Optical NetworkSatellitePlain Old Telephone ServiceIntegrated Services Digital NetworkFrame RelayAsynchronous Transfer ModeMultiprotocol Label SwitchingSummaryExam Preparation TasksReview All the Key TopicsComplete Tables and Lists from MemoryDefine Key TermsReview QuestionsChapter 8 Connecting WirelesslyFoundation TopicsIntroducing Wireless LANsWLAN Concepts and ComponentsWireless RoutersWireless Access PointAntennasFrequencies and ChannelsCSMA/CATransmission MethodsWLAN Standards802.11a802.11b802.11g802.11nDeploying Wireless LANsTypes of WLANsIBSSBSSESSSources of InterferenceWireless AP PlacementSecuring Wireless LANsSecurity IssuesApproaches to WLAN SecuritySecurity StandardsWEPWPA
WPA2SummaryExam Preparation TasksReview All the Key TopicsComplete Tables and Lists from MemoryDefine Key TermsReview QuestionsChapter 9 Optimizing Network PerformanceFoundation TopicsHigh AvailabilityHigh-Availability MeasurementFault-Tolerant Network DesignHardware RedundancyLayer 3 RedundancyDesign Considerations for High-Availability NetworksHigh-Availability Best PracticesContent CachingLoad BalancingQoS TechnologiesIntroduction to QoSQoS Configuration StepsQoS ComponentsQoS MechanismsClassificationMarkingCongestion ManagementCongestion AvoidancePolicing and ShapingLink EfficiencyCase Study: SOHO Network DesignCase Study ScenarioSuggested SolutionIP AddressingLayer 1 MediaLayer 2 DevicesLayer 3 DevicesWireless DesignEnvironmental FactorsCost Savings Versus PerformanceTopologySummaryExam Preparation Tasks
Review All the Key TopicsComplete Tables and Lists from MemoryDefine Key TermsReview QuestionsChapter 10 Using Command-Line UtilitiesFoundation TopicsWindows CommandsarpipconfignbtstatnetstatnslookuppingroutetracertUNIX Commandsarpdig and nslookuphostifconfigtraceroutenetstatpingSummaryExam Preparation TasksReview All the Key TopicsComplete Tables and Lists from MemoryDefine Key TermsReview QuestionsChapter 11 Managing a NetworkFoundation TopicsMaintenance ToolsBit-Error Rate TesterButt SetCable CertifierCable TesterConnectivity SoftwareCrimperElectrostatic Discharge Wrist StrapEnvironmental MonitorLoopback PlugMultimeter
Protocol AnalyzerPunch-Down ToolThroughput TesterTime Domain Reflectometer/Optical Time Domain ReflectometerToner ProbeConfiguration ManagementMonitoring Resources and ReportsSNMPSyslogLogsApplication LogsSecurity LogsSystem LogsSummaryExam Preparation TasksReview All the Key TopicsComplete Tables and Lists from MemoryDefine Key TermsReview QuestionsChapter 12 Securing a NetworkFoundation TopicsSecurity FundamentalsNetwork Security GoalsConfidentialityIntegrityAvailabilityCategories of Network AttacksConfidentiality AttacksIntegrity AttacksAvailability AttacksDefending Against AttacksUser TrainingPatchingSecurity PoliciesGoverning PolicyTechnical PoliciesEnd User PoliciesMore Detailed DocumentsIncident ResponseVulnerability ScannersNessusNmap
Honey Pots and Honey NetsAccess Control ListsRemote Access SecurityFirewallsFirewall TypesFirewall Inspection TypesPacket-Filtering FirewallStateful FirewallFirewall ZonesVirtual Private NetworksOverview of IPsecIKE Modes and PhasesAuthentication Header and Encapsulating Security PayloadThe Five Steps in Setting Up and Tearing Down an IPsec Site-to-Site VPNOther VPN TechnologiesIntrusion Detection and PreventionIDS Versus IPSIDS and IPS Device CategoriesDetection MethodsDeploying Network-Based and Host-Based SolutionsSummaryExam Preparation TasksReview All the Key TopicsComplete Tables and Lists from MemoryDefine Key TermsReview QuestionsChapter 13 Troubleshooting Network IssuesFoundation TopicsTroubleshooting BasicsTroubleshooting FundamentalsStructured Troubleshooting MethodologyPhysical Layer TroubleshootingPhysical Layer Troubleshooting: ScenarioPhysical Layer Troubleshooting: SolutionData Link Layer TroubleshootingData Link Layer Troubleshooting: ScenarioData Link Layer Troubleshooting: SolutionNetwork Layer TroubleshootingLayer 3 Data StructuresCommon Layer 3 Troubleshooting IssuesNetwork Layer Troubleshooting: ScenarioNetwork Layer Troubleshooting: Solution
Wireless TroubleshootingWireless Network Troubleshooting: ScenarioWireless Network Troubleshooting: SolutionSummaryExam Preparation TasksReview All the Key TopicsComplete Tables and Lists from MemoryDefine Key TermsReview QuestionsChapter 14 Final PreparationTools for Final PreparationPearson Cert Practice Test Engine and Questions on the DVDInstall the Software from the DVDActivate and Download the Practice ExamActivating Other ExamsPremium EditionVideo Training on DVDMemory TablesEnd-of-Chapter Review ToolsSuggested Plan for Final Review and StudySummaryAPPENDIX A Answers to Review QuestionsAPPENDIX B CompTIA Network+ N10-005 Exam Updates, Version 1.0GlossaryIndexAPPENDIX C Memory Tables (DVD Only)APPENDIX D Memory Table Answer Key (DVD Only)Reader ServicesVisit our website and register this bookatwww.pearsonitcertification.com/title/9780789748218 for convenient accessto any updates, downloads, or errata that might be available for this book.CompTIA Network+The CompTIA Network+ (2011 Edition) certification ensures that thesuccessful candidate has the important knowledge and skills necessary tomanage, maintain, troubleshoot, install, operate, and configure basic networkinfrastructure, describe networking technologies, basic design principles, andadhere to wiring standards and use testing tools.It Pays to Get Certified
In a digital world, digital literacy is an essential survival skill—Certification proves you have the knowledge and skill to solve businessproblems in virtually any business environment. Certifications are highlyvalued credentials that qualify you for jobs, increased compensation, andpromotion.CompTIA Network+ certification held by many IT staff inorganizations—21% of IT staff within a random sampling of U.S.organizations within a cross section of industry verticals hold Network+certification.• The CompTIA Network+ credential—Proves knowledge of networkingfeatures and functions and is the leading vendor-neutral certification fornetworking professionals.• Starting Salary—The average starting salary of network engineers can beup to $70,000.• Career Pathway—CompTIA Network+ is the first step in starting anetworking career and is recognized by Microsoft as part of their MS program.Other corporations, such as Novell, Cisco, and HP, also recognize CompTIANetwork+ as part of their certification tracks.• More than 260,000—Individuals worldwide are CompTIA Network+certified.• Mandated/recommended by organizations worldwide—Such asCisco, HP, Ricoh, the U.S. State Department, and U.S. government contractorssuch as EDS, General Dynamics, and Northrop Grumman.How Certification Helps Your CareerCompTIA Career PathwayCompTIA offers a number of credentials that form a foundation for yourcareer in technology and allow you to pursue specific areas of concentration.Depending on the path you choose to take, CompTIA certifications help you
build upon your skills and knowledge, supporting learning throughout yourentire career.Join the Professional Community
Content Seal of QualityThis courseware bears the seal of CompTIA Approved QualityContent. This seal signifies this content covers 100% of the exam objectivesand implements important instructional design principles. CompTIArecommends multiple learning tools to help increase coverage of the learningobjectives.Why CompTIA?• Global Recognition—CompTIA is recognized globally as the leading ITnon-profit trade association and has enormous credibility. Plus, CompTIA’scertifications are vendor-neutral and offer proof of foundational knowledgethat translates across technologies.• Valued by Hiring Managers—Hiring managers value CompTIAcertification, because it is vendor- and technology-independent validation ofyour technical skills.• Recommended or Required by Government and Businesses—Manygovernment organizations and corporations either recommend or requiretechnical staff to be CompTIA certified. (For example, Dell, Sharp, Ricoh, theU.S. Department of Defense, and many more.)• Three CompTIA Certifications Ranked in the Top 10—In a study byDICE of 17,000 technology professionals, certifications helped commandhigher salaries at all experience levels.How to Obtain More Information
• Visit CompTIA online—www.comptia.org to learn more about gettingCompTIA certified.• Contact CompTIA—Call 866-835-8020 ext. 5 email@example.com.• Join the IT Pro community—http://itpro.comptia.org to join the ITcommunity to get relevant career information.• Connect with us—IntroductionThe CompTIA Network+ certification is a popular certification for thoseentering the computer-networking field. Although many vendor-specificnetworking certifications are popular in the industry, the CompTIA Network+certification is unique in that it is vendor-neutral. The CompTIA Network+certification often acts as a stepping-stone to more specialized and vendor-specific certifications, such as those offered by Cisco Systems.Notice in your CompTIA Network+ study that the topics are mostly generic, inthat they can apply to networking equipment regardless of vendor. However,as you grow in your career, I encourage you to seek specialized training for theequipment you work with on a daily basis.Goals and MethodsThe goal of this book is twofold. The #1 goal of this book is a simple one: tohelp you pass the N10-005 version of the CompTIA Network+ exam.To aid you in mastering and understanding the Network+ certificationobjectives, this book uses the following methods:• Opening topics list: This defines the topics that are covered in the chapter.• Foundation topics: At the heart of a chapter, this section explains thetopics from a hands-on and a theory-based standpoint. This includes in-depthdescriptions, tables, and figures that build your knowledge so that you canpass the N10-005 exam. The chapters are each broken into multiple sections.
• Key topics: This indicates important figures, tables, and lists of informationthat you need to know for the exam. They are sprinkled throughout eachchapter and are summarized in table format at the end of each chapter.• Memory tables: These can be found on the DVD within Appendices C andD. Use them to help memorize important information.• Key terms: Key terms without definitions are listed at the end of eachchapter. Write down the definition of each term, and check your work againstthe complete key terms in the Glossary.For current information about the CompTIA Network+ certification exam, youcanvisithttp://certification.comptia.org/getCertified/certifications/network.aspx.Who Should Read This Book?The CompTIA Network+ exam measures the necessary competencies for anentry-level networking professional with the equivalent knowledge of at least500 hours of hands-on experience in the lab or field. This book was written forpeople who have that amount of experience working with computer networks.Average readers will have connected a computer to a network, configured IPaddressing on that computer, installed software on that computer, usedcommand-line utilities (for example, the ping command), and used a browserto connect to the Internet.Readers will range from people who are attempting to attain a position in theIT field to people who want to keep their skills sharp or perhaps retain theirjob because of a company policy that mandates they take the new exams.This book also targets the reader who wants to acquire additionalcertifications beyond the Network+ certification (for example, the CiscoCertified Network Associate [CCNA] certification and beyond). The book isdesigned in such a way to offer easy transition to future certification studies.Strategies for Exam PreparationStrategies for exam preparation vary, depending on your existing skills,knowledge, and equipment available. Of course, the ideal exam preparationwould include building and configuring a computer network from scratch.Preferably, the network would contain both Microsoft Windows® and UNIXhosts, at least two Ethernet switches, and at least two routers.However, not everyone has access to this equipment, so the next best step youcan take is to read the chapters in this book, jotting down notes with keyconcepts or configurations on a separate notepad. For more visual learners,you might consider the Network+ Video Mentor product by Anthony Sequeira,which is available from Pearson IT Certification, where you get to watch anexpert perform multiple configurations.After you read the book, you can download the current exam objectives bysubmitting a form on the following web
page:http://certification.comptia.org/Training/testingcenters/examobjectives.aspxIf there are any areas shown in the certification exam outline that you stillwant to study, find those sections in this book and review them.When you feel confident in your skills, attempt the practice exam, which isincluded on this book’s DVD. As you work through the practice exam, note theareas where you lack confidence and review those concepts or configurationsin this book. After you review these areas, work through the practice exam asecond time, and rate your skills. Keep in mind that the more you workthrough the practice exam, the more familiar the questions become, and thepractice exam becomes a less accurate judge of your skills.After you work through the practice exam a second time and feel confidentwith your skills, schedule the real CompTIA Network+ exam (N10-005). Thefollowing website provides information about registering for theexam:http://certification.comptia.org/Training/testingcenters.aspxTo prevent the information from evaporating out of your mind, you shouldtypically take the exam within a week of when you consider yourself ready totake it.CompTIA Network+ Exam TopicsTable I-1 lists general exam topics (objectives) and specific topics under eachgeneral topic (subobjectives) for the CompTIA Network+ N10-005 exam. Thistable also lists the chapter in which each exam topic is covered. Note thatsome objectives and subobjectives are addressed in multiple chapters. Table I-1 CompTIA Network+ Exam Topics
How This Book Is OrganizedAlthough this book could be read cover-to-cover, it is designed to be flexibleand allow you to easily move between chapters and sections of chapters tocover just the material that you need more work with. However, if you dointend to read all the chapters, the order in the book is an excellent sequenceto use:• Chapter 1, ―Introducing Computer Networks,‖ introduces thepurpose of computer networks and their constituent components.Additionally, networks are categorized by their geography, topology, andresource location.• Chapter 2, ―Dissecting the OSI Model,‖ presents the two networkmodels: the OSI model and the TCP/IP stack. These models categorize variousnetwork components from a network cable up to and including an application,such as e-mail. These models are contrasted, and you are given a listing ofwell-known TCP and UDP port numbers used for specific applications.• Chapter 3, ―Identifying Network Components.‖ A variety of networkcomponents are introduced in this chapter. You are given an explanation ofvarious media types, the roles of specific infrastructure components, and the
features provided by specialized network devices (for example, a firewall orcontent switch).• Chapter 4, ―Understanding Ethernet.‖ The most widely deployed LANtechnology is Ethernet, and this chapter describes the characteristics ofEthernet networks. Topics include media access, collision domains, broadcastdomains, and distance/speed limitations for popular Ethernet standards.Additionally, you are introduced to some of the features available on Ethernetswitches, such as VLANs, trunks, STP, link aggregation, PoE, port monitoring,and user authentication.• Chapter 5, ―Working with IP Addresses.‖ One of the most challengingconcepts for many CompTIA Network+ students is IP subnetting. This chapterdemystifies IP subnetting by reviewing the basics of binary numbering, beforedelving into basic subnetting and then advanced subnetting. Although most ofthe focus of this chapter is on IP version 4 (IPv4) addressing, the chapterconcludes with an introduction to IP version 6 (IPv6).• Chapter 6, ―Routing Traffic.‖ A primary job of a computer network is toroute traffic between subnets. This chapter reviews the operation of routing IPtraffic and discusses how a router obtains routing information. One way arouter can populate its routing table is through the use of dynamic routingprotocols, several of which are discussed in this chapter. Many environments(such as a home network connecting to the Internet via a cable modem) useNAT to convert between private IP addresses inside a network and public IPaddresses outside a network. This chapter discusses DNAT, SNAT, and PAT.Although the primary focus on this chapter is on unicast routing, the chapterconcludes with a discussion of multicast routing.• Chapter 7, ―Introducing Wide-Area Networks.‖ Many corporatenetworks need to interconnect multiple sites separated by large distances.Connections between such geographically dispersed sites make up a WAN.This chapter discusses three categories of WAN connections and contrastsvarious WAN connection types, based on supported data rates and mediatypes. Finally, this chapter lists characteristics for multiple WAN technologies.• Chapter 8, ―Connecting Wirelessly.‖ In this increasingly mobile world,wireless technologies are exploding in popularity. This chapter discusses thebasic operation of WLANs. Additionally, WLAN design and securityconsiderations are addressed.• Chapter 9, ―Optimizing Network Performance.‖ This chapterexplains the importance of high availability for a network and whatmechanisms help provide a high level of availability. Network performanceoptimization strategies are addressed, including a section on QoS. Finally, thischapter allows you to use what you have learned in this and precedingchapters to design a SOHO network.
• Chapter 10, ―Using Command-Line Utilities.‖ In your dailyadministration and troubleshooting of computer networks, you needfamiliarity with various command-line utilities available on the operatingsystems present in your network. This chapter presents a collection of popularcommand-line utilities for both Microsoft Windows® and UNIX platforms.• Chapter 11, ―Managing a Network,‖ reviews some of the more commontools used to physically maintain a network. The components of configurationmanagement are also presented. Finally, this chapter discusses some of thenetwork-monitoring tools available to network administrators and what typesof information are included in various logs.• Chapter 12, ―Securing a Network.‖ Network security is an issue for mostany network, and this chapter covers a variety of network securitytechnologies. You begin by understanding the goals of network security andthe types of attacks you must defend against. Then, you review a collection ofsecurity best practices. Next, the chapter discusses specific securitytechnologies, including firewalls, VPNs, IDSs, and IPSs.• Chapter 13, ―Troubleshooting Network Issues.‖Troubleshootingnetwork issues in an inherent part of network administration, and this chapterpresents a structured approach to troubleshooting various networktechnologies. Specifically, you learn how to troubleshoot common Layer 2,Layer 3, and wireless network issues.• Chapter 14, ―Final Preparation,‖ reviews the exam-preparation toolsavailable in this book and the enclosed DVD. For example, the enclosed DVDcontains a practice exam engine and a collection of ten training videospresented by the author. Finally, a suggested study plan is presented to assistyou in preparing for the CompTIA Network+ exam (N10-005).In addition to the 13 main chapters, this book includes tools to help you verifythat you are prepared to take the exam. The DVD includes a practice test andmemory tables that you can work through to verify your knowledge of thesubject matter. The DVD also contains ten training videos that cover some ofthe most fundamental and misunderstood content in the CompTIA Network+curriculum, specifically the OSI model and IP addressing.Chapter 1. Introducing Computer NetworksAfter completion of this chapter, you will be able to answer the followingquestions:• What is the purpose of a network?• What are some examples of network components?• How are networks defined by geography?• How are networks defined by topology?• How are networks defined by resource location?
What comes to mind when you think of a computer network? Is it theInternet? Is it e-mail? Is it the wireless connection that lets you print to yourprinter from your laptop?Whatever your current perception of a computer network, this chapter andbook, as a whole, helps you gain deep appreciation and understanding ofnetworked computing. Be aware that although we commonly think ofcomputer networks as interconnecting computers, today, computer networksinterconnect a variety of devices in addition to just computers. Examplesinclude game consoles, video-surveillance devices, and IP-based telephones.Therefore, throughout this book, you can think of the term computernetwork as being synonymous with the more generic term network, as theseterms will be used interchangeably.In this chapter, the goal is to acquaint you with the purpose of a network andhelp you categorize a given network based on criteria such as geography,topology, and the location of a network’s resources. An implied goal of thisand all other chapters in this book is to prepare you to successfully pass theCompTIA Network+ exam, which is considered to be a cornerstone exam inthe information technology (IT) industry.Foundation Topics: Defining a NetworkIt was in the movie A Field of Dreams where they said, ―If you build it, theywill come.‖ That phrase most certainly applies to the evolution of network-based services seen in modern-day networks. Computer networks are nolonger relegated to allowing a group of computers to access a common set offiles stored on a computer designated as a file server. Instead, with thebuilding of high-speed, highly redundant networks, network architects areseeing the wisdom of placing a variety of traffic types on a single network.Examples include voice and video, in addition to data.One could argue that a network is the sum of its parts. So, as you begin yourstudy of networking, you should grasp a basic understanding of fundamentalnetworking components. These components include such entities as a client,server, hub, switch, router, and the media used to interconnect these devices.The Purpose of NetworksAt its essence, a network’s purpose is to make connections. These connectionsmight be between a PC and a printer or between a laptop and the Internet, asjust a couple of examples. However, the true value of a network comes fromthe traffic flowing over those connections. Consider a sampling of applicationsthat can travel over a network’s connections:• File sharing between two computers• Video chatting between computers located in different parts of the world
• Surfing the web (for example, to use social media sites, watch streamingvideo, listen to an Internet radio station, or do research for a school termpaper)• Instant messaging (IM) between computers with IM software installed• E-mail• Voice over IP (VoIP), to replace traditional telephony systemsA term commonly given to a network transporting multiple types of traffic (forexample, voice, video, and data) is a converged network. A converged networkmight offer significant cost savings to organizations that previously supportedseparate network infrastructures for voice, data, and video traffic. Thisconvergence can also potentially reduce staffing costs, because only a singlenetwork needs to be maintained, rather than separate networks for separatetraffic types.Overview of Network ComponentsDesigning, installing, administering, and troubleshooting a network requiresthe ability to recognize various network components and their functions.Although this is the focus of Chapter 3, ―Identifying Network Components,‖before we can proceed much further, we need a basic working knowledge ofhow individual components come together to form a functioning network.The components to consider for now are client, server, hub, switch, router,media, and wide-area network (WAN) link. As a reference for this discussion,consider Figure 1-1. Figure 1-1 Sample Computer NetworkThe following list describes the network components depicted in Figure 1-1 and the functions they serve:• Client: The term client defines the device an end user uses to access anetwork. This device might be a workstation, laptop, smartphone withwireless capabilities, or a variety of other end-user terminal devices.
• Server: A server, as the name suggests, serves up resources to a network.These resources might include e-mail access as provided by an e-mail server,web pages as provided by a web server, or files available on a file server.• Hub: A hub is an older technology that interconnects network components,such as clients and servers. Hubs vary in their number of available ports.However, for scalability, hubs can be interconnected, up to a point. If toomany hubs are chained together, network errors can result. As discussedfurther in Chapter 3, a hub does not perform any inspection of the traffic itpasses. Rather, a hub simply receives traffic in a port (that is, a receptacle towhich a network cable connects) and repeats that traffic out all of the otherports.• Switch: Like a hub, a switch interconnects network components, and theyare available with a variety of port densities. However, unlike a hub, a switchdoes not simply take traffic in on one port and blast that traffic out all otherports. Rather, a switch learns which devices reside off of which ports. As aresult, when traffic comes in a switch port, the switch interrogates the trafficto see where it is destined. Then, based on what the switch has learned, theswitch forwards the traffic out of the appropriate port, and not out all of theother ports. This dramatically cuts down on the volume of traffic coursingthrough your network. A switch is considered a Layer 2 device, which meansthat it makes its forwarding decisions based on addresses that are physicallyburned into a network interface card (NIC) installed in ahost (that is, anydevice that transmits or receives traffic on a network). This burned-in addressis a Media Access Control (MAC) address.• Router: As discussed in Chapter 3, a router is considered to be aLayer3 device, which means that it makes its forwarding decisions based on logicalnetwork addresses. Most modern networks useInternet Protocol (IP)addressing. Therefore, most routers know what logical IP networks reside offof which router interfaces. Then, when traffic comes into a router, the routerexamines the destination IP address of the traffic and, based on the router’sdatabase of networks (that is, the routing table), the router intelligentlyforwards the traffic out the appropriate interface.• Media: The previously mentioned devices need to be interconnected viasome sort of media. This media could be copper cabling. It could be a fiber-optic cable. Media might not even be a cable, as is the case with wirelessnetworks, where radio waves travel through the media of air.Chapter3 expands on this discussion of media. For now, realize that media varies in itscost, bandwidth capacity, and distance limitation. For example, althoughfiber-optic cabling is more expensive than unshielded twisted-pair cabling, itcan typically carry traffic over longer distances and has a greater bandwidthcapacity (that is, the capacity to carry a higher data rate).
• WAN link: Today, most networks connect to one or more other networks.For example, if your company has two locations, and those two locations areinterconnected (perhaps via a Frame Relay or Multiprotocol Label Switching[MPLS] network), the link that interconnects those networks is typicallyreferred to as a wide-area network (WAN) link. WANs, and technologiessupporting WANs, are covered in Chapter 7, ―Introducing Wide-AreaNetworks.‖Networks Defined by GeographyAs you might be sensing at this point, not all networks look the same. Theyvary in numerous ways. One criterion by which we can classify networks ishow geographically dispersed the networks components are. For example, anetwork might interconnect devices within an office, or a network mightinterconnect a database at a corporate headquarters location with a remotesales office located on the opposite side of the globe.Based on the geographical dispersion of network components, networks canbe classified into various categories, including the following:• Local-area network (LAN)• Wide-area network (WAN)• Campus-area network (CAN)• Metropolitan-area network (MAN)• Personal-area network (PAN)The following sections describe these different classifications of networks inmore detail.LANA LAN interconnects network components within a local region (for example,within a building). Examples of common LAN technologies you’re likely toencounter include Ethernet (that is, IEEE 802.3) and wireless networks (thatis, IEEE 802.11). Figure 1-2 illustrates an example of a LAN. Figure 1-2 Sample LAN Topology
NoteIEEE stands for the Institute of Electrical and Electronics Engineers, and it isan internationally recognized standards body.WANA WAN interconnects network components that are geographically separated.For example, a corporate headquarters might have multiple WAN connectionsto remote office sites. Multiprotocol Label Switching (MPLS), AsynchronousTransfer Mode (ATM), and Frame Relay are examples of WANtechnologies.Figure 1-3 depicts a simple WAN topology, which interconnectstwo geographically dispersed locations. Figure 1-3 Sample WAN TopologyOther Categories of NetworksAlthough LANs and WANs are the most common terms used to categorizecomputer networks based on geography, other categories include campus-areanetwork (CAN), metropolitan-area network (MAN), and personal-areanetwork (PAN).CAN
Years ago, I was a network manager for a university. The university coveredseveral square miles and had several dozen buildings. Within many of thesebuildings was a LAN. However, those building-centric LANs wereinterconnected. By interconnecting these LANs, another network type wascreated, a CAN. Besides an actual university campus, a CAN might also befound in an industrial park or business park.MANMore widespread than a CAN and less widespread than a WAN, a MANinterconnects locations scattered throughout a metropolitan area. Imagine, forexample, that a business in Chicago had a location near O’Hare Airport,another location near the Navy Pier, and another location in the Sears Tower.If a service provider could interconnect those locations using a high-speednetwork, such as a 10-Gbps (that is, 10 billion bits per second) network, theinterconnection of those locations would constitute a MAN. One example of aMAN technology is Metro Ethernet.PANA PAN is a network whose scale is even smaller than a LAN. As an example, aconnection between a PC and a digital camera via a universal serial bus (USB)cable could be considered a PAN. Another example is a PC connected to anexternal hard drive via a FireWire connection. A PAN, however, is notnecessarily a wired connection. A Bluetooth connection between your cellphone and your car’s audio system is considered a wireless PAN (WPAN). Themain distinction of a PAN, however, is that its range is typically limited to justa few meters.Networks Defined by TopologyIn addition to classifying networks based on the geographical placement oftheir components, another approach to classifying a network is to use thenetwork’s topology. Looks can be deceiving, however. You need to be able todistinguish between a physical topology and a logical topology.Physical Versus Logical TopologyJust because a network appears to be a star topology (that is, where thenetwork components all connect back to a centralized device, such as aswitch), the traffic might be flowing in a circular pattern through all thenetwork components attached to the centralized device. The actual traffic flowdetermines the logical topology, while how components are physicallyinterconnected determines thephysical topology.As an example, consider Figure 1-4. The figure shows a collection of computersconnected to a Token Ring Media Access Unit (MAU). From a quickinspection ofFigure 1-4, you can conclude that the devices are physically
connected in a star topology, where the connected devices radiate out from acentralized aggregation point (that is, the MAU in this example). Figure 1-4 Physical Star TopologyNext, contrast the physical topology in Figure 1-4 with the logical topologyillustrated in Figure 1-5. Although the computers physically connect to acentralized MAU, when you examine the flow of traffic through (or in thiscase, around) the network, you see that the traffic flow actually loops round-and-round the network. The traffic flow dictates how to classify a network’slogical topology. In this instance, the logical topology is a ring topology,because the traffic circulates around the network as if circulating around aring. Figure 1-5 Logical Ring Topology
Although Token Ring, as used in this example, is rarely seen in modernnetworks, it illustrates how a network’s physical and logical topologies can bequite different.Bus TopologyA bus topology, as depicted in Figure 1-6, typically uses a cable runningthrough the area requiring connectivity. Devices that need to connect to thenetwork then tap into this nearby cable. Early Ethernet networks commonlyrelied on bus topologies. Figure 1-6 Bus TopologyA network tap might be in the form of a T connector (commonly used in older10BASE2 networks) or a vampire tap (commonly used in older 10BASE5networks). Figure 1-7 shows an example of a T connector. Figure 1-7 T Connector
NoteThe Ethernet standards mentioned here (that is, 10BASE2 and 10BASE5), inaddition to many other Ethernet standards, are discussed in detail in Chapter4, ―Understanding Ethernet.‖A bus and all devices connected to that bus make up a network segment. Asdiscussed in Chapter 4, a single network segment is a single collision domain,which means that all devices connected to the bus might try to gain access tothe bus at the same time, resulting in an error condition known asa collision. Table 1-1 identifies some of the primary characteristics, benefits,and drawbacks of a bus topology. Table 1-1 Characteristics, Benefits, and Drawbacks of a Bus Topology
Ring TopologyFigure 1-8 offers an example of a ring topology, where traffic flows in a circularfashion around a closed network loop (that is, a ring). Typically, a ringtopology sends data, in a single direction, to each connected device in turn,until the intended destination receives the data. Token Ring networks typicallyrelied on a ring topology, although the ring might have been the logicaltopology, while physically, the topology was a star topology. Figure 1-8 Ring Topology
Token Ring, however, was not the only popular ring-based topology popular innetworks back in the 1990s. Fiber Distributed Data Interface (FDDI) wasanother variant of a ring-based topology. Most FDDI networks (which, as thename suggests, have fiber optics as the media) used not just one ring, but two.These two rings sent data in opposite directions, resulting in counter-rotatingrings. One benefit of counter-rotating rings was that if a fiber broke, thestations on each side of the break could interconnect their two rings, resultingin a single ring capable of reaching all stations on the ring.Because a ring topology allows devices on the ring to take turns transmittingon the ring, contention for media access was not a problem, as it was for a bustopology. If a network had a single ring, however, the ring became a singlepoint of failure. If the ring were broken at any point, data would stopflowing. Table 1-2identifies some of the primary characteristics, benefits, anddrawbacks of a ring topology. Table 1-2 Characteristics, Benefits, and Drawbacks of a Ring Topology
Star TopologyFigure 1-9 shows a sample star topology with a hub at the center of thetopology and a collection of clients individually connected to the hub. Noticethat a star topology has a central point from which all attached devices radiate.In LANs, that centralized device was typically a hub back in the early 1990s.Modern networks, however, usually have a switch located at the center of thestar. Figure 1-9 Star Topology
NoteChapter 3 discusses UTP and other types of cabling.The star topology is the most popular physical LAN topology in use today, withan Ethernet switch at the center of the star and unshielded twisted-pair cable(UTP) used to connect from the switch ports to clients.Table 1-3 identifies some of the primary characteristics, benefits, anddrawbacks of a star topology. Table 1-3 Characteristics, Benefits, and Drawbacks of a Star TopologyHub-and-Spoke TopologyWhen interconnecting multiple sites (for example, multiple corporatelocations) via WAN links, a hub-and-spoke topology has a WAN link from eachremote site (that is, a spoke site) to the main site (that is, the hub site). Thisapproach, an example of which is shown in Figure 1-10, is similar to the startopology used in LANs. Figure 1-10 Hub-and-Spoke Topology
With WAN links, a service provider is paid a recurring fee for each link.Therefore, a hub-and-spoke topology helps minimize WAN expenses by notdirectly connecting any two spoke locations. If two spoke locations need tocommunicate between themselves, their communication is sent via the hublocation. Table 1-4 contrasts the benefits and drawbacks of a hub-and-spokeWAN topology. Table 1-4 Characteristics, Benefits, and Drawbacks of a Hub-and-Spoke WAN Topology
Full-Mesh TopologyAlthough a hub-and-spoke WAN topology lacked redundancy and sufferedfrom suboptimal routes, a full-mesh topology, as shown in Figure 1-11, directlyconnects every site to every other site. Figure 1-11 Full-Mesh TopologyBecause each site connects directly to every other site, an optimal path can beselected, as opposed to relaying traffic via another site. Also, a full-meshtopology is highly fault tolerant. By inspecting Figure 1-11, you can see thatmultiple links in the topology could be lost, and every site might still be able toconnect to every other site. Table 1-5 summarizes the characteristics of a full-mesh topology. Table 1-5 Characteristics, Benefits, and Drawbacks of a Full-Mesh WAN Topology
Partial-Mesh TopologyA partial-mesh WAN topology, as depicted in Figure 1-12, is a hybrid of thepreviously described hub-and-spoke topology and full-mesh topology.Specifically, a partial-mesh topology can be designed to provide an optimalroute between selected sites, while avoiding the expense of interconnectingevery site to every other site. Figure 1-12 Partial-Mesh Topology
When designing a partial-mesh topology, a network designer must considernetwork traffic patterns and strategically add links interconnecting sites thathave higher volumes of traffic between themselves. Table 1-6 highlights thecharacteristics, benefits, and drawbacks of a partial-mesh topology. Table 1-6 Characteristics, Benefits, and Drawbacks of a Partial-Mesh TopologyNetworks Defined by Resource LocationYet another way to categorize networks is based on where network resourcesreside. An example of a client-server network is a collection of PCs all sharingfiles located on a centralized server. However, if those PCs had their operatingsystem (OS) (for example, Microsoft Windows 7 or Mac OS X) configured for
file sharing, they could share files from one another’s hard drives. Such anarrangement would be referred to as a peer-to-peer network, because thepeers (that is, the PCs in this example) make resources available to otherpeers. The following sections describe client-server and peer-to-peer networksin more detail.Client-Server NetworksFigure 1-13 illustrates an example of a client-server network, where adedicated file server provides shared access to files, and a networked printer isavailable as a resource to the network’s clients. Client-server networks arecommonly used by businesses. Because resources are located on one or moreservers, administration is simpler than trying to administer network resourceson multiple peer devices. Figure 1-13 Client-Server Network ExamplePerformance of a client-server network can be better than that of a peer-to-peer network, because resources can be located on dedicated servers, ratherthan on a PC running a variety of end-user applications. Backups can besimplified, since fewer locations must be backed up. However, client-servernetworks come with the extra expense of dedicated server resources. Table 1-7 contrasts the benefits and drawbacks of client-server networks. Table 1-7 Characteristics, Benefits, and Drawbacks of a Client-Server Network
NoteA server in a client-server network could be a computer running anetworkoperating system (NOS), such as Novell NetWare or a variety of MicrosoftWindows Server OSs. Alternately, a server might be a host making its filesystem available to remote clients via the Network File System (NFS) service,which was originally developed by Sun Microsystems.NoteA variant of the traditional server in a client-server network, where the serverprovides shared file access, is network-attached storage (NAS). A NAS deviceis a mass storage device that attaches directly to a network. Rather thanrunning an advanced NOS, a NAS device typically makes files available tonetwork clients via a service such as NFS.Peer-to-Peer NetworksPeer-to-peer networks allow interconnected devices (for example, PCs) toshare their resources with one another. Those resources could be, for example,files or printers. As an example of a peer-to-peer network, consider Figure 1-14, where each of the peers can share files on their own hard drives, and one ofthe peers has a directly attached printer that can be shared with the otherpeers in the network. Figure 1-14 Peer-to-Peer Network Example
Peer-to-peer networks are commonly seen in smaller businesses and inhomes. The popularity of these peer-to-peer networks is fueled in part byclient operating systems which support file and print sharing. Scalability forpeer-to-peer networks is a concern, however. Specifically, as the number ofdevices (that is, peers) increases, the administration burden increases. Forexample, a network administrator might have to manage file permissions onmultiple devices, as opposed to a single server. Consider the characteristics ofpeer-to-peer networks as presented in Table 1-8. Table 1-8 Characteristics, Benefits, and Drawbacks of a Peer-to-Peer Network
NoteSome networks have characteristics of both peer-to-peer and client-servernetworks. For example, PCs in a company might all point to a centralizedserver for accessing a shared database in a client-server topology. However,these PCs might simultaneously share files and printers between one anotherin a peer-to-peer topology. Such a network, which has a mixture of client-server and peer-to-peer characteristics, is called a hybrid network.SummaryThe main topics covered in this chapter are the following:• You were introduced to various network components, including client,server, hub, switch, router, media, and WAN link.• One way to classify networks is by their geographical dispersion. Specifically,these network types were identified: LAN, WAN, CAN, MAN, and PAN.• Another approach to classifying networks is based on a network’s topology.Examples of network types, based on topology, include bus, ring, star, partialmesh, full mesh, and hub-and-spoke.• This chapter contrasted client-server and peer-to-peer networks.Exam Preparation TasksReview All the Key TopicsReview the most important topics from inside the chapter, noted with the KeyTopic icon in the outer margin of the page. Table 1-9 lists these key topics andthe page numbers where each is found. Table 1-9 Key Topics for Chapter 1
Complete Tables and Lists from MemoryPrint a copy of Appendix C, ―Memory Tables‖ (found on the DVD), or at leastthe section for this chapter, and complete as much of the tables as possiblefrom memory. Appendix D, ―Memory Tables Answer Key,‖ also on the DVD,includes the completed tables and lists so you can check your work.Define Key TermsDefine the following key terms from this chapter, and check your answers inthe Glossary:client,server,hub,switch,router,media,WAN link,local-area network (LAN),wide-area network (WAN),campus-area network (CAN),metropolitan-area network (MAN),personal-area network (PAN),logical topology,physical topology,bus topology,ring topology,star topology,hub-and-spoke topology,full-mesh topology,partial-mesh topology,client-server network,peer-to-peer networkReview QuestionsThe answers to these review questions appear in Appendix A, ―Answers toReview Questions.‖1. Which of the following is a device directly used by an end user to access anetwork?a. Serverb. LANc. Clientd. Router2. Which device makes traffic-forwarding decisions based on MAC addresses?a. Hub
b. Routerc. Switchd. Multiplexer3. A company has various locations in a city interconnected using MetroEthernet connections. This is an example of what type of network?a. WANb. CANc. PANd. MAN4. A network formed by interconnecting a PC to a digital camera via a USBcable is considered what type of network?a. WANb. CANc. PANd. MAN5. Which of the following LAN topologies requires the most cabling?a. Busb. Ringc. Stard. WLAN6. Which of the following topologies offers the highest level of redundancy?a. Full meshb. Hub and spokec. Busd. Partial mesh7. How many WAN links are required to create a full mesh of connectionsbetween five remote sites?a. 5b. 10c. 15d. 208. Identify two advantages of a hub-and-spoke WAN topology as compared toa full-mesh WAN topology. (Choose two.)a. Lower costb. Optimal routesc. More scalabled. More redundancy9. Which type of network is based on network clients sharing resources withone another?a. Client-serverb. Client-peerc. Peer-to-peer
d. Peer-to-server10. Which of the following is an advantage of a peer-to-peer network, ascompared with a client-server network?a. More scalableb. Less expensivec. Better performanced. Simplified administrationChapter 2. Dissecting the OSI ModelAfter completion of this chapter, you will be able to answer the followingquestions:• What is the purpose of a network model?• What are the layers of the OSI model?• What are the characteristics of each layer of the OSI model?• How does the TCP/IP stack compare to the OSI model?• What are the well-known TCP and/or UDP port numbers for a givencollection of common applications?Way back in 1977, the International Organization for Standardization (ISO)developed a subcommittee to focus on the interoperability of multivendorcommunications systems. What sprang from this subcommittee was the OpenSystems Interconnection (OSI) reference model (commonly referred to asthe OSI model or the OSI stack). With this model, you can take just about anynetworking technology and categorize that technology as residing at one ormore of the seven layers of the model.This chapter defines those seven layers and provides examples of what youmight find at each layer. Finally, this chapter contrasts the OSI model withanother model (the TCP/IP stack, also known as the Department ofDefense [DoD]model), which focuses on Internet Protocol (IP)communications.Foundation Topics: The Purpose of Reference ModelsThroughout your networking career, and throughout this book, you willencounter various protocols and devices that play a role in your network. Tobetter understand how a particular technology fits in, however, it helps to havea common point of reference against which various technologies from variousvendors can be compared.One of the most common ways of categorizing the function of a networktechnology is to state at what layer (or layers) of the OSI model thattechnology operates. Based on how that technology performs a certainfunction at a certain layer of the OSI model, you can better determine if onedevice is going to be able to communicate with another device, which might or
might not be using a similar technology at that layer of the OSI referencemodel.For example, when your laptop connects to a web server on the Internet, yourlaptop has been assigned an IP address. Similarly, the web server to which youare communicating has an IP address. As you see in this chapter, an IPaddress lives at Layer 3 (the network layer) of the OSI model. Because bothyour laptop and the web server use a common protocol (that is, IP) at Layer 3,they can communicate with one another.Personally, I’ve been in the computer-networking industry since 1989, and Ihave had the OSI model explained in many classes I’ve attended and booksI’ve read. From this, I’ve taken away a collection of metaphors to help describethe operation of the different layers of the OSI model. Some of the metaphorsinvolve sending a letter from one location to another or placing a message in aseries of envelopes. However, my favorite (and the most accurate) way todescribe the OSI model is to simply think of it as being analogous to abookshelf, such as the one shown in Figure 2-1. Figure 2-1 A Bookshelf Is Analogous to the OSI ModelIf you were to look at a bookshelf in my home, you’d see that I organizeddifferent types of books on different shelves. One shelf contains my collectionof Star Wars books, another shelf contains the books I wrote for Cisco Press,another shelf contains my audio books, and so on. I grouped similar bookstogether on a shelf, just as the OSI model groups similar protocols andfunctions together in a layer.
A common pitfall my students and readers encounter when studying the OSImodel is to try to neatly fit all the devices and protocols in their network intoone of the OSI model’s seven layers. However, not every technology is aperfect fit into these layers. In fact, some networks might not have anytechnologies operating at one or more of these layers. This reminds me of myfavorite statement regarding the OSI model. It comes from Rich Seifert’sbook The Switch Book. In that book, Rich reminds us that the OSI model isa reference model, not a reverence model. That is, there is no cosmic lawstating that all technologies must cleanly plug into the model. So, as youdiscover the characteristics of the OSI model layers throughout this chapter,remember that these layers are like shelves for organizing similar protocolsand functions, not immutable laws.The OSI ModelAs previously stated, the OSI model is comprised of seven layers:• Layer 1: The physical layer• Layer 2: The data link layer• Layer 3: The network layer• Layer 4: The transport layer• Layer 5: The session layer• Layer 6: The presentation layer• Layer 7: The application layerGraphically, these layers are usually depicted with Layer 1 at the bottom of thestack, as shown in Figure 2-2. Figure 2-2 OSI ―Stack‖Various mnemonics are available to help memorize these layers in theirproper order. A top-down (that is, starting at the top of the stack with Layer 7and working your way down to Layer 1) acrostic is All People Seem To NeedData Processing. As a couple of examples, using this acrostic, the A in All
reminds us of the A in Application, and the P in People reminds us ofthe P in Presentation.At the physical layer, binary expressions (that is, a series of 1s and 0s)represent data. A binary expression is made up of bits, where a bit is a single 1or a single 0. At upper layers, however, bits are grouped together, into what isknown as aprotocol data unit (PDU) or a data service unit.The term packet is used fairly generically to refer to these PDUs. However,PDUs might have an additional name, depending on their OSI layer. Figure 2-3illustrates these PDU names. A common memory aid for these PDUs is theacrostic Some People Fear Birthdays, where the S in Some reminds us ofthe S inSegments. The P in People reminds us of the P in Packets, andthe F in Fear reflects the F in Frames. Finally, the B in Birthdays reminds us ofthe B in Bits. Figure 2-3 PDU NamesLayer 1: The Physical LayerThe physical layer, as shown in Figure 2-4, is concerned with the transmissionof data on the network. Figure 2-4 Layer 1: The Physical Layer
As a few examples, the physical layer defines• How bits are represented on the medium: Data on a computernetwork is represented as a binary expression. Chapter 5, ―Working with IPAddresses,‖ discusses binary in much more detail. Electrical voltage (oncopper wiring) or light (carried via fiber-optic cabling) can represent these 1sand 0s.For example, the presence or the absence of voltage on a wire can represent abinary 1 or a binary 0, respectively, as illustrated in Figure 2-5. Similarly, thepresence or absence of light on a fiber-optic cable can represent a 1 or 0 inbinary. This type of approach is called current state modulation. Figure 2-5 Current State ModulationAn alternate approach to representing binary data is state transitionmodulation, as shown in Figure 2-6, where the transition between voltages orthe presence of light indicates a binary value. Figure 2-6 Transition Modulation
NoteOther modulation types you might be familiar with from radio includeamplitude modulation (AM) and frequency modulation (FM). AM uses avariation in a waveform’s amplitude (that is, signal strength) to represent theoriginal signal. However, FM uses a variation in frequency to represent theoriginal signal.• Wiring standards for connectors and jacks: Several standards fornetwork connectors are addressed in Chapter 3, ―Identifying NetworkComponents.‖ As an example, however, the TIA/EIA-568-B standarddescribes how an RJ-45 connector should be wired for use on a 100BASE-TXEthernet network, as shown in Figure 2-7. Figure 2-7 TIA/EIA-568-B Wiring Standard for an RJ-45 Connector• Physical topology: Layer 1 devices view a network as a physical topology(as opposed to a logical topology). Examples of a physical topology includebus, ring, and star topologies, as described in Chapter 1, ―IntroducingComputer Networks.‖• Synchronizing bits: For two networked devices to successfullycommunicate at the physical layer, they must agree on when one bit stops andanother bit starts. Specifically, what is needed is a method to synchronize thebits. Two basic approaches to bit synchronizationinclude asynchronous and synchronous synchronization:• Asynchronous: With this approach, a sender indicates that it’s about tostart transmitting by sending a start bit to the receiver. When the receiver sees
this, it starts its own internal clock to measure the subsequent bits. After thesender transmits its data, it sends a stop bit to indicate that is has finished itstransmission.• Synchronous: This approach synchronizes the internal clocks of both thesender and receiver to ensure that they agree on when bits begin and end. Acommon approach to make this synchronization happen is to use an externalclock (for example, a clock provided by a service provider), which is referencedby both the sender and receiver.• Bandwidth usage: The two fundamental approaches to bandwidth usageon a network are broadband and baseband:• Broadband: Broadband technologies divide the bandwidth available on amedium (for example, copper or fiber-optic cabling) into different channels.Different communication streams are then transmitted over the variouschannels. As an example, considerFrequency-Division Multiplexing (FDM)used by a cable modem. Specifically, a cable modem uses certain ranges offrequencies on the cable coming into your home from the local cable companyto carry incoming data, another range of frequencies for outgoing data, andseveral other frequency ranges for various TV stations.• Baseband: Baseband technologies, in contrast, use all the availablefrequencies on a medium to transmit data. Ethernet is an example of anetworking technology that uses baseband.• Multiplexing strategy: Multiplexing allows multiple communicationssessions to share the same physical medium. Cable TV, as previouslymentioned, allows you to receive multiple channels over a single physicalmedium (for example, a coaxial cable plugged into the back of your television).Here are some of the more common approaches to multiplexing:• Time-division multiplexing (TDM): TDM supports differentcommunication sessions (for example, different telephone conversations in atelephony network) on the same physical medium by causing the sessions totake turns. For a brief period of time, defined as a time slotdata from the firstsession will be sent, followed by data from the second session. This continuesuntil all sessions have had a turn, and the process repeats itself.• Statistical time-division multiplexing (StatTDM): A downside toTDM is that each communication session receives its own time slot, even ifone of the sessions does not have any data to transmit at the moment. Tomake a more efficient use of available bandwidth, StatTDM dynamicallyassigns time slots to communications sessions on an as-needed basis.• Frequency-division multiplexing (FDM): FDM divides a medium’sfrequency range into channels, and different communication sessions transmittheir data over different channels. As previously described, this approach tobandwidth usage is called broadband.
Examples of devices defined by physical layer standards include hubs, wirelessaccess points, and network cabling.NoteA hub can interconnect PCs in a LAN. However, it is considered to be aphysical layer device, because a hub takes bits coming in on one port andretransmits those bits out all other hub ports. At no point does the hubinterrogate any addressing information in the data.Layer 2: The Data Link LayerThe data link layer, as shown in Figure 2-8, is concerned with packaging datainto frames and transmitting those frames on the network, performing errordetection/correction, uniquely identifying network devices with an address,and handling flow control. These processes are collectively referred to as datalink control (DLC). Figure 2-8 Layer 2: The Data Link LayerIn fact, the data link layer is unique from the other layers in that it has twosublayers of its own: MAC and LLC.Media Access ControlCharacteristics of the Media Access Control (MAC) sublayer include thefollowing:• Physical addressing: A common example of a Layer 2 address is a MACaddress, which is a 48-bit address assigned to a device’s network interfacecard (NIC). The address is commonly written in hexadecimal notation (forexample, 58:55:ca:eb:27:83). The first 24 bits of the 48-bit address arecollectively referred to as the vendor code. Vendors of networking equipmentare assigned one or more unique vendor codes. You can use the list of vendor
codes athttp://standards.ieee.org/develop/regauth/oui/oui.txt to determine themanufacturer of a networking device, based on the first half of the device’sMAC address. Because each vendor is responsible for using unique values inthe last 24 bits of a MAC address, and because each vendor has a uniquevendor code, no two MAC addresses in the world should have the same value.• Logical topology: Layer 2 devices view a network as a logical topology.Examples of a logical topology include bus and ring topologies, as describedin Chapter 1.• Method of transmitting on the media: With several devices connectedto a network, there needs to be some strategy for determining when a device isallowed to transmit on the media. Otherwise, multiple devices might transmitat the same time, and interfere with one another’s transmissions.Logical Link ControlCharacteristics of the Logical Link Control (LLC) sublayer include thefollowing:• Connection services: When a device on a network receives a messagefrom another device on the network, that recipient device can providefeedback to the sender in the form of an acknowledgment message. The twomain functions provided by these acknowledgment messages are as follows:• Flow control: Limits the amount of data a sender can send at one time; thisprevents the receiver from being overwhelmed with too much information.• Error control: Allows the recipient of data to let the sender know if theexpected data frame was not received or if it was received, but is corrupted.The recipient determines if the data frame is corrupted by mathematicallycalculating a checksum of the data received. If the calculated checksum doesnot match the checksum received with the data frame, the recipient of the datadraws the conclusion that the data frame is corrupted and can then notify thesender via an acknowledgment message.• Synchronizing transmissions: Senders and receivers of data framesneed to coordinate when a data frame is being transmitted and should bereceived. Three methods of performing this synchronization are as follows:• Isochronous: With isochronous transmission, network devices look to acommon device in the network as a clock source, which creates fixed-lengthtime slots. Network devices can determine how much free space, if any, isavailable within a time slot and insert data into an available time slot. A timeslot can accommodate more than one data frame. Isochronous transmissiondoes not need to provide clocking at the beginning of a data string (as doessynchronous transmission) or for every data frame (as does asynchronoustransmission). As a result, isochronous transmission uses little overhead whencompared to asynchronous or synchronous transmission methods.
• Asynchronous: With asynchronous transmission, network devicesreference their own internal clocks, and network devices do not need tosynchronize their clocks. Instead, the sender places a start bit at the beginningof each data frame and a stop bit at the end of each data frame. These startand stop bits tell the receiver when to monitor the medium for the presence ofbits.An additional bit, called the parity bit, might also be added to the end of eachbyte in a frame to detect an error in the frame. For example, if even parityerror detection (as opposed to odd parity error detection) is used, the paritybit (with a value of either 0 or 1) would be added to the end of a byte, causingthe total number of 1s in the data frame to be an even number. If the receiverof a byte is configured for even parity error detection and receives a bytewhere the total number of bits (including the parity bit) is even, the receivercan conclude that the byte was not corrupted during transmission.NoteUsing a parity bit to detect errors might not be effective if a byte has morethan one error (that is, more than one bit that has been changed from itsoriginal value).• Synchronous: With synchronous transmission, two network devices thatwant to communicate between themselves must agree on a clocking method toindicate the beginning and ending of data frames. One approach to providingthis clocking is to use a separate communications channel over which a clocksignal is sent. Another approach relies on specific bit combinations or controlcharacters to indicate the beginning of a frame or a byte of data.Like asynchronous transmissions, synchronous transmissions can performerror detection. However, rather than using parity bits, synchronouscommunication runs a mathematical algorithm on the data to create a cyclicredundancy check (CRC). If both the sender and receiver calculate the sameCRC value for the same chunk of data, the receiver can conclude that the datawas not corrupted during transmission.Examples of devices defined by data link layer standards include switches,bridges, and network interface cards (NIC).NoteNICs are not entirely defined at the data link layer, because they are partiallybased on physical layer standards, such as a NIC’s network connector.Layer 3: The Network LayerThe network layer, as shown in Figure 2-9, is primarily concerned withforwarding data based on logical addresses.
Figure 2-9 Layer 3: The Network LayerAlthough many network administrators immediately think of routing and IPaddressing when they hear about the network layer, this layer is actuallyresponsible for a variety of tasks:• Logical addressing: Although the data link layer uses physical addressesto make forwarding decisions, the network layer uses logical addressing tomake forwarding decisions. A variety of routed protocols (for example,AppleTalk and IPX) have their own logical addressing schemes, but by far, themost widely deployed routed protocol is Internet Protocol (IP). IP addressingis discussed in detail in Chapter 5, ―Working with IP Addresses.‖• Switching: The term switching is often associated with Layer 2technologies; however, the concept of switching also exists at Layer 3.Switching, at its essence, is making decisions about how data should beforwarded. At Layer 3, three common switching techniques exist:• Packet switching: With packet switching, a data stream is divided intopackets. Each packet has a Layer 3 header, which includes a source anddestination Layer 3 address. Another term for packet switching is routing,which is discussed in more detail in Chapter 6, ―Routing Traffic.‖• Circuit switching: Circuit switching dynamically brings up a dedicatedcommunication link between two parties in order for those parties tocommunicate.As a simple example of circuit switching, think of making a phone call fromyour home to a business. Assuming you have a traditional landline servicingyour phone, the telephone company’s switching equipment interconnects yourhome phone with the phone system of the business you’re calling. Thisinterconnection (that is, circuit) only exists for the duration of the phone call.• Message switching: Unlike packet switching and circuit switchingtechnologies, message switching is usually not well-suited for real-timeapplications, because of the delay involved. Specifically, with message
switching, a data stream is divided into messages. Each message is tagged witha destination address, and the messages travel from one network device toanother network device on the way to their destination. Because these devicesmight briefly store the messages before forwarding them, a network usingmessage switching is sometimes called a store-and-forward network.Metaphorically, you could visualize message switching like routing an e-mailmessage, where the e-mail message might be briefly stored on an e-mail serverbefore being forwarded to the recipient.• Route discovery and selection: Because Layer 3 devices makeforwarding decisions based on logical network addresses, a Layer 3 devicemight need to know how to reach various network addresses. For example, acommon Layer 3 device is a router. A router can maintain a routing tableindicating how to forward a packet based on the packet’s destination networkaddress.A router can have its routing table populated via manual configuration (that is,by entering static routes), via a dynamic routing protocol (for example, RIP,OSPF, or EIGRP), or simply by the fact that the router is directly connected tocertain networks.NoteRouting protocols are discussed in Chapter 6.• Connection services: Just as the data link layer provided connectionservices for flow control and error control, connection services also exist at thenetwork layer. Connection services at the network layer can improve thecommunication reliability, in the event that the data link’s LLC sublayer is notperforming connection services.The following functions are performed by connection services at the networklayer:• Flow control (also known as congestion control): Helps prevent asender from sending data more rapidly that the receiver is capable is receivingthe data.• Packet reordering: Allows packets to be placed in the appropriatesequence as they are sent to the receiver. This might be necessary, becausesome networks support load-balancing, where multiple links are used to sendpackets between two devices. Because multiple links are used, packets mightarrive out of order.Examples of devices found at the network layer include routers and multilayerswitches. The most common Layer 3 protocol in use today, and the protocol onwhich the Internet is based, is IP.A less popular Layer 3 protocol is Novell’s Internetwork PacketExchange (IPX), which has its own format for Layer 3 addressing. Although
IPX is a Novell-developed protocol, most modern Novell networks use IP astheir Layer 3 protocol.NoteRouters and multilayer switches are discussed in Chapter 3.Layer 4: The Transport LayerThe transport layer, as shown in Figure 2-10, acts as a dividing line betweenthe upper layers and lower layers of the OSI model. Specifically, messages aretaken from upper layers (Layers 5–7) and are encapsulated into segments fortransmission to the lower layers (Layers 1–3). Similarly, data streams comingfrom lower layers are decapsulated and sent to Layer 5 (the session layer), orsome other upper layer, depending on the protocol. Figure 2-10 Layer 4: The Transport LayerTwo common transport layer protocols include Transmission ControlProtocol(TCP) and User Datagram Protocol (UDP):• Transmission Control Protocol (TCP): A connection-oriented transportprotocol. Connection-oriented transport protocols provide reliable transport,in that if a segment is dropped, the sender can detect that drop and retransmitthat dropped segment. Specifically, a receiver acknowledges segments that itreceives. Based on those acknowledgments, a sender can determine whichsegments were successfully received and which segments need to betransmitted again.• User Datagram Protocol (UDP): A connectionless transport protocol.Connectionless transport protocols provide unreliable transport, in that if asegment is dropped, the sender is unaware of the drop, and no retransmissionoccurs.A less popular Layer 4 protocol is Novell’s Sequenced Packet Exchange (SPX).Similar to the TCP/IP stack of protocols, Novell’s solution (much more
popular in the mid 1990s) was the IPX/SPX stack of protocols. However, mostmodern Novell networks rely on TCP/IP rather than IPX/SPX.NoteMicrosoft introduced its own implementation of Novell’s IPX/SPX, which wasnamed NWLink IPX/SPX.Just as Layer 2 and Layer 3 each offer flow control services, flow controlservices also exist at Layer 4. Two common flow control approaches at Layer 4are as follows:• Windowing: TCP communication uses windowing, in that one or moresegments are sent at one time, and a receiver can acknowledge the receipt ofall the segments in a window with a single acknowledgment. In some cases, asillustrated in Figure 2-11, TCP uses a sliding window, where the window sizebegins with one segment. If there is a successful acknowledgment of that onesegment (that is, the receiver sends an acknowledgment asking for the nextsegment), the window size doubles to two segments. Upon successful receiptof those two segments, the next window contains four segments. Thisexponential increase in window size continues until the receiver does notacknowledge successful receipt of all segments within a certain time period(known as the round trip time [RTT], which is sometimes called real transfertime), or until a configured maximum window size is reached. Figure 2-11 TCP Sliding Window
• Buffering: With buffering, a device (for example, a router) allocates achunk of memory (sometimes called a buffer or a queue) to store segments ifbandwidth is not currently available to transmit those segments. A queue hasa finite capacity, however, and can overflow (that is, drop segments) in theevent of sustained network congestion.In addition to TCP and UDP, Internet Control Message Protocol (ICMP) isanother transport layer protocol you are likely to encounter. ICMP is used byutilities such as ping and traceroute, which are discussed in Chapter 10,―Using Command-Line Utilities.‖Layer 5: The Session LayerThe session layer, as shown in Figure 2-12, is responsible for setting up,maintaining, and tearing down sessions. A session can be thought of as aconversation that needs to be treated separately from other sessions to avoidintermingling of data from different conversations. Figure 2-12 Layer 5: The Session Layer
• Setting up a session: Examples of the procedures involved in setting up asession include:• Checking user credentials (for example, username and password)• Assigning numbers to a session’s communications flows to uniquely identifyeach flow• Negotiating services required during the session• Negotiating which device begins sending data• Maintaining a session: Examples of the procedures involved inmaintaining a session include:• Transferring data• Reestablishing a disconnected session• Acknowledging receipt of data• Tearing down a session: A session can be disconnected based on mutualagreement of the devices in the session. Alternately, a session might be torndown because one party disconnects (either intentionally or because of anerror condition). In the event that one party disconnects, the other party candetect a loss of communication with that party and tear down its side of thesession.
Table of ContentsTitle PageCopyright PageAcknowledgementsAbout the AuthorIntroductionChapter 1 - Basic IOS Commands
Booting the Router Configuring a Router Using the show CommandChapter 2 - Managing a Cisco Internetwork Understanding the Internal Components of a Cisco Router Managing the Configuration Register Backing Up and Restoring the Cisco IOS Backing Up and Restoring the Cisco Configuration Using Cisco Discovery Protocol (CDP) Using Telnet Resolving Hostnames Checking Network Connectivity and Troubleshooting Using the sh processes CommandChapter 3 - IP Routing Routing Basics Routing Protocol Basics Routing Information Protocol (RIP)Chapter 4 - Enhanced IGRP (EIGRP) and Open Shortest Path First (OSPF) Understanding EIGRP Basics Understanding Open Shortest Path First (OSPF) Basics Configuring OSPF Verifying OSPF ConfigurationChapter 5 - Layer-2 Switching and Spanning-Tree Protocol (STP) Switching ServicesChapter 6 - Virtual LANs (VLANs) Understanding VLAN Basics Configuring VLANs Configuring VTP Telephony: Configuring Voice VLANsChapter 7 - Security
Perimeter Routers, Firewalls, and Internal Routers Introduction to Access Lists Standard Access Lists Extended Access Lists Monitoring Access ListsChapter 8 - Network Address Translation (NAT) When Do We Use NAT? Types of Network Address Translation NAT Names Configuring NAT Using SDMChapter 9 - Cisco’s Wireless Technologies Introducing Wireless Technology Configuring Cisco Wireless Using the IOS Configuring Cisco Wireless Using the SDM/HTTPChapter 10 - Internet Protocol Version 6 (IPv6) Why Do We Need IPv6? IPv6 Addressing and Expressions IPv6 Routing Protocols Migrating to IPv6 Verifying RIPng Verifying OSPFv3Chapter 11 - Wide Area Networks (WANs) Introduction to Wide Area Networks High-Level Data-Link Control (HDLC) Protocol Point-to-Point Protocol (PPP) Introduction to Frame Relay TechnologyChapter 12 - Cisco’s Security Device Manager (SDM) Configuring Your Router to Be Set Up Through the SDM Using the SDM to Manage the Flash Memory Using the SDM to Back Up, Restore, and Edit the Router’s Configuration Configuring LAN and WAN Interfaces and Verifying a Router Using SDM
Configuring RIP on a Router with SDM Configuring OSPF with the SDM What Does This Book Cover?This book covers everything you need to know in order to understand theCCNA exam objective commands. However, taking the time to study andpractice with routers or a router simulator is the real key to success. You will learn the following information in this book:• Chapter 1 introduces you to the Cisco Internetwork Operating System (IOS)and command-line interface (CLI). In this chapter you will learn how to turnon a router and configure the basics of the IOS, including setting passwords,banners, and more. IP configuration using the Secure Device Manager (SDM)will be discussed in Chapter 12.• Chapter 2 provides you with the management skills needed to run a CiscoIOS network. Backing up and restoring the IOS, as well as routerconfiguration, are covered, as are the troubleshooting command toolsnecessary to keep a network up and running. Chapter 12 will provide you theSDM configuration covered in this chapter.• Chapter 3 teaches you about IP routing. This is an important chapter,because you will learn how to build a network, add IP addresses, and routedata between routers. You will also learn about static, default, and dynamicrouting using RIP and RIPv2 (with a small touch of IGRP).• Chapter 4 dives into more complex dynamic routing with Enhanced IGRPand OSPF routing.• Chapter 5 gives you a background on layer-2 switching and how switchesperform address learning and make forwarding and filtering decisions.Network loops and how to avoid them with the Spanning Tree Protocol (STP)will be discussed, as well as the 802.1w STP version.• Chapter 6 covers virtual LANs and how you can use them in yourinternetwork. This chapter also covers the nitty-gritty of VLANs and thedifferent concepts and protocols used with VLANs, as well as troubleshooting.• Chapter 7 covers security and access lists, which are created on routers tofilter the network. IP standard, extended, and named access lists are coveredin detail.• Chapter 8 covers Network Address Translation (NAT). New information andall the configuration commands, troubleshooting, and verification commandsneeded to understand the NAT CCNA objectives are covered in this chapter.• Chapter 9 covers wireless technologies. This is an introductory chapterregarding wireless technologies as Cisco views wireless. Make sure youunderstand your basic wireless technologies such as access points and clientsas well as the difference between 802.11a, b, and g. This chapter is more
technology based than configuration based to cover the current CCNAobjectives.• Chapter 10 covers IPv6. This is a very fun chapter and has some greatinformation. IPv6 is not the big, bad scary monster that most people think itis. IPv6 is an objective on this new exam, so study this chapter carefully. Thischapter is more technology based then configuration based to cover thecurrent CCNA objectives. Keep an eye out at www.lammle.com for up-to-the-minute updates.• Chapter 11 concentrates on Cisco wide area network (WAN) protocols. Thischapter covers HDLC, PPP, and Frame Relay in depth. You must be proficientin all these protocols to be successful on the CCNA exam.• Chapter 12 covers SDM for basic router configures that we covered inChapters 1, 2, 3, and 4.For up-to-the minute updates covering additions or modifications to theCCNA certification exams, as well as additional study tools and reviewquestions, be sure to visit the Todd Lammle forum and websiteat www.lammle.com or www.sybex.com/go/ccnafastpass. Cisco Certified Network Associate (CCNA)The CCNA certification was the first in the new line of Cisco certifications andwas the precursor to all current Cisco certifications. Now you can become aCisco Certified Network Associate for the meager cost of this book and eitherone test at $150 or two tests at $125 each—although the CCNA exams areextremely hard and cover a lot of material, so you have to really know yourstuff! Taking a Cisco class or spending months with hands-on experience isnot out of the norm. Once you have your CCNA, you don’t have to stop there—you can choose tocontinue with your studies and achieve a higher certification, called the CiscoCertified Network Professional (CCNP). Someone with a CCNP has all theskills and knowledge he or she needs to attempt the routing and switchingCCIE lab. Just becoming a CCNA can land you that job you’ve dreamed about. Why Become a CCNA?Cisco, not unlike Microsoft and Novell (Linux), has created the certificationprocess to give administrators a set of skills and to equip prospectiveemployers with a way to measure skills or match certain criteria. Becoming a
CCNA can be the initial step of a successful journey toward a new, highlyrewarding, sustainable career. The CCNA program was created to provide a solid introduction not only tothe Cisco Internetwork Operating System (IOS) and Cisco hardware but alsoto internetworking in general, making it helpful to you in areas that are notexclusively Cisco’s. At this point in the certification process, it’s not unrealisticthat network managers—even those without Cisco equipment—require Ciscocertifications for their job applicants. If you make it through the CCNA and are still interested in Cisco andinternetworking, you’re headed down a path to certain success. What Skills Do You Need to Become a CCNA?To meet the CCNA certification skill level, you must be able to understand ordo the following:• A CCNA certified professional can install, configure, and operate LAN, WAN,and wireless access services securely, as well as troubleshoot and configuresmall to medium networks (500 nodes or fewer) for performance.• This knowledge includes, but is not limited to, use of these protocols: IP,IPv6, EIGRP, RIP, RIPv2, OSPF, serial connections, Frame Relay, cable, DSL,PPPoE, LAN switching, VLANs, Ethernet, security, and access lists. How Do You Become a CCNA?The way to become a CCNA is to pass one little test (CCNA Composite exam640-802). Then—poof!—you’re a CCNA. (Don’t you wish it were that easy?)True, it can be just one test, but you still have to possess enough knowledge tounderstand what the test writers are saying. However, Cisco has a two-step process that you can take in order to becomea CCNA that may or may not be easier than taking one longer exam (this bookis based on the one-step 640-802 method; however, this book has all theinformation you need to pass all three exams. The two-step method involves passing the following:• Exam 640-822: Interconnecting Cisco Networking Devices 1(ICND1)• Exam 640-816: Introduction to Cisco Networking Devices 2 (ICND2) I can’t stress this enough: It’s critical that you have some hands-onexperience with Cisco routers. If you can get ahold of some 1841 or 2800series routers, you’re set. But if you can’t, I’ve worked hard to providehundreds of configuration examples throughout this book to help networkadministrators (or people who want to become network administrators) learnwhat they need to know to pass the CCNA exam.
Since the new 640-802 exam is so hard, Cisco wants to reward you fortaking the two-test approach. Or so it seems anyway. If you take the ICND1exam, you actually receive a certification called the Cisco Certified EntryNetworking Technician (CCENT). This is one step toward your CCNA. Toachieve your CCNA, you must still pass your ICND2 exam. Again, this book is written to help you study for all three exams.For Cisco-authorized hands-on training with CCSI Todd Lammle, pleasesee www.globalnettraining.com. Each student will get hands-on experience byconfiguring at least three routers and two switches—no sharing of equipment! Where Do You Take the Exams?You may take any of the CCNA exams at any of the Pearson VUE authorizedcenters (www.vue.com) or call (877) 404-EXAM (3926). To register for a Cisco Certified Network Associate exam, follow these steps:1. Determine the number of the exam you want to take.2. Register with the nearest Pearson VUE testing center. At this point, you willbe asked to pay in advance for the exam. At the time of this writing, the examfor the 640-802 is $150 and must be taken within one year of payment. Youcan schedule exams up to six weeks in advance or as late as the same day youwant to take it—but if you fail a Cisco exam, you must wait five days before youwill be allowed to retake the exam. If something comes up and you need tocancel or reschedule your exam appointment, contact Pearson VUE at least 24hours in advance.3. When you schedule the exam, you’ll get instructions regarding allappointment and cancellation procedures, the ID requirements, andinformation about the testing-center location. Tips for Taking Your CCNA ExamsThe CCNA Composite exam test contains about 55 questions and must becompleted in 75 to 90 minutes or less. This information can change per exam.You must get a score of about 80 to 85 percent to pass this exam, but again,each exam can be different. Many questions on the exam have answer choices that at first glance lookidentical—especially the syntax questions! Remember to read through thechoices carefully because close doesn’t cut it. If you get commands in thewrong order or forget one measly character, you’ll get the question wrong. So,
to practice, do the hands-on exercises at the end of this book’s chapters overand over again until they feel natural to you. Also, never forget that the right answer is the Cisco answer. In many cases,more than one appropriate answer is presented, but the correct answer is theone that Cisco recommends. On the exam, you’re always instructed to pickone, two, or three, never ―choose all that apply.‖ The latest CCNA exams mayinclude the following test formats:• Multiple-choice single answer• Multiple-choice multiple answer• Drag-and-drop• Fill-in-the-blank• Router simulations In addition to multiple choice and fill-in response questions, Cisco CareerCertifications exams may include performance simulation exam items. Theydo allow partial command responses. For example, show config, sho config, orsh conf would be acceptable. Router#show ip protocol or router#show ip protwould be acceptable. Here are some general tips for exam success:• Arrive early at the exam center so you can relax and review your studymaterials.• Read the questions carefully. Don’t jump to conclusions. Make sure you’reclear about exactly what each question asks.• When answering multiple-choice questions that you’re not sure about, usethe process of elimination to get rid of the obviously incorrect answers first.Doing this greatly improves your odds if you need to make an educated guess.• You can no longer move forward and backward through the Cisco exams, sodouble check your answer before clicking Next since you can’t change yourmind. After you complete an exam, you’ll get immediate, online notification ofyour pass or fail status, a printed Examination Score Report that indicatesyour pass or fail status, and your exam results by section. (The testadministrator will give you the printed score report.) Test scores areautomatically forwarded to Cisco within five working days after you take thetest, so you don’t need to send your score to them. If you pass the exam, you’llreceive confirmation from Cisco, typically within two to four weeks,sometimes longer.This book covers everything CCNA related. For up-to-date information onTodd Lammle Cisco Authorized CCNA CCNP, CCSP, CCVP, and CCIE bootcamps, please see www.lammle.com orwww.globalnettraining.com.
How to Contact the AuthorYou can reach Todd Lammle through GlobalNet Training Solutions, Inc.,(www.globalnettraining.com), his training and systems Integration Companyin Dallas, Texas—or through his forum at www.lammle.com. Chapter 1 Basic IOS CommandsThis book starts by introducing you to the Cisco Internetwork OperatingSystem (IOS). The IOS is what runs Cisco routers as well as some Ciscoswitches, and it’s what allows you to configure the devices. You use thecommand-line interface (CLI) to configure a router, and that is what I’ll showyou in this chapter. The Cisco router IOS software is responsible for the following importanttasks:• Carrying network protocols and functions• Connecting high-speed traffic between devices• Adding security to control access and stop unauthorized network use• Providing scalability for ease of network growth and redundancy• Supplying network reliability for connecting to network resources You can access the Cisco IOS through the console port of a router, from amodem into the auxiliary (or aux) port, or even through Telnet and SecureShell (SSH). Access to the IOS command line is called an exec session. Once you have attached your console cable (this is a rolled cable, sometimesreferred to as a rollover cable) to the router and have started your terminalsoftware, you will be ready to power on the router. Assuming that this is a newrouter, it will have no configuration and thus will need to have, well,everything set up. In this chapter, first I’ll cover the power-on process of therouter, and then I’ll introduce the setup script.For up-to-the minute updates for this chapter, please seewww.lammle.com Booting the Router
The following messages appear when you first boot or reload a router: Notice the following in the previous messages:• The type of router (2811) and the amount of memory (262,144KB)• The version of software the router is running (12.4, 13)• The interfaces on the router (two Fast Ethernet and four serial) Figure 1.1 shows a picture of an 1841 router, which is what is calledanintegrated services router (ISR), just like the 2811 router output shownearlier.FIGURE 1.1 A Cisco 1841 router
An 1841 router holds most of the same interfaces as a 2800 router, but it’ssmaller and less expensive. Setup ModeIf the router has no initial configuration, you will be prompted to use setupmode to establish an initial configuration. You can also enter setup mode atany time from the command line by typing the command setup fromsomething calledprivileged mode. Setup mode covers only some globalcommands and is generally just not helpful. Here is an example:You can exit setup mode at any time by pressing Ctrl+C. Router Configuration ModesOne key to navigating the CLI is to always be aware of which routerconfiguration mode you are currently in (see Table 1.1). You can tell whichconfiguration mode you are in by watching the CLI prompt.
TABLE 1.1 Router Configuration Modes Once you understand the different modes, you will need to be able to movefrom one mode to another within the CLI. The commands in Table 1.2 allowyou to navigate between the assorted CLI modes.TABLE 1.2 Moving Between Modes Editing and Help FeaturesOne difference between a good and a great CLI engineer is the ability toquickly edit the line being entered into the router. Great CLI engineers canquickly recall previously entered commands and modify them, which is oftenmuch quicker than reentering the entire command. Table 1.3 shows some ofthe editing commands most commonly used.
TABLE 1.3 CLI Editing Commands The CLI also provides extensive online help. Any great CLI engineer willhave an excessively worn question-mark key on the keyboard! Table 1.4 showssome examples of using the online help.TABLE 1.4 Online Help Commands
Using the Question MarkThe only command is the question mark; however, it does make a differencewhere you use it. When entering complex IOS commands, it is common to usethe question mark repeatedly while entering the command, as in the followingexample:Using the PipeThe pipe (|) allows you to wade through all the configurations or other longoutputs and get straight to your goods fast. Table 1.5 shows the pipecommands.TABLE 1.5 Pipe Commands Here’s an example of using the pipe command to view just interfaceinformation on a router:
Configuring a RouterIn the following sections, I’ll introduce the commands used to do basic routerconfiguration. You’ll use these commands (or should use them) on everyrouter you configure. HostnamesYou can set the identity of the router with the hostname command. This isonly locally significant, which means it has no bearing on how the routerperforms name lookups or how the router works on the internetwork. Table1.6 shows the command for setting a router’s hostname.TABLE 1.6 Setting a Router Hostname Here’s an example of setting a hostname on a router: BannersYou can create a banner to give anyone who shows up on the router exactly theinformation you want them to have. Make sure you’re familiar with these fouravailable banner types: exec process creation banner, incoming terminal line
banner, login banner, and message of the day banner (all illustrated in Table1.7).TABLE 1.7 Setting a Banner The following describes the various banners:MOTD banner The MOTD banner will be displayed whenever anyoneattaches to the router, regardless of how they access the router.Exec banner You can configure a line activation (exec) banner to bedisplayed when an EXEC process (such as a line activation or incomingconnection to a VTY line) is created. By simply starting a user exec sessionthrough a console port, you’ll activate the exec banner.Incoming banner You can configure a banner to be displayed on terminalsconnected to reverse Telnet lines. This banner is useful for providinginstructions to users who use reverse Telnet.Login banner You can configure a login banner to be displayed on allconnected terminals. This banner is displayed after the MOTD banner butbefore the login prompts. The login banner can’t be disabled on a per-linebasis, so to globally disable it, you have to delete it with the no banner logincommand. PasswordsYou can use five passwords to secure your Cisco routers: console, auxiliary,Telnet (VTY), enable password, and enable secret. However, other commandsare necessary to complete the password configurations on a router or switch,as shown in Table 1.8.
TABLE 1.8 Setting PasswordsSetting PasswordsHere’s an example of setting all your passwords and then encrypting them inthe plain configuration file:
Some other console helpful commands include the following. Thissets the console timeout in second and minutes from 0-35791: This redisplays interrupted console input:
Here’s an example of setting the exec-timeout and logging synchronouscommands:Setting Up Secure Shell (SSH)Instead of Telnet, you can use Secure Shell, which creates a more securesession than the Telnet application that uses an unencrypted data stream. SSHuses encrypted keys to send data so that your username and password are notsent in the clear. Table 1.9 lists the commands.TABLE 1.9 SSH Commands Here’s an example of how you set up SSH on a router:1. Set your hostname:2. Set the domain name (both the hostname and domain name are requiredfor the encryption keys to be generated):3. Generate the encryption keys for securing the session:
4. Set the maximum idle timer for an SSH session:5. Set the maximum failed attempts for an SSH connection:6. Connect to the VTY lines of the router:7. Last, configure SSH and then Telnet as access protocols: If you do not use the keyword tel net at the end of the command string, thenonly SSH will work on the router. I suggest that you use just SSH if at allpossible. Telnet is just too insecure for today’s networks.
Contents at a GlanceIntroduction1 Network Infrastructure Design2 Advanced Router Configuration I3 Advanced Router Configuration II4 Configuring Juniper Routers5 Configuring and Managing the Network Infrastructure6 Analyzing Network Data Traffic7 Network Security8 IPv69 Linux Networking 10 Internet Routing 11 Voice over IPGlossaryIndexTable of ContentsIntroductionChapter 1 Network Infrastructure DesignChapter OutlineObjectivesKey TermsIntroduction1-1 Physical Network DesignCoreDistribution LayerAccess LayerData FlowSelecting the Media1-2 IP Subnet DesignIP Address RangeDetermining the Number of Subnetworks Needed for the NetworkDetermining the Size or the Number of IP Host Addresses Needed for theNetworkIP Assignment1-3 VLAN NetworkVirtual LAN (VLAN)VLAN ConfigurationVLAN Tagging802.1Q ConfigurationNetworking Challenge: Static VLAN Configuration
Configuring the HP Procurve Switch1-4 Routed NetworkRouterGateway AddressNetwork SegmentsMultilayer SwitchLayer 3 Routed NetworksRouted Port ConfigurationInterVLAN Routing ConfigurationSerial and ATM Port ConfigurationSummaryQuestions and ProblemsChapter 2 Advanced Router Configuration IChapter OutlineObjectivesKey TermsIntroduction2-1 Configuring Static RoutingGateway of Last ResortConfiguring Static RoutesLoad Balancing and RedundancyNetworking Challenge—Static Routes2-2 Dynamic Routing ProtocolsDistance Vector ProtocolsLink State Protocols2-3 Configuring RIPv2Configuring Routes with RIPConfiguring Routes with RIP Version 2Networking Challenge—RIP2-4 TFTP—Trivial File Transfer ProtocolConfiguring TFTPSummaryQuestions and ProblemsChapter 3 Advanced Router Configuration IIChapter OutlineObjectivesKey TermsIntroduction3-1 Configuring Link State Protocols—OSPFLink State ProtocolsConfiguring Routes with OSPFLoad Balancing and Redundancy with OSPF
Networking Challenge—OSPF3-2 Configuring Link State Protocols—IS-ISConfiguring Routes with IS-ISLoad Balancing and Redundancy with IS-ISNetworking Challenge: IS-IS3-3 Configuring Hybrid Routing Protocols—EIGRPConfiguring Routes with EIGRPLoad Balancing and RedundancyNetworking Challenge: EIGRP3-4 Advanced Routing RedistributionRoute Redistribution into RIPRoute Redistribution into OSPFRoute Redistribution into EIGRPRoute Redistribution into IS-IS3-5 Analyzing OSPF ―Hello‖ PacketsSummaryQuestions and ProblemsChapter 4 Configuring Juniper RoutersChapter OutlineObjectivesKey TermsIntroduction4-1 Operational Mode4-2 Router Configuration ModeDisplaying the Router InterfacesHostname ConfigurationAssigning an IP Address to an Interface4-3 Configuring Routes on Juniper RoutersConfigure STATIC Routes on Juniper RoutersConfigure RIP on Juniper RoutersConfigure OSPF on Juniper RoutersConfigure IS-IS on Juniper Routers4-4 Configuring Route Redistribution on Juniper RoutersSummaryQuestions and ProblemsChapter 5 Configuring and Managing the Network InfrastructureChapter OutlineObjectivesKey TermsIntroduction5-1 Domain Name and IP Assignment5-2 IP Management with DHCP
DHCP Data PacketsDHCP Deployment5-3 Scaling the Network with NAT and PATConfiguring NAT5-4 Domain Name Service (DNS)DNS Tree HierarchyDNS Resource RecordsSummaryQuestions and ProblemsChapter 6 Analyzing Network Data TrafficChapter OutlineObjectivesKey TermsIntroduction6-1 Protocol Analysis/ForensicsBasic TCP/UDP ForensicsARP and ICMP6-2 Wireshark Protocol AnalyzerUsing Wireshark to Capture Packets6-3 Analyzing Network Data TrafficConfiguring SNMPNetFlow6-4 FilteringFTP FilteringRight-Click Filtering Logic RulesFiltering DHCPSummaryQuestions and ProblemsChapter 7 Network SecurityChapter OutlineObjectivesKey TermsIntroduction7-1 Denial of ServiceDistributed Denial of Service Attacks (DDoS)7-2 Firewalls and Access ListsNetwork Attack PreventionAccess Lists7-3 Router SecurityRouter AccessRouter ServicesRouter Logging and Access-List
7-4 Switch SecuritySwitch Port SecuritySwitch Special Features7-5 Wireless Security7-6 VPN SecurityVPN Tunneling ProtocolsConfiguring a VPN Virtual Interface (Router to Router)Troubleshooting the VPN Tunnel LinkSummaryQuestions and ProblemsChapter 8 IPv6Chapter OutlineObjectivesKey TermsIntroduction8-1 Comparison of IPv6 and IPv48-2 IPv6 Addressing8-3 IPv6 Network Settings8-4 Configuring a Router for IPv68-5 IPv6 RoutingIPv6: StaticIPv6: RIPIPv6: OSPFIPv6: EIGRPIPv6: IS-IS8-6 Troubleshooting IPv6 ConnectionSummaryQuestions and ProblemsChapter 9 Linux NetworkingChapter OutlineObjectivesKey TermsIntroduction9-1 Logging On to LinuxAdding a User Account9-2 Linux File Structure and File CommandsListing FilesDisplaying File ContentsDirectory OperationsFile OperationsPermissions and Ownership9-3 Linux Administration Commands
The man (manual) CommandThe ps (processes) CommandThe su (substitute user) CommandThe mount CommandThe shutdown CommandLinux Tips9-4 Adding Applications to Linux9-5 Linux NetworkingInstalling SSHThe FTP ClientDNS Service on LinuxChanging the Hostname9-6 Troubleshooting System and Network Problems with LinuxTroubleshooting Boot ProcessesListing Users on the SystemNetwork SecurityEnabling and Disabling Boot Services9-7 Managing the Linux SystemSummaryQuestions and Problems Chapter 10 Internet RoutingChapter OutlineObjectivesKey TermsIntroduction10-1 Internet Routing—BGPConfiguring a WAN ConnectionConfiguring an Internet Connection10-2 Configuring BGPConfiguring BGPNetworking Challenge: BGP10-3 BGP Best Path Selection10-4 IPv6 over the Internet10-5 Configure BGP on JUNIPER RoutersSummaryQuestions and Problems Chapter 11 Voice over IPChapter OutlineObjectivesKey TermsIntroduction11-1 The Basics of Voice over IP
11-2 Voice over IP NetworksReplacing an Existing PBX Tie LineUpgrading Existing PBXs to Support IP TelephonySwitching to a Complete IP Telephony Solution11-3 Quality of ServiceJitterNetwork LatencyQueuingQOS Configuration Example11-4 Analyzing VoIP Data PacketsAnalyzing VoIP Telephone Call Data Packets11-5 VoIP SecuritySummaryQuestions and ProblemsKey Terms GlossaryIndexAbout the AuthorsJeffrey S. Beasley is with the Department of Engineering Technology andSurveying Engineering at New Mexico State University. He has been teachingwith the department since 1988 and is the co-author of Modern ElectronicCommunication and Electronic Devices and Circuits, and the authorofNetworking.Piyasat Nilkaew is a network engineer with 15 years of experience innetwork management and consulting, and has extensive expertise indeploying and integrating multiprotocol and multivendor data, voice, andvideo network solutions on limited budgets.Dedications This book is dedicated to my family, Kim, Damon, and Dana. —Jeff Beasley This book is dedicated to Jeff Harris and Norma Grijalva. Not only have you given me my networking career, but you are also my mentors. You inspire me to think outside the box and motivate me to continue improving my skills. Thank you for giving me the opportunity of a lifetime. I am very grateful. —Piyasat NilkaewAcknowledgmentsI am grateful to the many people who have helped with this text. My sincerethanks go to the following technical consultants:
• Danny Bosch and Matthew Peralta for sharing their expertise with opticalnetworks and unshielded twisted-pair cabling, and Don Yates for his help withthe initial Net-Challenge Software.• Abel Sanchez, for his review of the Linux Networking chapter.I also want to thank my many past and present students for their help withthis book:• David Potts, Jonathan Trejo, and Nate Murillo for their work on the Net-Challenge Software. Josiah Jones, Raul Marquez Jr., Brandon Wise, and ChrisLascano for their help with the Wireshark material. Also, thanks to WayneRandall and Iantha Finley Malbon for the chapter reviews.Your efforts are greatly appreciated.I appreciate the excellent feedback of the following reviewers: Phillip Davis,DelMar College, TX; Thomas D. Edwards, Carteret Community College, NC;William Hessmiller, Editors & Training Associates; Bill Liu, DeVry University,CA; and Timothy Staley, DeVry University, TX.My thanks to the people at Pearson for making this project possible: DaveDusthimer, for providing me with the opportunity to work on this book, andVanessa Evans, for helping make this process enjoyable. Thanks to BrettBartow, Christopher Cleveland, and all the people at Pearson, and to the manytechnical editors for their help with editing the manuscript.Special thanks to our families for their continued support and patience.—Jeffrey S. Beasley and Piyasat NilkaewAbout the Technical ReviewersWayne Randall started working in the Information Technology field in 1994at Franklin Pierce College (now Franklin Pierce University) in Rindge, NH,before becoming a Microsoft Certified Trainer and a consultant at EnterpriseTraining and Consulting in Nashua, NH.Wayne acquired his first certification in Windows NT 3.51 in 1994, became anMCSE in NT 4.0 in 1996, was a Certified Enterasys Network SwitchingEngineer in 2000, and then worked as a networking and systems consultantfrom 2001 to 2006 before becoming a director of IT for a privately heldcompany. Wayne currently works for Bodycote, PLC, as a networkengineer/solutions architect. Bodycote has 170 locations across 27 countrieswith 43 locations in North America. Wayne has taught for Lincoln Educationsince 2001 and developed curricula for it since 2011. Mr. Randall holds a BA inAmerican Studies from Franklin Pierce University.Iantha Finley Malbon’s teaching career has spanned 20 years from middleschool to collegiate settings and is currently a CIS professor at Virginia UnionUniversity. She is also an adjunct professor at ECPI University, havingpreviously served as CIS Department Chair, teaching Cisco routing,networking, and Information Technology courses. She implemented the Cisco
Academy for Hanover Schools and was the CCAI for the Academy. She earnedher master’s degree in Information Systems from Virginia CommonwealthUniversity and bachelor’s degree in Technology Education from Virginia Tech.She holds numerous certifications including CCNA, Network+, A+, and FiberOptic Technician.We Want to Hear from You!As the reader of this book, you are our most important critic andcommentator. We value your opinion and want to know what we’re doingright, what we could do better, what areas you’d like to see us publish in, andany other words of wisdom you’re willing to pass our way.As the associate publisher for Pearson IT Certification, I welcome yourcomments. You can email or write me directly to let me know what you did ordidn’t like about this book—as well as what we can do to make our booksbetter.Please note that I cannot help you with technical problems related to thetopic of this book. We do have a User Services group, however, where I willforward specific technical questions related to the book.When you write, please be sure to include this book’s title and author as wellas your name, email address, and phone number. I will carefully review yourcomments and share them with the author and editors who worked on thebook.Email: firstname.lastname@example.orgMail: Dave Dusthimer Associate Publisher Pearson IT Certification 800 East 96th Street Indianapolis, IN 46240 USAReader ServicesVisit our website and register this book atwww.pearsonitcertification.com/register for convenient access to any updates,downloads, or errata that might be available for this book.IntroductionThis book looks at advanced computer networking. It first guides readersthrough network infrastructure design. The readers are then introduced toconfiguring static, RIPv2, OSPF, ISIS, EIGRP routing protocols, techniquesfor configuring Juniper router, managing the network infrastructure,analyzing network data traffic using Wireshark, network security, IPv6, Linuxnetworking, Internet routing, and Voice over IP. After covering the entire text,
readers will have gained a solid knowledge base in advanced computernetworks.In my years of teaching, I have observed that technology students prefer tolearn ―how to swim‖ after they have gotten wet and taken in a little water.Then, they are ready for more challenges. Show the students the technology,how it is used, and why, and they will take the applications of the technologyto the next level. Allowing them to experiment with the technology helps themto develop a greater understanding. This book does just that.Organization of the TextThis textbook is adapted from the second edition of Networking. This thirdvolume has been revised and reorganized around the needs of advancednetworking students. This book assumes that the students have beenintroduced to the basics of computer networking. Throughout the text, thestudents are introduced to more advanced computer networking concepts.This involves network infrastructure design, advanced router configuration,network security, analyzing data traffic, Internet routing, and Voice over IP.Key Pedagogical Features• Chapter Outline, Key Terms, and Introduction at the beginning of eachchapter clearly outline specific goals for the reader. An example of thesefeatures is shown in Figure P-1.
Figure P-1• Net-Challenge Software provides a simulated, hands-on experience inconfiguring routers and switches. Exercises provided in the text (see Figure P-2) and on the CD challenge readers to undertake certain router/ networkconfiguration tasks. The challenges check the students’ ability to enter basicnetworking commands and set up router function, such as configuring theinterface (Ethernet and Serial) and routing protocols (that is, static, RIPv2,OSPF, ISIS, EIGRP, BGP, and VLANs). The software has the look and feel ofactually being connected to the router’s and switch console port.
Figure P-2• The textbook features and introduces how to use the Wireshark NetworkProtocol Analyzer. Examples of using the software to analyze data traffic areincluded throughout the text, as shown inFigure P-3.
Figure P-3• Numerous worked-out examples are included in every chapter to reinforcekey concepts and aid in subject mastery, as shown in Figure P-4.
Figure P-4• Key Terms and their definitions are highlighted in the margins to fosterinquisitiveness and ensure retention. This is illustrated inFigure P-5.
Figure P-5• Extensive Summaries, Questions, and Problems, as well as Critical ThinkingQuestions, are found at the end of each chapter, as shown inFigure P-6.
Figure P-6• An extensive Glossary is found at the end of this book and offers quick,accessible definitions to key terms and acronyms, as well as an exhaustiveIndex (see Figure P-7).
Figure P-7Accompanying CD-ROMThe CD-ROM packaged with the text includes the captured data packets usedin the text. It also includes the Net-Challenge Software, which was developedspecifically for this text.Instructor ResourcesThe Instructor’s Manual to accompany A Practical Guide to AdvancedNetworking, (ISBN: 978-0-132-88303-0) provides the entire book in PDFformat along with instructor notes for each section within each chapter,recommending key concepts that should be covered in each chapter. Solutionsto all Chapter Questions and Problems sections are also included. In addition,the instructor can also access 13 lab and lab-related exercises and a test bankwith which to generate quizzes on the material found within the studentedition of the book.Chapter 1. Network Infrastructure DesignChapter OutlineIntroduction
1-1 Physical Network Design1-2 IP Subnet Design1-3 VLAN Network1-4 Routed NetworkSummaryQuestions and ProblemsObjectives• Understand the purpose of the three layers of a campus network design• Understand the issue of data flow and selecting the network media• Develop techniques for IP allocation and subnet design• Understand the process of configuring a VLAN• Understand the issues of configuring the Layer 3 routed networkKey Termscoredistribution layeraccess layerCIDRISPintranetsNATPATOverloadingsupernetgatewaybroadcast domainflat networkVLAN (virtual LAN)port-based VLANtag-based VLANprotocol-based VLANVLAN ID802.1Qstatic VLANdynamic VLANshow vlanvlan databasevlan vlan_idshow vlan name vlan-nameinterface vlan 1show interface statustrunk portInter-Switch Link (ISL)
Switchport mode trunkswitchport trunk encapsulation dot1qswitchport trunk encapsulation islswitchport trunk allowed vlan vlan_idshow interfaces trunknetwork addresslogical addressrouter interfacerouting tablesubnet, NETmultilayer switch (MLS)wire speed routingrouted networkLayer 3 networkSONETWANterminal monitor (term mon)terminal no monitor (term no mon)show ip interface brief (sh ip int br)no switchportsecondary IP addressInterVLAN routingrouter on a stickSVIDSCSU/DSUAMIB8ZSMinimum Ones DensityHDLCPPPWICVWICservice-module t1show controller t1 slot/portATMVirtual Path Connection (VPC)Virtual Channel Connection (VCC)SVCVPIVCI
IntroductionThe objective of this chapter is to examine the computer networking issuesthat arise when planning a campus network. The term campusnetwork applies to any network that has multiple LANs interconnected. TheLANs are typically in multiple buildings that are close to each other andinterconnected with switches and routers. This chapter looks at the planningand designs of a simple campus network, including network design, IP subnetassignment, VLAN configuration, and routed network configuration.The basics of configuring the three layers of a campus LAN (core, distribution,and access) are first examined in Section 1-1. This section also addresses theimportant issues of data flow and selecting the proper network media. Section1-2 examines IP allocation and subnet design. Section 1-3 discusses the VLANnetwork, including a step-by-step process of how to configure a VLAN, whichprovides an introduction to the basic switch commands and the steps forconfiguring a static VLAN. Section 1-4 examines the Layer 3 routed network.This section explores the functions of the router and includes configurationexamples in different scenarios.1-1. Physical Network DesignMost campus networks follow a design that has core, distribution, and accesslayers. These layers, shown in Figure 1-1, can be spread out into more layers orcompacted into fewer, depending on the size of these networks. This three-layer network structure is incorporated in campus networks to improve datahandling and routing within the network. The issues of data flow and networkmedia are also examined in this section.
Figure 1-1. The core, distribution, and access layers of a campus networkCoreThe network core usually contains high-end Layer 3 switches or routers.Thecore is the heart, or backbone, of the network. The major portion of anetwork’s data traffic passes through the core. The core must be able toquickly forward data to other parts of the network. Data congestion should beavoided at the core, if possible. This means that unnecessary route policiesshould be avoided. An example of a route policy is traffic filtering, whichlimits what traffic can pass from one part of a network to another. Keep inmind that it takes time for a router to examine each data packet, andunnecessary route policies can slow down the network’s data traffic.CoreThe Backbone of the NetworkHigh-end routers and Layer 3 switches are typically selected for use in thecore. Of the two, the Layer 3 switch is the best choice. A Layer 3 switch isessentially a router that uses electronic hardware instead of software to makerouting decisions. The advantage of the Layer 3 switch is the speed at which itcan make a routing decision and establish a network connection.Another alternative for networking hardware in the core is a Layer 2 switch.The Layer 2 switch does not make any routing decisions and can quickly make
network connection decisions based on the network hardware connected to itsports. The advantage of using the Layer 2 switch in the core is cost. Thedisadvantage is that the Layer 2 switch does not route data packets; however,high-speed Layer 2 switches are more affordable than high-speed routers andLayer 3 switches.An important design issue in a campus network and the core isredundancy.Redundancy provides for a backup route or network connectionin case of a link failure. The core hardware is typically interconnected to alldistribution network hardware, as shown in Figure 1-1. The objective is toensure that data traffic continues for the entire network, even if a corenetworking device or link fails.Each layer beyond the core breaks the network into smaller networks with thefinal result being a group of networks that are capable of handling the amountof traffic generated. The design should thus incorporate some level ofredundancy.Distribution LayerThe distribution layer in the network is the point where the individualLANs connect to the campus network routers or Layer 3 switches. Routing andfiltering policies are more easily implemented at the distribution layer withouthaving a negative impact on the performance of the network data traffic. Also,the speed of the network data connections at the distribution layer is typicallyslower than at the core. For example, connection speeds at the core should bethe highest possible, such as 1 or 10 gigabits, where the data speed connectionsat the distribution layer could be 100 Mbps or 1 gigabit. Figure 1-1 shows theconnections to the access and core layers via the router’s Ethernet interfaces.Distribution LayerPoint where the individual LANs connect together.Access LayerThe access layer is where the networking devices in a LAN connect together.The network hardware used here is typically a Layer 2 switch. Remember, aswitch is a better choice because it forwards data packets directly todestination hosts connected to its ports, and network data traffic is notforwarded to all hosts in the network. The exception to this is a broadcastwhere data packets are sent to all hosts connected to the switch.Access LayerWhere the networking devices in a LAN connect together.
NoteHubs are not recommended at all in modern computer networks.Data FlowAn important networking issue is how data traffic flows in the core,distribution, and access layers of a campus LAN. In reference to Figure 1-1, ifcomputer A1 in LAN A sends data to computer D1 in LAN D, the data is firstsent through the switch in LAN A and then to Router A in the distributionlayer. Router A then forwards the data to the core switches, Switch A or SwitchB. Switch A or Switch B then forwards the data to Router C. The data packet isthen sent to the destination host in LAN D.The following are some questions often asked when setting up a network thatimplements the core, distribution, and access layers:• In what layer are the campus network servers (web, email, DHCP,DNS, and so on) located? This varies for all campus networks, and there isnot a definitive answer. However, most campus network servers are located inthe access layer.• Why not connect directly from Router A to Router C at thedistribution layer? There are network stability issues when routing largeamounts of network data traffic if the networks are fully or even partiallymeshed together. This means that connecting routers together in thedistribution layer should be avoided.• Where is the campus backbone located in the layers of a campusnetwork? The backbone of a campus network carries the bulk of the routeddata traffic. Based on this, the backbone of the campus network connects thedistribution and the core layer networking devices.Selecting the MediaThe choices for the media used to interconnect networks in a campus networkare based on several criteria. The following is a partial list of things toconsider:• Desired data speed• Distance for connections• BudgetThe desired data speed for the network connection is probably the firstconsideration given when selecting the network media. Twisted-pair cableworks well at 100 Mbps and 1 Gbps and is specified to support data speeds of10-gigabit data traffic. Fiber-optic cable supports LAN data rates up to 10Gbps or higher. Wireless networks support data rates up to 200+ Mbps.The distance consideration limits the choice of media. CAT 6/5e or better havea distance limitation of 100 meters. Fiber-optic cable can be run for manykilometers, depending on the electronics and optical devices used. Wireless
LAN connections can also be used to interconnect networks a few kilometersapart.The available budget is always the final deciding factor when planning thedesign for a campus LAN. If the budget allows, fiber-optic cable is probablythe best overall choice, especially in the high-speed backbone of the campusnetwork. The cost of fiber is continually dropping, making it more competitivewith lower-cost network media, such as twisted-pair cable. Also, fiber cablewill always be able to carry a greater amount of data traffic and can easily growwith the bandwidth requirements of a network.Twisted-pair cable is a popular choice for connecting computers in a wiredLAN. The twisted-pair technologies support bandwidths suitable for mostLANs, and the performance capabilities of twisted-pair cable is alwaysimproving.Wireless LANs are being used to connect networking devices together in LANswhere a wired connection is not feasible or mobility is the major concern. Forexample, a wireless LAN could be used to connect two LANs in a buildingtogether. This is a cost-effective choice if there is not a cable duct to run thecable to interconnect the LANs or if the cost of running the cable is too high.Also, wireless connections are playing an important role with mobile userswithin a LAN. The mobile user can make a network connection without havingto use a physical connection or jack. For example, a wireless LAN could beused to enable network users to connect their mobile computers to the campusnetwork.1-2. IP Subnet DesignOnce the physical infrastructure for a network is in place, the next big step isto plan and allocate IP space for the network. Take time to plan the IP subnetdesign, because it is not easy to change the IP subnet assignments once theyare in place. It is crucial for a network engineer to consider three factorsbefore coming up with the final IP subnet design. These three factors are1. The assigned IP address range2. The number of subnetworks needed for the network3. The size or the number of IP host addresses needed for the networkThe final steps in designing the IP subnet is to assign an IP address to theinterface that will serve as the gateway out of each subnet.IP Address RangeThe IP address range defines the size of the IP network you can work with. Insome cases, a classless interdomain routing (CIDR) block of public IPaddresses might be allocated to the network by an ISP. For example, the blockof IP address 184.108.40.206/24 could be assigned to the network. This caseallocates 256 IP addresses to the 220.127.116.11 network. In another case, aCIDR block of private IP addresses, like 10.10.10.0/24, could be used. In this
case, 256 IP addresses are assigned to the 10.10.10.0 network. For establishednetworks with an IP address range already in use, the network engineergenerally has to work within the existing IP address assignments. With abrand new network, the engineer has the luxury of creating a network fromscratch.In most network situations, an IP address block will have been previouslyassigned to the network for Internet use. The public IP addresses are typicallyobtained from the ISP (Internet service provider). This IP block of addressescould be from Class A, B, or C networks, as shown in Table 1-1. Table 1-1. Address Range for Each Class of NetworkCIDRClassless Interdomain RoutingISPInternet service provider: An organization that provides Internet access forthe public.Today, only public Class C addresses are assigned by ISPs, and most of themare not even a full set of Class C addresses (256 IP addresses). A lot of ISPspartition their allotted IP space into smaller subnets and then, in turn, providethose smaller portions to the customers. The bottom line is the limitednumber of public IP addresses are now a commodity on the Internet, and it isimportant to note that there are fees associated with acquiring an IP rangefrom an ISP.Not many institutions or businesses have the luxury of using public IPaddresses inside their network anymore. This is because the growing numberof devices being used in a network exceeds the number of public IP addressesassigned to them. The solution is that most networks are using private IPaddresses in their internal network. Private addresses are IP addresses setaside for use in privateintranets. An intranet is an internal internetwork thatprovides file and resource sharing. Private addresses are not valid addressesfor Internet use, because they have been reserved for internal use and are notroutable on the Internet. However, these addresses can be used within aprivate LAN (intranet) to create the internal IP network.
IntranetsInternetwork that provides file and resource sharing.NATNetwork Address Translation. A technique used to translate an internalprivate IP address to a public IP address.PATPort Address Translation. A port number is tracked with the client computer’sprivate address when translating to a public address.OverloadingWhere NAT translates the home network’s private IP addresses to a singlepublic IP address.The private IP addresses must be translated to public IP addresses usingtechniques like NAT (Network Address Translation) or PAT (Port AddressTranslation) before being routed over the Internet. For example, computer 1 inthe home network (see Figure 1-2) might be trying to establish a connection toan Internet website. The wireless router uses NAT to translate computer 1’sprivate IP address to the public IP address assigned to the router. The routeruses a technique called overloading, where NAT translates the homenetwork’s private IP addresses to the single public IP address assigned by theISP. In addition, the NAT process tracks a port number for the connection.This technique is called Port Address Translation (PAT). The router stores thehome network’s IP address and port number in a NAT lookup table. The portnumber differentiates the computer that is establishing a connection to theInternet because the router uses the same public address for all computers.This port number is used when a data packet is returned to the home network.This port number identifies the computer that established the Internetconnection, and the router can deliver the data packet back to the correctcomputer. An example of this conversion is provided in Figure 1-3. Thisexample shows three data connections originating from the home network of192.168.0.0/24. A single 18.104.22.168 IP address is used for the Internetconnection. Port address translation is being used to map the data packet backto the origination source. In this case, the port numbers are 1962, 1970, and1973.
Figure 1-2. An example of a home computer connecting to the ISP Figure 1-3. This example shows the three data connections originating from the home network of 192.168.0.0/24Determining the Number of Subnetworks Needed for the NetworkThe use of private IP addresses is a viable technique for creating a largeamount of IP addresses for intranet use. Obviously, there is a big differencewhen designing an IP network for a single network than there is whendesigning an IP network for multiple networks. When designing an IP networkfor one single network, things are quite simple. This type of configuration istypically found in the home, small office, or a small business environmentwhere one IP subnet is allocated and only one small router is involved.For situations requiring multiple networks, each network must be sizedaccordingly. Therefore, the subnet must be carefully designed. In addition,networks with multiple subnets require a router or multiple routers withmultiple routed network interfaces to interconnect the networks. For example,if the network engineer is using private addresses and needs to design forthree different networks, one possibility is to assign 10.10.10.0/24 for the first
network, 172.16.0.0/24 for the second network, and 192.168.1.0/24 for thethird network. Is this a good approach? Technically, this can be done, but it isprobably not logically sound. It makes more sense to group these networkswithin the same big CIDR block. This will make it easier for a networkengineer to remember the IP assignments and to manage the subnets. A betterdesign is to assign 10.10.10.0/24 to the first network, 10.10.20.0/24 to thesecond network, and 10.10.30.0/24 to the third network. All three networksare all in the same ―10‖ network, which makes it easier for the networkengineer to track the IP assignments. The term subnet and network are usedinterchangeably in multiple network environments. The term subnet usuallyindicates a bigger network address is partitioned and is assigned to smallernetworks or subnets.Another design factor that the network engineer must address is the networksize. Two questions that a good network engineer must ask are• How many network devices must be accommodated in the network?(Current demand)• How many network devices must be accommodated in the future? (Futuregrowth)Simply put, the IP network must be designed to accommodate the currentdemand, and it must be designed to accommodate future growth. Once thesize of a network is determined, a subnet can be assigned. In the case of asingle network, the design is not too complicated. For example, if the networkneeds to be able to accommodate 150 network devices, an entire Class Caddress, like 192.168.1.0/24, can be assigned to the network. This will handlethe current 150 network devices and leave enough room for growth. In thisexample, 104 additional IP address will be available for future growth.When allocating IP address blocks, a table like Table 1-2 can be used toprovide the CIDR for the most common subnet masks and their correspondingnumber of available IP addresses. Table 1-2. CIDR—Subnet Mask-IPs Conversion
Even with a much smaller network, like the home network, where only ahandful of network computers and peripherals are present, an entire Class Cprivate address is generally allocated to the home network. In fact, most homerouters are preconfigured with a private Class C address within the192.168.0.0–192.168.0.255 range. This technique is user friendly and easy touse and sets aside private IP addresses for internal network use. Thistechnique virtually guarantees that users will never have to worry aboutsubnetting the CIDR block.For a bigger network that must handle more than 254 network devices, asupernet can be deployed. A supernet is when two or more classful contiguousnetworks are grouped together. The technique of supernetting was proposedin 1992 to eliminate the class boundaries and make available the unused IPaddress space. Supernetting allows multiple networks to be specified by onesubnet mask. In other words, the class boundary could be overcome. For
example, if the network needs to be able to accommodate 300 networkdevices, two Class C networks, like 192.168.0.0/24 and 192.168.1.0/24, can begrouped together to form a supernet of 192.168.0.0/23, which canaccommodate up to 510 network devices. As shown in Table 1-2, a /23 CIDRprovides 512 available IP addresses. However, one IP is reserved for thenetwork address and another one is reserved for the network broadcastaddress. Therefore, a /23 CIDR yields 512 – 2 = 510 usable host IP addresses.SupernetTwo or more classful contiguous networks are grouped together.Determining the Size or the Number of IP Host Addresses Needed for theNetworkThe problem with randomly applying CIDR blocks to Class A, B, and Caddresses is that there are boundaries in each class, and these boundariescan’t be crossed. If a boundary is crossed, the IP address maps to anothersubnet. For example, if a CIDR block is expanded to include four Class Cnetworks, all four Class C networks need to be specified by the same CIDRsubnet mask to avoid crossing boundaries. The following example illustratesthis.Example 1-1Figure 1-4 shows three different networks with different size requirements.The needed capacity (number of devices) for each network is specified in thefigure. Your task is to determine the CIDR block required for each networkthat will satisfy the number of expected users. You are to use Class C private IPaddresses when configuring the CIDR blocks.
Figure 1-4. Three different networksSolution:For LAN A, a CIDR block that can handle at least 300 networking devicesmust be provided. In this case, two contiguous Class C networks of192.168.0.0/24 and 192.168.1.0/24 can be grouped together to form a192.168.0.0/23 network. Referring to Table 1-2, a /23 CIDR with a subnetmask of 255.255.254.0 provides 512 IP addresses which more than satisfiesthe required 300 networking devices.The next question is to determine what the network address is for LAN A. Thiscan be determined by ANDing the 255.255.254.0 subnet mask with192.168.0.0 and 192.168.1.0.This shows that applying the /23 [255.255.254.0] subnet mask to the specifiedIP address places both in the same 192.168.0.0 network. This also means thatthis CIDR block does not cross boundaries, because applying the subnet maskto each network address places both in the same 192.168.0.0 network.For LAN B1, the requirement is that a CIDR block that can handle 800network devices must be provided. According to Table 1-2, a /22 CIDR yields1,022 usable host IP addresses and is equivalent to grouping four Class Cnetworks together. Therefore, a /22 CIDR can be used.The next decision is selecting the group of IP addresses to create the CIDRblock and decide where the IP addresses should start. Recall that the192.168.0.0 and 192.168.1.0 networks are being used to create the LAN A
CIDR block. Should LAN B1 start from 192.168.2.0/22, which is the nextcontiguous space? The answer is no. The 192.168.2.0/22 is still within theboundary of the 192.168.0.0/23 network. Remember, the requirement is thata CIDR block that can handle 800 network devices must be provided and thatboundaries cannot be crossed, and the designer must be careful not to overlapthe networks when assigning subnets to more than one network. In this case,when the /22 subnet mask (255.255.252.0) is applied to 192.168.2.0, thisyields the network 192.168.0.0. The AND operation is shown:192. 168. 2. 0255. 255.252. 0 (/22)192. 168. 0. 0This happens to be the same network address as when the /23 CIDR subnetmask (255.255.254.0) is applied to any IP within the range of 192.168.0.0-192.168.1.255, as shown:There is an overlap between 192.168.0.0/23 and 192.168.2.0/22. Moving tothe next contiguous Class C of 192.168.3.0/22, we still find that it’s still in the192.168.0.0:192.168.3.02522.214.171.124 (/22)192.168.0.0 is still in the same subnet.Based on this information, the next Class C range 192.168.4.0/22 is selected.This yields a nonoverlapping network of 192.168.4.0, so the subnet192.168.4.0/22 is a valid for this network:192.168.4.025126.96.36.199 (/22)192.168.4.0 is not the same subnet; therefore, this is an acceptable CIDRblock.Recall that the CIDR for LANB1 is a /22 and is equivalent to grouping fourClass C networks. This means that LANB1 uses the following Class C networks:192.168.4.0192.168.5.0192.168.6.019188.8.131.52The IP subnet design gets more complicated when designing multiplenetworks with different size subnets. This generally means that the subnetmask or the CIDR will not be uniformly assigned to every network. Forexample, one network might be a /25 network or /22, while another is a /30network.
The next requirement is that a CIDR block that can handle 800 networkdevices must be tasked to assign a CIDR block to LAN B2. This LAN is a servernetwork that houses a fixed number of servers. The number is not expected togrow beyond 80 servers. One easy approach is to assign a /24 CIDR to thisnetwork.This means that the next network is 192.168.8.0/24, which is the nextnonoverlapping CIDR block after 192.168.4.0/22. The /24 CIDR gives 254host IP addresses, but only 80 IP addresses are required. Another approach isto size it appropriately. According to Table 1-2, a good CIDR to use is a /25,which allows for 126 host IP addresses. Therefore, a network 192.168.8.0/25can be used for this network.Assigning a 192.168.8.0/24 CIDR, which can accommodate 254 hosts, seemslike a waste, because the network is expected to be a fixed size, and it willhouse no more than 80 servers. By assigning a 192.168.8.0/25 CIDR, enoughroom is left for another contiguous CIDR, 192.168.8.128/25. Obviously, this isa more efficient way of managing the available IP space.Last but not least is the interconnection shown in Figure 1-4. This is therouter-to-router link between Router A and Router B. The interconnectionusually gets the least attention, but it exists everywhere in the multiplenetworks environment. Nonetheless, a CIDR block has to be assigned to it.Because there are always only two interface IP addresses involved plus thenetwork and broadcast address, giving an entire Class C address woulddefinitely be a waste. Typically, a /30 CIDR is used for this type of connection.Therefore, a CIDR block for the interconnection between Router A and RouterB can be 192.168.9.0/30. This yields two IP host addresses: one for Router Aand one for Router B.The complete subnet assignment for Example 1-1 and Figure 1-4 is providedinTable 1-3. Table 1-3. Completed Design of Subnets for Figure 1-4IP AssignmentThe next task requirement is that a CIDR block that can handle 800 networkdevices must be required to assign an IP address to each routed interface. Thisaddress will become the gateway IP address of the subnet. The gatewaydescribes the networking device that enables hosts in a LAN to connect to
networks (and hosts) outside the LAN. Figure 1-5 provides an example of thegateway. Every network device within its subnet (LAN) will use this IP addressas its gateway to communicate from its local subnet to devices on othersubnets. The gateway IP address is preselected and is distributed to a networkdevice by way of manual configuration or dynamic assignment. Figure 1-5. The gateway for a networkGatewayDescribes the networking device that enables hosts in a LAN to connect tonetworks (and hosts) outside the LAN.For LAN A in Example 1-1, the IP address 192.168.0.0 is already reserved asthe network address, and the IP address 192.168.0.255 is reserved as thebroadcast address. This leaves any IP address within the range 192.168.0.1–192.168.0.254 available for use for the gateway address. Choosing the gatewayIP address is not an exact science. Generally, the first IP address or the last IPaddress of the available range is chosen. Whatever convention is chosen, itshould apply to the rest of the subnets for the ease of management. Once thegateway IP address is chosen, this IP address is reserved and is not to be usedby any other devices in the subnet. Otherwise, an IP conflict will beintroduced. The following is an example of how the gateway IP addressescould be assigned to the LANs inExample 1-1.
1-3. VLAN NetworkThis section examines the function of using a switch in a VLAN within thecampus network. The terminology and steps for implementing VLANs will bepresented first. The second part examines basic Cisco switch configurationand provides an introduction to the commands needed for configuring theVLAN. The third part of Section 1-3 demonstrates the commands needed to setup a static VLAN. Next is a discussion on VLAN tagging using 802.1Q. Thesection concludes with a look at configuring an HP Procurve switch.LANs are not necessarily restricted in size. A LAN can have 20 computers, 200computers, or even more. Multiple LANs also can be interconnected toessentially create one large LAN. For example, the first floor of a buildingcould be set up as one LAN, the second floor as another LAN, and the thirdfloor another. The three LANs in the building can be interconnected intoessentially one large LAN using switches, with the switches interconnected, asshown in Figure 1-6.
Figure 1-6. Three floors of a building interconnected using switches to form one large LANIs it bad to interconnect LANs this way? As long as switches are being used tointerconnect the computers, the interconnected LANs have minimal impact onnetwork performance. This is true as long as there are not too manycomputers in the LAN. The number of computers in the LAN is an issue,because Layer 2 switches do not separate broadcast domains. This meansthat any broadcast sent out on the network (for example, the broadcastassociated with an ARP request) will be sent to all computers in the LAN.Excessive broadcasts are a problem, because each computer must process thebroadcast to determine whether it needs to respond; this essentially slowsdown the computer and the network.Broadcast DomainAny broadcast sent out on the network is seen by all hosts in this domain.A network with multiple LANs interconnected at the Layer 2 level is calleda flat network. A flat network is where the LANs share the same broadcastdomain. The use of a flat network should be avoided if possible for the simplereason that the network response time is greatly affected. Flat networks can beavoided by the use of virtual LANs (VLAN) or routers. Although both optionscan be used to separate broadcast domains, they differ in that the VLANoperates at the OSI Layer 2, while routers use Layer 3 networking toaccomplish the task. The topic of a virtual VLAN is discussed next.Flat NetworkA network where the LANs share the same broadcast domain.Virtual LAN (VLAN)Obviously, if the LANs are not connected, then each LAN is segregated only toa switch. The broadcast domain is contained to that switch; however, this doesnot scale in a practical network, and it is not cost effective because each LANrequires its own Layer 2 switches. This is where the concept of virtual LAN(VLAN) can help out. A VLAN is a way to have multiple LANs co-exist in thesame Layer 2 switch, but their traffic is segregated from each other. Eventhough they reside on the same physical switch, they behave as if they are ondifferent switches (hence, the term virtual). VLAN compatible switches cancommunicate to each other and extend the segregation of multiple LANsthroughout the entire switched network. A switch can be configured with aVLAN where a group of host computers and servers are configured as if theyare in the same LAN, even if they reside across routers in separate LANs. Each
VLAN has its own broadcast domain. Hence, traffic from one VLAN cannotpass to another VLAN. The advantage of using VLANs is the networkadministrator can group computers and servers in the same VLAN based onthe organizational group (such as Sales, Engineering) even if they are not onthe same physical segment—or even the same building.VLAN (Virtual LAN)A group of host computers and servers that are configured as if they are in thesame LAN, even if they reside across routers in separate LANs.There are three types of VLANs: port-based VLANs, tag-based VLANs,andprotocol-based VLANs. The port-based VLAN is one where the hostcomputers connected to specific ports on a switch are assigned to a specificVLAN. For example, assume the computers connected to switch ports 2, 3,and 4 are assigned to the Sales VLAN 2, while the computers connected toswitch ports 6, 7, and 8 are assigned to the Engineering VLAN 3, as shownin Figure 1-7. The switch will be configured as a port-based VLAN so that thegroups of ports [2,3,4] are assigned to the sales VLAN while ports [6,7,8]belong to the Engineering VLAN. The devices assigned to the same VLAN willshare broadcasts for that LAN; however, computers that are connected toports not assigned to the VLAN will not share the broadcasts. For example, thecomputers in VLAN 2 (Sales) share the same broadcast domain andcomputers in VLAN 3 (Engineering) share a different broadcast domain. Figure 1-7. An example of the grouping for port-based VLANsPort-Based VLANHost computers connected to specific ports on a switch are assigned to aspecific VLAN.Tagged-Based VLANUsed VLAN ID based on 802.1Q.Protocol-Based VLANConnection to ports is based on the protocol being used.
In tag-based VLANs, a tag is added to the Ethernet frames. This tag containstheVLAN ID that is used to identify that a frame belongs to a specific VLAN.The addition of the VLAN ID is based on the 802.1Q specification. The802.1Q standard defines a system of VLAN tagging for Ethernet frames. Anadvantage of an 802.1Q VLAN is that it helps contain broadcast and multicastdata traffic, which helps minimize data congestion and improve throughput.This specification also provides guidelines for a switch port to belong to morethan one VLAN. Additionally, the tag-based VLANs can help provide bettersecurity by logically isolating and grouping users.VLAN IDUsed to identify that a frame belongs to a specific VLAN.802.1QThis standard defines a system of VLAN tagging for Ethernet frames.In protocol-based VLANs, the data traffic is connected to specific ports basedon the type of protocol being used. The packet is dropped when it enters theswitch if the protocol doesn’t match any of the VLANs. For example, an IPnetwork could be set up for the Engineering VLAN on ports 6,7,8 and an IPXnetwork for the Sales VLAN on ports 2,3, and 4. The advantage of this is thedata traffic for the two networks is separated.There are two approaches for assigning VLAN membership:• Static VLAN: Basically a port-based VLAN. The assignments are createdwhen ports are assigned to a specific VLAN.• Dynamic VLAN: Ports are assigned to a VLAN based on either thecomputer’s MAC address or the username of the client logged onto thecomputer. This means that the system has been previously configured with theVLAN assignments for the computer or the username. The advantage of this isthe username and/or the computer can move to a different location, but VLANmembership will be retained.Static VLANBasically, a port-based VLAN.Dynamic VLANPorts are assigned to a VLAN based on either the computer’s MAC address orthe username of the client logged onto the computer.VLAN ConfigurationThis section demonstrates the steps for configuring a static VLAN. In thisexample, the ports for VLAN 2 (Sales) and VLAN 3 (Engineering) will be
defined. This requires that VLAN memberships be defined for the requiredports. The steps and the commands will be demonstrated.The show vlan command can be used to verify what ports have been definedfor the switch. By default, all ports are assigned to VLAN 1. An example usingtheshow vlan command is provided next. Click here to view code imageSwitchA# show vlanVLAN Name Status Ports---- -------------------------- --------- -----------------------------1 default active Fa0/1, Fa0/2,Fa0/3, Fa0/4 Fa0/5,Fa0/6, Fa0/7, Fa0/8 Fa0/9,Fa0/10show vlanUsed to verify what ports have been defined for the switch.This shows that all the FastEthernet interfaces on the switch are currentlyassigned to VLAN 1, which is a default VLAN. In the next step, two additionalVLANs will be created for both Sales and Engineering. The two new VLANswill have the VLAN ID of 2 and 3 respectively, and each VLAN will be assigneda name associated to it. This is accomplished by modifying the VLAN databaseusing thevlan database command, as shown in the next steps.vlan databaseThe command used on older Cisco switches to enter the VLAN database. Click here to view code imageSwitchA#vlan databaseSwitchA(vlan)#vlan 2 name SalesVLAN 2 modified: Name: SalesSwitchA(vlan)#vlan 3 name EngineeringVLAN 3 modified: Name: EngineeringOn newer Cisco switches, users will get the following message that thecommandvlan database is being deprecated: Click here to view code image% Warning: It is recommended to configure VLAN from config mode, as VLAN database mode is being deprecated. Please consult user documentation for configuring VTP/VLAN in config mode.Cisco has moved away from the VLAN database-style command to an IOSglobal command. Similarly to other IOS global commands, the switch must bein the configuration mode (config)#. However, the concept remains the same
that a VLAN must be created for it to be activated and ready for use. The stepsfor creating the VLAN on newer Cisco switches are as follows: Click here to view code imageSwitchA# conf tSwitchA(config)#vlan 2SwitchA(config-vlan)#name SalesSwitchA(config-vlan)#vlan 3SwitchA(config-vlan)#name EngineeringSwitchA(config-vlan)#exitSwitchA(config)#exitTo start configuring a VLAN, one must specify which VLAN needs to beconfigured using the vlan [vlan_id] command. If the specific VLAN does notexist, this command will create the VLAN as well. As shown in the precedingexample, the command vlan 2 is entered to configure vlan 2 and then thecommand name Sales is entered to configure the name associated to theVLAN. The similar steps are done for VLAN 3 with the name Engineering.vlan [vlan_id]The IOS global command used to create VLAN ID.The rest of the VLAN commands are almost identical in the older switches andnewer switches. The next step is used to verify that the new VLANs have beencreated using the show vlan command: Click here to view code imageSwitch#show vlanVLAN Name Status Ports---- -------------------------- --------- -----------------------------1 default active Fa0/1, Fa0/2, Fa0/3,Fa0/4 Fa0/5, Fa0/6,Fa0/7, Fa0/8 Fa0/9, Fa0/102 Sales active3 Engineering activeThis shows that both the Sales and Engineering VLANs have been created. Inthe next steps, ports will be assigned to the newly created VLANs. Thisrequires that the configuration mode be entered and each FastEthernetinterface (port) must be assigned to the proper VLAN using the twocommands switchport mode access and switchport access vlan vlan-id.An example is presented for FastEthernet interface 0/2 being assigned toVLAN 2 on a Cisco switch: Click here to view code imageSwitchA#conf tEnter configuration commands, one per line. End with CNTL/Z.SwitchA(config)#int fa 0/2SwitchA(config-if)#switchport mode accessSwitchA(config-if)#switchport access vlan 2SwitchA(config-if)#end
The next step is used to verify that FastEthernet 0/2 has been assigned to theSales VLAN (VLAN2). This can be verified using the show vlanbrief command, as shown. This command only displays the interfacesassigned to each VLAN: Click here to view code imageSwitchA#sh vlan briefVLAN Name Status Ports---- ----------------------------- --------- ------------------------1 default active Fa0/1, Fa0/3, Fa0/4,Fa0/5 Fa0/6, Fa0/7,Fa0/8, Fa0/9 Fa0/102 Sales active Fa0/2The next steps are to assign ports 3 and 4 to the Sales VLAN (VLAN 2) andports 6,7,8 to Engineering (VLAN 3). Once this is completed, the portassignments can be verified using the show vlan command, as shown: Click here to view code imageSwitchA#show vlanVLAN Name Status Ports---- ---------------------------- --------- -------------------------1 default active Fa0/1, Fa0/5,Fa0/9, Fa0/102 Sales active Fa0/2, Fa0/3,Fa0/43 Engineering active Fa0/6, Fa0/7, Fa0/8You can look specifically at the assignments for only one of the VLANs byentering the command show vlan name vlan-name, where vlan-name isthe name assigned to the VLAN. Note that the name is case-sensitive. You canalso use the number of the VLAN instead of using the command show vlanid vlan-id. Examples of both are presented:show vlan name vlannameThe command to look specifically at only one of the VLANs. Click here to view code imageSwitchA#show vlan name EngineeringVLAN Name Status Ports---- -------------------------------- --------- ---------------------3 Engineering active Fa0/6, Fa0/7,Fa0/8Switch#show vlan id 3VLAN Name Status Ports
---- -------------------------------- --------- ---------------------3 Engineering active Fa0/6, Fa0/7,Fa0/8On Layer 2 switches, an IP address can be assigned to a VLAN interface. Thismerely assigns an IP address to a switch, so that a switch can communicatewith other network devices on the same VLAN and vice-versa. The IP VLANinterface does not perform any routing functions when running as a layer 2switch. As a matter of fact, the IP VLAN interface is not required in order for aswitch to start forwarding packets and perform its other Layer 2 functions. Bydefault, theinterface VLAN 1 is automatically created. The followingcommand sequence demonstrates how to assign the IP address to the VLANinterface:interface VLAN 1The default vlan for the switch. Click here to view code imageSwitchA(config)# interface VLAN 1SwitchA(config-if)# ip address 192.168.1.1 255.255.255.0SwitchA(config-if)# no shutdownNote that the IP address is being set for VLAN 1. The interface for the switch isalso enabled at this same point using the no shutdown command, as shown.In order for the interface VLAN to be up, at least one switch port in the VLANmust be up or have a physical link. The status of a switch port can be verifiedwith the command show interface or, better yet, with the command showinterface status. Although the command show interface shows detailedinformation of individual interface one at a time, the command showinterface statusdisplays the status of all the switch ports including theirspeed, duplex, and VLAN, as shown. This gives a quick and precise look of theport status of a switch where port density is high.show interface statusUsed to verify the status of a switchport. Click here to view code imageSwitchA#show interface statusPort Name Status Vlan Duplex Speed TypeFa0/1 connected 1 a-full a-10010/100BaseTXFa0/2 connected 2 a-full a-10010/100BaseTXFa0/3 connected 2 a-full a-10010/100BaseTXFa0/4 connected 2 a-full a-10010/100BaseTXFa0/5 connected 1 a-full a-100
10/100BaseTXFa0/6 connected 3 a-full a-10010/100BaseTXFa0/7 connected 3 a-full a-10010/100BaseTXFa0/8 connected 3 a-full a-10010/100BaseTXFa0/9 connected 1 a-full a-10010/100BaseTXFa0/10 connected 1 a-full a-10010/100BaseTXThe overall configuration of the switch can be viewed using the showrunning-config (sh run) command, as shown. (Only a part of theconfiguration is displayed.) Click here to view code imageSwitch#sh run - -Building configuration...Current configuration : 1411 bytes!version 12.1no service padservice timestamps debug uptimeservice timestamps log uptimeno service password-encryption!hostname Switch!ip subnet-zero!spanning-tree mode pvstno spanning-tree optimize bpdu transmissionspanning-tree extend system-id!interface FastEthernet0/1!- interface FastEthernet0/2 switchport access vlan 2 switchport mode access . . . . . . . .interface FastEthernet0/5!interface FastEthernet0/6 switchport access vlan 3 switchport mode access!interface FastEthernet0/9!interface FastEthernet0/10!!interface Vlan1 ip address 192.168.1.1 255.255.255.0
no ip route-cache!ip http server!line con 0line vty 0 15 loginendThe running-configuration for the switch shows that the FastEthernetinterfaces have been assigned to the proper VLANs. Additionally, this showsthat an IP address has been assigned to the default interface VLAN1.This portion of the text has demonstrated the steps for creating a static VLAN.Both Sales and Engineering VLANs were created, and specific ports on theswitch were assigned to the respective VLANs. Unassigned ports remained aspart of the default VLAN 1.VLAN TaggingThis section explores the concept of VLAN tagging (802.1Q) and demonstratesthe steps required for this configuration. The concept of VLAN tagging can beexplained using the example network shown in Figure 1-8. In this network, theSales team is spread out in two different buildings. Therefore, the Sales VLANnetwork must be available in both buildings. Each building has its ownnetwork switch, and both switches are connected via one physical link. Figure 1-8. An example of a scenario with two VLANS spread across two buildingsIn a scenario like this, not only is it necessary to have the same Sales VLANrunning on both building switches, it is also important to have members of thesame VLAN being able to communicate with each other across buildings andto adhere to the same VLAN restrictions. To accomplish this, a techniquecalled VLAN tagging is used. VLAN tagging is a technique deployed on aswitch interface to carry Ethernet frames of multiple VLANs. The interfacemust connect to another switch port, router port, or network device thatunderstands VLAN tagging, and both sides must agree on the VLAN taggingprotocol.Trunk PortA switch interface or port configured to carry multiple VLANs.
Inter-Switch Link (ISL)The Cisco proprietary VLAN tagging protocol.The standard protocol for VLAN tagging is IEEE 802.1Q. This standardprotocol is widely supported by every switch manufacturer, as well as Cisco. Aswitch interface or port configured to carry traffic for multiple VLANs is oftenreferred to as a trunk port. The term was made famous by Cisco, and it isused explicitly as the VLAN tagging command in Cisco switches. Note thatCisco has its own proprietary VLAN tagging protocol called Inter-SwitchLink (ISL). The big difference between ISL and 802.1Q is how the frame istreated. In ISL, every Ethernet frame is encapsulated within a 26-Byte headercontaining the VLAN ID and a 4 Byte CRC at the end. This makes the size ofan ISL frame bigger than an 802.1Q frame, as discussed next.To accomplish the VLAN tagging of the Ethernet frames, IEEE 802.1Q simplyinserts additional data to the Ethernet frame header, as shown in Figure 1-9.An 802.1Q tag is a 4-Byte tag field that is inserted between the Source Addressfield and the Ethernet Type/Length field. By inserting an additional 4-Bytefield, the Ethernet frame size is increased. Its minimum frame size is nowincreased from 64 Bytes to 68 Bytes, and its maximum frame size is nowincreased from 1,518 Bytes to 1,522 Bytes. Figure 1-9 also provides a detailedcalculation of the Ethernet frame size. Because of the additional tag field andthe increased frame size, it is important that both sides of the link becompatible. Otherwise, the tagged Ethernet frames will not be understoodand, therefore, the frames will be dropped by a non-802.1Q-compliantinterface.
Figure 1-9. Typical Ethernet frame versus Ethernet frame with 802.1Q tag802.1Q ConfigurationThis section demonstrates the steps for configuring 802.1Q VLAN tagging.The 802.1Q VLAN tagging is configured at the switch interface thatinterconnects to another network switch. In this case, interface FastEthernet0/1 of Switch A is selected as a 802.1Q VLAN tagging port or a trunk port. Thefollowing demonstrates how to configure an interface as a trunk port on aCisco switch.First, the interface is assigned as a trunk port by the command switchportmode trunk. This essentially turns on trunking. The next step is to define thetagging protocol, which is 802.1Q, in this case. The command switchporttrunk encapsulation dot1q is used. If ISL is used, the command wouldbeswitchport trunk encapsulation isl. The next command, switchporttrunk allowed vlan vlan-id, is optional, but it is useful in limiting VLANsthat can be carried across the link.
switchport mode trunkTurns on trunking.switchport trunk encapsulation dot1qThis command defines that 802.1Q tagging protocol is being used.switchport trunk encapsulation islThis command defines that the tagging protocol is ISL.switchport trunk allowed vlan vlan-idThis command is used to limit the VLANs that can be carried across the link. Click here to view code imageSwitchA#conf tEnter configuration commands, one per line. End with CNTL/Z.SwitchA(config)#int fa 0/1SwitchA(config-if)#switchport mode trunkSwitchA(config-if)#switchport trunk encapsulation dot1qSwitchA(config-if)#switchport trunk allowed vlan 1,2SwitchA(config-if)#endBy default, all configured VLANs are allowed across the trunk port. In orderfor VLAN tagging to work properly, it is important to configure the samecommands on SwitchB’s trunk port. To verify the 802.1Q configuration, thecommand show interfaces trunk can be used:show interfaces trunkThis command is used to verify the 802.1Q configuration. Click here to view code imageSwitchA#sh interfaces trunkPort Mode Encapsulation Status Native vlanFa0/1 on 802.1q trunking 1Port Vlans allowed on trunkFa0/1 1,2Port Vlans allowed and active in management domainFa0/1 1,2Port Vlans in spanning tree forwarding state and not prunedFa0/1 1,2Networking Challenge: Static VLAN ConfigurationUse the Net-Challenge Simulator Software included with the text’s companionCD-ROM to demonstrate that you can perform basic switch and static VLANconfiguration and set up a trunk connection. Place the CD-ROM in yourcomputer’s drive. Open the Net-Challenge folder, andclick NetChallengeV3-2.exe. After the software is running, click theSelectChallenge button. This opens a Select Challenge drop-down menu. Select
the Chapter 1 - Static VLAN Configurationchallenge to open a checkboxthat can be used to verify that you have completed all the tasks. Do thefollowing:1. Enter the privileged EXEC mode on the switch (password: Chile).2. Enter the switch’s configuration mode: Router(config).3. Set the hostname of the switch to switch-A.4. Configure the IP address for VLAN 1 interface with the following:IP address: 10.10.20.250Subnet mask: 255.255.255.05. Enable the VLAN 1 interface.6. Use the command to display the current VLAN settings for the switch.7. Issue the command that lets you modify the VLAN database.8. Create a VLAN 2 named Sales.9. Verify that a new Sales VLAN has been created.10. Issue the command to enter the fa0/2 interface configuration mode.11. Enter the sequence of commands that are used to assign interface fa0/2 tothe Sales VLAN.12. Enter the command that enables you to display the interface assigned toeach VLAN.13. Enter the command that enables you to view specifically the assignmentsfor the Sales VLAN.14. Issue the command that allows you to view the switch’s running-configuration.15. Issue the command to turn on trunking for SwitchA.16. Issue the command to set trunk encapsulation to 802.1Q.17. Issue the command that enables VLAN 1 and VLAN 2 to be carried acrossthe link.Configuring the HP Procurve SwitchThis should not come as a surprise to learn that many switch manufacturersfollow a similar configuration path as the Cisco switches. A similar Cisco-styled command-line interface (CLI) is deployed by those manufacturers aswell. The following is an example of how to configure an HP Procurve switch.The first step is to enter the configuration mode using thecommand configure. Next, the VLAN # is entered using the vlan2 command. Finally, the VLAN is assigned a name from the (vlan-2) promptusing the command name-Sales: Click here to view code imageSwitchHP# configureSwitchHP(config)#vlan 2SwitchHP(vlan-2)#name Sales
The command show vlan also exists on the HP switches, but the outputresult is different than the one produced from Cisco switches. The HP’s showvlancommand does not provide ports with VLAN membership, while theCisco command does: Click here to view code image SwitchHP# show vlanStatus and Counters - VLAN Information Maximum VLANs to support : 8 Primary VLAN : DEFAULT_VLAN Management VLAN : 802.1Q VLAN ID Name Status Voice Jumbo -------------- ------------ ------------ ----- ----- 1 DEFAULT_VLAN Port-based No No 2 Sales Port-based No NoOn a Cisco switch, the VLAN membership is configured at the interface level.On an HP switch, it is configured at the VLAN level, where each VLANcontains its port members. This example shows how a VLAN membership isassigned on an HP switch: Click here to view code imageSwitchHP# configureSwitchHP(config)#vlan 2SwitchHP(vlan-2)#untagged 48In VLAN 2, port 48 is configured as an untagged member. This means that theport is not a tagged VLAN port. It is essentially just a port-based VLAN. It wasmentioned earlier that the HP’s command show vlan does not give muchdetail. To get more VLAN details, one must specify the VLAN ID. The showvlan 2command can be used to verify that port 48 has been assigned to theSales VLAN (VLAN2): Click here to view code imageSwitchHP# show vlan 2 Status and Counters - VLAN Information - Ports - VLAN 2 802.1Q VLAN ID : 2 Name : Sales Status : Port-based Voice : No Jumbo : No Port Information Mode Unknown VLAN Status ------------------- -------------------- ---------- --------- 48 Untagged Learn UpOn HP switches and other switch manufacturers, the command syntax forenabling a port to carry 802.1Q tagged frames is basically the same. On HPswitches, there is not a trunk command. The step is to simply assign taggingability to the switch port by issuing thecommand tagged port_number. Because this is a non-Cisco switch, 802.1Q isthe only VLAN tagging protocol that can be used. The following command
sequence demonstrates how to configure an interface port 24 on an HP switchas a 802.1Q VLAN tagging port: Click here to view code imageSwitchHP# confSwitchHP(config)# vlan 1SwitchHP(vlan-1)# tagged 24SwitchHP(vlan-1)# exitSwitchHP(config)# vlan 2SwitchHP(vlan-2)# tagged 24SwitchHP(vlan-2)# exitUnlike Cisco switches where an 802.1Q is configured at the interface level, thetagging configuration is done at the VLAN level on HP switches. Port 24 isdesignated as tagged port for both VLAN 1 and VLAN 2, which enables it tocarry VLAN 1 and VLAN 2 frames. Generally, untagged ports belong to onespecific VLAN, while tagged ports can belong to one or more VLANs.1-4. Routed NetworkThis section examines the Layer 3 network and how data is routed in thenetwork. This section also introduces another Layer 3 device, the multilayerswitch. You need to understand the advantages and disadvantages of thisdevice. This section also introduces interVLAN configuration, which enablesVLANs to communicate across networks. The section concludes with a look atboth serial and ATM configurations. Some network engineers will argue thatthe serial and ATM technologies are a dying technology and are nowconsidered obsolete. However, being obsolete does not mean they arenonexistent. These technologies are still being used throughout the world, andit is still an important topic.RouterThe router is a powerful networking device used to interconnect LANs. Therouter is a Layer 3 device in the OSI model, which means the router usesthenetwork address (Layer 3 addressing) to make routing decisionsregarding forwarding data packets. In the OSI model, the Layer 3, or network,layer responsibilities include handling of the network address. The networkaddress is also called a logical address, rather than being a physical address(such as the MAC address, which is embedded into the network interface card[NIC]). Thelogical address describes the IP address location of the networkand the address location of the host in the network.Network AddressAnother name for the Layer 3 address.Logical AddressThis describes the IP address location of the network and the address locationof the host in the network.
Essentially, the router is configured to know how to route data packetsentering or exiting the LAN. This differs from the bridge and the Layer 2switch, which use the Ethernet address for making decisions regardingforwarding data packets and only know how to forward data to hostsphysically connected to their ports.Routers are used to interconnect LANs in a campus network. Routers can beused to interconnect networks that use the same protocol (for example,Ethernet), or they can be used to interconnect LANs that are using differentLayer 2 technologies, such as an Ethernet, ATM, T1, and so on. Routers alsomake it possible to interconnect to LANs around the country and the worldand interconnect to many different networking protocols. The router portsarebidirectional, meaning that data can enter and exit the same router port.Often, the router ports are called the router interface, which is the physicalconnection where the router connects to the network.Router InterfaceThe physical connection where the router connects to the network.The network provided in Figure 1-10 is an example of a simple three-routercampus network. This configuration enables data packets to be sent andreceived from any host on the network after the routers in the network havebeen properly configured. For example, computer A1 in LAN A could besending data to computer D1 in LAN D. This requires that the IP address forcomputer D1 is known by the user sending the data from computer A1. Thedata from computer A1 will first travel to the switch where the data is passedto Router A via the FA0/0 FastEthernet data port. Router A will examine thenetwork address of the data packet and use configured routing instructionsstored in the router’s routing tables to decide where to forward the data.Router A determines that an available path to Router C is via the FA0/2FastEthernet port connection. The data is then sent directly to Router C.Router C determines that the data packet should be forwarded to its FA0/0port to reach computer D1 in LAN D. The data is then sent to D1. Alternatively,Router A could have sent the data to Router C through Router B via Router A’sFA0/1 FastEthernet port.
Figure 1-10. The three-router campus LANDelivery of the information over the network was made possible by the use ofan IP address and routing table. Routing tables keep track of the routes usedfor forwarding data to its destination. RouterA used its routing table todetermine a network data path so computer A1’s data could reach computerD1 in LAN D. After the data packet arrived on Router C, an ARP request isissued by Router C to determine the MAC address of computer D1. The MACaddress is then used for final delivery of the data to computer D1.Routing TableKeeps track of the routes to use for forwarding data to its destination.If Router A determines that the network path to Router C is down, Router Acan route the data packet to Router C through Router B. After Router Breceives the data packet from Router A, it uses its routing tables to determinewhere to forward the data packet. Router B determines that the data needs tobe sent to Router C. Router B will then use its FA0/3 FastEthernet port toforward the data to Router C.
Gateway AddressAs previously discussed, the term gateway is used to describe the address ofthe networking device that enables the hosts in a LAN to connect to networksand hosts outside the LAN. For example, the gateway address for all hosts inLAN A will be 10.10.20.250. This address is configured on the host computer,as shown in Figure 1-11. Any IP packets with a destination outside the LAN Anetwork will be sent to this gateway address. Note that the destinationnetwork is determined by the subnet mask. In this case, the subnet mask is255.255.255.0. Figure 1-11. Network settings configuration for the default gatewayNetwork SegmentsThe network segment defines the networking link between two LANs. There isa segment associated with each connection of an internetworking device (forexample, router-hub, router-switch, router-router). For example, the IPaddress for the network segment connecting LAN A to the router is 10.10.20.0.All hosts connected to this segment must contain a 10.10.20.x, because asubnet mask of 255.255.255.0 is being used. Subnet masking is fully explainedin Network Essentials Chapter 6, ―TCP/IP.‖
Routers use the information about the network segments to determine whereto forward data packets. For example, referring to Figure 1-10, the networksegments that connect to Router A include10.10.20.010.10.200.010.10.100.0The segment is sometimes called the subnet or NET. These terms areassociated with a network segment address, such as 10.10.20.0. In this case,the network is called the 10.10.20.0 NET. All hosts in the 10.10.20.0 NET willhave a 10.10.20.x IP address. The network addresses are used whenconfiguring the routers and defining which networks are connected to therouter.Subnet, NETOther terms for the segment.According to Figure 1-11, all the computers in LAN A must have a 10.10.20.xaddress. This is defined by the 255.255.255.0 subnet mask. For example,computer A1 in LAN A will have the assigned IP address of 10.10.20.1 and agateway address of 10.10.20.250. The computers in LAN B (see Figure 1-10)are located in the 10.10.10.0 network. This means that all the computers inthis network must contain a 10.10.10.x IP address. In this case, the x part ofthe IP address is assigned for each host. The gateway address for the hosts inLAN B is 10.10.10.250. Notice that the routers are all using the same .250gateway address. Remember, any valid IP address can be used for the gatewayaddress, but it is a good design procedure to use the same number for numberfor all routers. In this case, .250 is being used. In other cases, it could be .1 or.254.The subnet mask is used to determine whether the data is to stay in the LANor is to be forwarded to the default gateway provided by the router. The routeruses its subnet mask to determine the destination network address. Thedestination network address is checked with the router’s routing table to selectthe best route to the destination. The data is then forwarded to the next router,which is the next hop address. The next router examines the data packet,determines the destination network address, checks its routing table, and thenforwards the data to the next hop. If the destination network is directlyconnected to the router, it issues an ARP request to determine the MACaddress of the destination host. Final delivery is then accomplished byforwarding the data using the destination host computer’s MAC address.Routing of the data through the networks is at Layer 3, and the final deliveryof data in the network is at Layer 2.
Multilayer SwitchSo far, the topic of network switches revolves around their Layer 2functionalities. Today, the scope of operations has changed for switches.Newer switch technologies are available to help further improve theperformance of computer networks. This new development started with Layer3 switches and now there are multilayer switches. The term used to describethese switches that can operate above the OSI Layer 2 is multilayerswitches (MLS). An example is a Layer 3 switch. Layer 3 switches still workat Layer 2, but additionally work at the network layer (Layer 3) of the OSImodel and use IP addressing for making decisions to route a data packet in thebest direction. The major difference is that the packet switching in basicrouters is handled by a programmed microprocessor. The multilayer switchuses application specific integrated circuits (ASIC) hardware to handle thepacket switching. The advantage of using hardware to handle the packetswitching is a significant reduction in processing time (software versushardware). In fact, the processing time of multilayer switches can be as fast asthe input data rate. This is called wire speed routing, where the datapackets are processed as fast as they are arriving. Multilayer switches can alsowork at the upper layers of the OSI model. An example is a Layer 4 switch thatprocesses data packets at the transport layer of the OSI model.Multilayer Switch (MLS)Operates at Layer 2, but functions at the higher layers.Wire Speed RoutingData packets are processed as fast as they arrive.Through this evolution, the line between routers and multilayer switches isgetting more and more blurry. Routers were once considered the moreintelligent device, but this is no longer true. With new developments, themultilayer switches can do almost everything the routers can. Moreimportantly, most of the Layer 3 switch configuration commands are almostidentical to the ones used on the routers. Routers tend to be more expensivewhen it comes to cost per port. Therefore, most of the traditional designs havea router connecting to a switch or switches to provide more port density. Thiscan be expensive depending on the size of the network. So, there has been ashift toward deploying multilayer switches in the network LAN environmentin place of routers. In this case, the routers and switches in Figure 1-10 thencould all be replaced with multilayer switches. This also means there will beless network equipment to maintain, which reduces the maintenance cost andmakes this a more cost-effective solution. With its greater port density, amultilayer switch can serve more clients than a router could. However, there isa common drawback for most multilayer switches: These devices only support
Ethernet. Other Layer 2 technologies, such as ATM, DSL,T1, still depend onrouters for making this connection.Layer 3 Routed NetworksAs discussed previously, the hosts are interconnected with a switch or hub.This allows data to be exchanged within the LAN; however, data cannot berouted to other networks. Also, the broadcast domain of one LAN is notisolated from another LAN’s broadcast domain. The solution for breaking upthe broadcast domains and providing network routing is to incorporaterouting hardware into the network design to create a routed network. Arouted network uses Layer 3 addressing for selecting routes to forward datapackets, so a better name for this network is a Layer 3 network.Routed NetworkUses Layer 3 addressing for selecting routes to forward data packets.Layer 3 NetworkAnother name for a routed network.In Layer 3 networks, routers and multilayer switches are used to interconnectthe networks and LANs, isolating broadcast domains and enabling hosts fromdifferent LANs and networks to exchange data. Data packet delivery isachieved by handing off data to adjacent routers until the packet reaches itsfinal destination. This typically involves passing data packets through manyrouters and many networks. An example of a Layer 3 network is shownin Figure 1-10. This example has four LANs interconnected using threerouters. The IP address for each networking device is listed.The physical layer interface on the router provides a way to connect the routerto other networking devices on the network. For example, the FastEthernetports on the router are used to connect to other FastEthernet ports on otherrouters or switches. Gigabit and 10-gigabit Ethernet ports are also available onrouters to connect to other high-speed Ethernet ports (the sample networkshown in Figure 1-10 includes only FastEthernet ports). Routers also containother types of interfaces, such as serial interfaces and Synchronous OpticalNetwork (SONET) interfaces. These interfaces were widely used tointerconnect the router and the network to other wide-area networks (WAN).For example, connection to WANs requires the use of a serial interface orSONET interface to connect to a communications carrier, such as Sprint,AT&T, Century Link, and so on. The data speeds for the serial communicationports on routers can vary from slow (56 kbps) up to high-speed DS3 data rates(47+ Mbps), and the SONET could range from OC3 (155 Mbps), OC12 (622Mbps), or even OC192 (9953 Mbps).
Synchronous Optical Network (SONET)Used to interconnect the router and the network to other WANs.WANWide-area network.Routed Port ConfigurationRouters can have Ethernet (10 Mbps), Fast Ethernet (100 Mbps), GigabitEthernet (1,000 Mbps), and 10 gigabit (10 GB), Serial, and ATM interfaces.These routers can have multiple interfaces, and the steps for configuring eachinterface are basically the same. Each interface is assigned a number. Forexample, a router could have three FastEthernet interfaces identified asFastEthernet 0/0FastEthernet 0/1FastEthernet 0/2The notation 0/0 indicates the [interface-card-slot/port].On Cisco’s routers, a routed port can be configured simply by assigning an IPaddress to the interface. Once an IP address and its subnet mask are assignedto the interface and the interface is enabled, a Layer 3 network is created. Theinterface IP address becomes the gateway for that network. To program theinterface, the router must be in the configuration mode. The followingdemonstrates how to configure a router’s FastEthernet 0/0 port (FastEthernet0/0, also listed as fa0/0 and FA0/0) as a routed interface. Click here to view code imageRouter(config)# int fa0/0Router(config-if)# ip address 10.10.20.250 255.255.255.0Router(config-if)#no shut2w0d: %LINEPROTO-5-UPDOWN: Line protocol on Interface FastEthernet0/0,changed state to upNotice that the router prompts you that the line protocol on interfaceFastEthernet 0/0 changed state to up. These log messages are alwaysdisplayed when connecting via the console port. However, they are suppressedwhen it is a remote terminal session, like Telnet or SSH. To display logmessages on the remote terminal, issue the command terminalmonitor or term mon at the router prompt:terminal monitor (term mon)Displays log messages on the remote terminal.Router# term monThe log messages can be useful when bringing up a new connection.Sometimes, they can be annoying if the router is logging too many events. Todisable the logging to the terminal, the command is terminal no
monitor or term no mon. One would think the command syntax wouldstart with no, like typical Cisco command, but it is not so in this case:terminal no monitor (term no mon)Disables the logging to the terminal.Router# term no monThe command show ip interface brief (sh ip int brief) entered at theenable prompt (Router#) can be used to verify the status of the routerinterfaces. The following is an example: Click here to view code imageRouter# sh ip int briefInterface IP-Address OK? Method Status ProtocolFastEthernet0/0 10.10.20.250 YES manual up upFastEthernet0/1 unassigned YES manual administratively downdownFastEthernet0/2 unassigned YES manual administratively downdownshow ip interface brief (sh ip int brief)Verifies the status of the router interfaces.The output shows that the interface FastEthernet0/0 was configured with theIP address and its status is up. Because the FastEthernet0/1 andFastEthernet0/2 were not yet configured, their IP addresses are shown asunassigned and their interfaces are still administratively shut down.Also, a routed port can be assigned to a multilayer switch. This configurationis simple and the same as configuring a router port. The first step is to convertthe native switch port to a router port. This is accomplished by issuing thecommandno switchport on the desired switch interface. Then, the IPaddress and other configuration can be applied to the interface just like atypical router port: Click here to view code imageSwitchA(config)# interface FastEthernet0/1SwitchA(config-if)# no switchportSwitchA(config-if)# ip address 192.168.1.1 255.255.255.0SwitchA(config-if)# no shutdownno switchportConverts the native switch port to a router port.One concept that is worth exploring is secondary IP address. The primaryaddress is the IP address that is assigned to the interface. The secondary IPaddress is a way to support multiple IP addresses per router interface. Hence,it allows multiple Layer 3 networks to reside on the same physical link.
Secondary IP addresses can be useful when you want to add more networkswithout having to disturb the existing network or to use it as a transitionalnetwork for network migration. Some people might just want to run multiplelogical subnets on one physical subnet. To add a secondary IP address to theinterface, the command isip address [ip_address][subnet_mask] secondary. The keyword secondaryis used to specify thesecondary IP address. The secondary IP address configuration is as follows: Click here to view code imageRouter(config)# interface FastEthernet0/0Router(config-if)# ip address 10.10.20.250 255.255.255.0Router(config-if)# ip address 172.16.1.1 255.255.255.0 secondarySecondary IP AddressAllows multiple Layer 3 networks to reside on the same physical link.In order to configure the secondary IP address, the primary IP address mustexist first. There can be as many secondary IP addresses as needed. Thesecondary IP address cannot be verified with the show int or show ip intbrief command. The results will only display the primary IP addressinformation.InterVLAN Routing ConfigurationAs previously discussed in Section 1-3, ―VLAN Network,‖ each VLAN is its ownbroadcast domain. It cannot forward traffic across its VLAN boundaries.However, it is almost impractical in today’s applications for a VLAN not to beable to communicate beyond itself. To enable communications amongVLANs,InterVLAN routing is required.InterVLAN routingEnables communications among VLANs.router on a stickEliminates connecting a link from each VLAN to a router port by utilizing atrunk or 802.1Q port.The most logical solution to route traffic between different VLANs is tointroduce or create a Layer 3 routed network between them. One traditionalway is to connect each VLAN to a router interface. Then, each router interfaceis configured as a different Layer 3 network. This enables VLANs tocommunicate and pass traffic via the Layer 3 IP network. For a few VLANs,this does not present an issue, but for a large number of VLANs, this couldcreate some issues. This means that every VLAN will require a physicalconnection to a router port. Router ports are expensive, and this design can becostly as the number of VLANs increases and more physical links are required.
A more common and popular design is to implement a router on a stick.The router on a stick design eliminates connecting a link from each VLAN to arouter port by utilizing a trunk or 802.1Q port. A single trunk port isconnected to a router, and it passes the tagged VLAN traffic to the router, asdepicted in Figure 1-12. Figure 1-12. Router on a stick topologyThis design requires that the router must be configured to accept the taggedVLANs. A Layer 3 network is then assigned to each VLAN coming to therouter. To accomplish this, subinterfaces are created under the routerinterface at which the switch trunk port is terminated. The subinterface is avirtual interface, and its notation is a dot followed by the subinterface number.In the example provided, the subinterfaces are listed as FastEthernet0/0.1,0.2, and 0.3. For the ease of programming, it is recommended to keep thesubinterface number the same as the VLAN ID. Recall that the default VLANis 1, the Sales VLAN is 2, and the Engineering VLAN is 3. The next step is todefine the VLAN tagging encapsulation. In this case, it is dot1q, whichessentially is 802.1Q. With the encapsulation, the appropriate VLAN ID isspecified. Next, the IP address is assigned creating a routed Layer 3 networkfor a VLAN. The following example demonstrates how to configure a Ciscorouter for a 802.1Q interVLAN routing: Click here to view code imageRouter(config)#interface FastEthernet0/0Router(config-if)#no ip addressRouter(config-if)#interface FastEthernet0/0.1Router(config-if)#description Default VLANRouter(config-subif)#encapsulation dot1Q 1Router(config-subif)#ip address 172.16.10.1 255.255.255.0Router(config-subif)#interface FastEthernet0/0.2Router(config-subif)#description Sales VLANRouter(config-subif)#encapsulation dot1Q 2