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: ...
Chapter 7: Advanced Switching Concepts    Quick Answer Key    Answers and ExplanationsChapter 8: Subnetting, VLSM, and IPv...
This chapter covers the following CCNA objectives that fall under the contentarea, Describe how a network works:         D...
Quick Answer: 16Detailed Answer: 173. Which of the following is a security concern when configuring a device   using Telne...
6. You are preparing to discuss the foundations of network communication   with a junior administrator at your company. Ho...
2. B. 1.544 MBps      3. C. 1.544 Gbps      4. D. 1.544 GBpsQuick Answer: 16Detailed Answer: 1810. Routing decisions are m...
from one device to another        2. B. To control broadcast and multicast traffic from flooding through multiple         ...
5. E. The IP address of SwitchB      6. F. The IP address of ServerBQuick Answer: 16Detailed Answer: 1916. Refer to Figure...
18. Which of the following are valid fields in a TCP header? (Choose four.)      1. A. Sequence number      2. B. Source I...
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...
22. Refer to Figure 1.4. HostA just transmitted a certain amount of data to    HostB. What does HostBs response indicate?F...
1.   A. ______ Segments       2.   B. ______ Frames       3.   C. ______ Bits       4.   D. ______ PacketsQuick Answer: 16...
Figure 1.5. Command prompt output.   1. A. All host and server connections in the network should have speed and duplex    ...
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 ...
Table of ContentsIntroduction
About This Book How to Use This Book How This Book Is Organized   Book I: Networking Basics   Book II: Building a Network ...
Fast Ethernet   Gigabit Ethernet The TCP/IP Protocol Suite   IP   TCP   UDP Other Protocols Worth Knowing AboutChapter 3: ...
Windows Vista   Older Windows versionsBook IIChapter 1: Planning a Network Making a Network Plan Being Purposeful Taking S...
The Many Ways to Install a Network Operating System   Full install versus upgrade   Installing over the network   Automate...
Using Internet Connection Sharing Mapping Network DrivesChapter 7: Verifying Your Network Installation Is the Computer Con...
Patching your servers Securing Your UsersChapter 3: Managing User Accounts Exploring What User Accounts Consist Of Looking...
Fixing Dead Computers Ways to Check a Network Connection A Bunch of Error Messages Just Flew By! Double-Checking Your Netw...
Assessing Different Types of Disasters   Environmental disasters   Deliberate disasters   Disruption of services   Equipme...
Configuration information provided by DHCP   DHCP servers   How DHCP actually works Understanding Scopes   Feeling exclude...
Creating an FTP site Changing the FTP site properties Adding content to your FTP siteAccessing an FTP Site with a BrowserU...
rmdir   send   status   trace   type   user   verboseChapter 6: TCP/IP Tools and Commands Using the arp Command Using the ...
Home on the Range Wireless Network Adapters Wireless Access Points   Infrastructure mode   Multifunction WAPs Roaming   Wi...
Checking for Obvious Problems Pinpointing the Problem Changing Channels Fiddle with the Antennas Adding Another Access Poi...
Deciding whether to upgrade or install   Considering your licensing options   Thinking about multiboot   Choosing a file s...
Local accounts versus domain accounts   User account properties Creating a New User Setting User Properties   Changing the...
Using the Computer Management Console Working with ServicesChapter 8: Windows Commands Using a Command Window   Opening an...
Creating Web SitesChapter 2: Managing Exchange Server 2010 Creating a Mailbox Managing Mailboxes   Enabling Mailbox Featur...
Linux: It Isnt Windows   X Window   Virtual consoles   Understanding the file system On Again, Off Again   Logging on   Lo...
Chapter 6: Running Apache Installing Apache Starting and Stopping Apache Confirming that Apache Is Running Using the HTTP ...
The ls command   The cp command   The rm command   The mv command   The touch command   The cat command Commands for Worki...
Smartphones            Appendix B: Glossary                                    Networking Basics                    Chapte...
All networks, large or small, require specialized network hardware to make them work. For smallnetworks, the hardware may ...
♦ Network software: Although network hardware is essential, what really makes a network work issoftware. A whole bunch of ...
The distinction between servers and clients in a network would be somewhat fun to study in a sociologyclass because its si...
the same city but are far enough apart that the networks cant be connected using a simple cable orwireless connection.Netw...
sends a duplicate copy of the packet to all its ports. In contrast, a switch knows which computer isconnected to each of i...
A third type of network topology is called a ring, shown in Figure 1-3. In a ring topology, packets are sentaround the cir...
Mesh networks arent very practical in a LAN setting. For example, to network eight computers in a meshtopology, each compu...
♦ 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 ...
The Seven Layers of the OSI Reference ModelOSI sounds like the name of a top-secret government agency you hear about only ...
The first three layers are sometimes called the lower layers. They deal with the mechanics of howinformation is sent from ...
The Data Link LayerThe Data Link layer is the lowest layer at which meaning is assigned to the bits that are transmitted o...
of addressing each packet so that its delivered to the intended recipient, and a way to ensure that two ormore nodes dont ...
An important function of the Data Link layer is to make sure that two computers dont try tosend packets over the network a...
Although the exact format of logical addresses varies depending on the protocol being used, mostprotocols divide the logic...
The Transport layer is the layer where youll find two of the most well-known networking protocols: TCP(normally paired wit...
TCP is a connection-oriented Transport layer protocol. UDP is a connectionless Transport layerprotocol.The Session LayerTh...
such as SMB. The data then works its way down through the protocol stack. Along the way, the protocol ateach layer manipul...
The Ethernet ProtocolAs you know, the first two layers of the OSI model deal with the physical structure of the network an...
♦ 10BaseT: Unshielded twisted-pair cable (also known as UTP) became popular in the 1990s because itseasier to install, lig...
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  1. 1. Exam CramCCNA Practice Questions (Exam 640-802) Third Edition Jeremy Cora, CCIE No. 11727
  2. 2. 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
  3. 3. 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
  4. 4. 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
  5. 5. 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. 6. 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
  7. 7. 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
  8. 8. 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
  9. 9. 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
  10. 10. 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
  11. 11. 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
  12. 12. 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
  13. 13. 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?
  14. 14. 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.
  15. 15. 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
  16. 16. Table of ContentsIntroduction
  17. 17. 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
  18. 18. 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
  19. 19. 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
  20. 20. 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
  21. 21. 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
  22. 22. 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
  23. 23. 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
  24. 24. 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
  25. 25. 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
  26. 26. 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
  27. 27. 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)
  28. 28. 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
  29. 29. 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
  30. 30. 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
  31. 31. 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
  32. 32. 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
  33. 33. 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
  34. 34. 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
  35. 35. 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
  36. 36. 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
  37. 37. 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
  38. 38. 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.
  39. 39. ♦ 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.
  40. 40. 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
  41. 41. 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
  42. 42. 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
  43. 43. 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.
  44. 44. 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.
  45. 45. ♦ 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.
  46. 46. 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.
  47. 47. 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.
  48. 48. 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
  49. 49. 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.
  50. 50. 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 207.120.67.30. 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.
  51. 51. 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
  52. 52. 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
  53. 53. 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,
  54. 54. 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.
  55. 55. 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.
  56. 56. ♦ 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

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