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    Web Developer Foundations: Using XHTML Bonus Networking Chapter Web Developer Foundations: Using XHTML Bonus Networking Chapter Document Transcript

    • Web Developer Foundations: Using XHTML Bonus Networking Chapter Chapter: Networking for Web Developers This chapter introduces networking topics for web developers. The concepts of networking categories, topologies, components, architecture, protocols, and troubleshooting are discussed. While the role of web developer does not usually include administering a network, a web developer needs to be able to communicate effectively with network administrators and network engineers. This chapter should provide a foundation for that communication. Learning Outcomes In this chapter, you will learn to: • Describe the categories of networking • Describe network topologies • Describe network operating systems • Describe network architecture • Describe the physical components of networks • Describe the OSI Reference Model • Describe common networking protocols • Describe Internet addressing • Describe network troubleshooting tools • Describe servers used on the Internet and Web Categories of Networking A network consists of two or more computers connected together for the purposes of communication and sharing resources. Networked computers can share Copyright © 2002 Terry Felke 11/13/02 Page Network-1
    • Web Developer Foundations: Using XHTML Bonus Networking Chapter files and share peripherals such as printers and scanners. There are three major networking categories: peer-to-peer, server-based, and enterprise. • Peer-To-Peer Network In a peer-to-peer network (shown below) all the nodes (computers) on the network have a similar relationship to the others. In this non-hierarchical relationship, each node can have access to resources associated with the other nodes. Examples of PC operating systems which allow peer-to-peer networking include: Microsoft Windows 95/98/Me, Novell NetWare Lite, Artisoft LANtastic, and Microsoft Windows for Workgroups. Peer-to-Peer Local Area Networks (LANs) are typically set up in small organizations or home networks. • Server-Based Network A diagram of a server-based network is shown below. This type of network contains one or more server computers in addition to network node computers. Copyright © 2002 Terry Felke 11/13/02 Page Network-2
    • Web Developer Foundations: Using XHTML Bonus Networking Chapter The server computers are typically very fast and contain large (and often multiple) hard drives. The server computer is called the file server, network server, or just the "server". The server typically contains resources such as files or databases that the node computers need to access. Peripheral devices such as printers can be attached to the server, node computers, or directly connected to the network. The server provides security and control for network resources. Examples of server-based network operating systems include: UNIX, Linux, Novell NetWare, Microsoft Windows NT, Microsoft Windows 2000, Digital Advantage Networks (DECnet), and Apple AppleTalk network for Macintosh. • Enterprise Network Enterprise networks may include both peer-to-peer and server-based networks. The enterprise network provides connectivity between all nodes in an organization, regardless of their location or architecture type; and typically support more than 500 active users at one time. Enterprise networks often contain gateways that provide connectivity between different network architecture types. Network Topologies The physical layout of the cables that connect the nodes of the network is called the topology of the network. Common network topologies include bus, star, and ring topologies. These are described below. • Bus Topology When using Bus Topology, all nodes are attached to the communications line directly and all signals are seen by each of the nodes. See the figure below for a diagram of this topology. Copyright © 2002 Terry Felke 11/13/02 Page Network-3
    • Web Developer Foundations: Using XHTML Bonus Networking Chapter When a node sends data, it is transmitted to all nodes on the network. Each node has a unique identity and can recognize those signals intended for it. Nodes ignore the data if it is not intended for them. In a bus topology, hardware called Terminators is placed on the ends of the cable to prevent the data signals from echoing through the network. Bus topology is reliable yet relatively simple and inexpensive to implement. Because all the nodes are on the same line, isolating problems can be difficult and the network traffic will slow during peak load periods. Data collisions can occur because traffic can flow in both directions on the bus and multiple nodes can transmit at any given time. • Star Topology In networks that use star topology (shown below) all network nodes are connected through a central device, usually a hub. Copyright © 2002 Terry Felke 11/13/02 Page Network-4
    • Web Developer Foundations: Using XHTML Bonus Networking Chapter This has an advantage in reliability over bus topology in that if a single cable fails, the rest of the network can still operate. However, a large disadvantage is that if there is a problem with the central device (hub), the entire network may be inoperable. • Ring Topology When using ring topology, the network nodes are connected to each other in a circular chain. See the diagram below. The final node connects to the first node to complete the ring. As the data travels along the ring, each node examines the destination address. If the data is not meant for the node, the node passes the data along the ring. Data always flows in one direction on the ring, and only one “token” of data exists at any time. This Copyright © 2002 Terry Felke 11/13/02 Page Network-5
    • Web Developer Foundations: Using XHTML Bonus Networking Chapter provides an advantage over bus topology in that collisions are eliminated. Ring networks typically perform well during heavy network traffic. A disadvantage to the ring is that if a single connection is broken, the entire network is inoperable. • Hybrid Network Topology An enterprise network or a large network created over time at an organization may combine bus, star, and ring topologies. The networks are connected with hardware called routers. An advantage of using hybrid network topology is ease of expansion of an organization's networks. • Mesh Topology A network that is configured using mesh topology contains nodes that are connected with multiple paths to provide redundancies in the network. All devices are cross-connected. This allows the best path to be chosen at any particular point in time. Topology is just one aspect of a network of computers. Another aspect that a web developer should be aware of is the network operating system being used. Network Operating Systems The purpose of a network operating system (NOS) is to manage resources on a network. A NOS manages printer sharing, common file and database sharing, application sharing, user identification, and security for the network. A NOS enables client machines to access remote drives on the server or other client machines. In client/server networks, the NOS is the operating system that runs on the server. The client computers must have portions of the NOS software installed. Commonly used network operating systems are UNIX, Microsoft Windows NT, Microsoft Windows 2000, Microsoft Windows .NET Server, Novell NetWare, and Linux. Interoperability is the ability of one system to communicate with another – different Copyright © 2002 Terry Felke 11/13/02 Page Network-6
    • Web Developer Foundations: Using XHTML Bonus Networking Chapter operating systems working together. All of the popular network operating systems can interoperate with each other. It is not uncommon for large organizations to have Novell NetWare severs, Windows Servers, and UNIX servers all connected to the same enterprise network. Popular network operating systems are discussed below. • Microsoft Windows NT (New Technology) Microsoft Windows NT, first released in 1995, provides a graphical user interface to administer small and large networks. When using this popular NOS, Windows NT Server is installed on the server and Windows NT Workstation is usually installed on the client. Windows NT uses TCP/IP as the default network protocol. • Microsoft Windows 2000 Server This NOS is Microsoft’s replacement for Windows NT. It features improvements in reliability and security. It also provides an Active Directory, which enables a company to set up virtual private networks, to encrypt data locally or on the network, and to give users access to shared files in a consistent way from any network computer. Windows 2000 uses TCP/IP as the default network protocol. There are three versions of Windows 2000 for servers. Windows 2000 Server is useful for small to medium sized businesses. Windows 2000 Advanced Server is intended to be used as a network server or application server. Windows 2000 Datacenter Server is designed for large data warehouses and applications requiring high-speed computations and large databases. Windows 2000 Professional is usually installed on the client. • Microsoft Windows .NET Server This NOS is meant to replace Windows 2000 Server. The .NET Server NOS also is available in multiple versions, including the Standard Server, Enterprise Server, and Datacenter Server. In addition to the expected improvements in reliability and security, the .NET Servers provide additional functionality – Copyright © 2002 Terry Felke 11/13/02 Page Network-7
    • Web Developer Foundations: Using XHTML Bonus Networking Chapter including the integration of an application environment to develop XML Web services and business solutions. Visit Microsoft’s web site for more information. Windows .NET Servers use TCP/IP as the default network protocol. • Novell NetWare Novell NetWare is a widely installed network operating system. Various versions of Novell network operating systems have been in place since the 1980s. Novell NetWare uses servers that provide services such as file storage and network printing. A recent version is Novell NetWare 6, which uses TCP/IP as its networking protocol and can be remotely configured. Earlier versions of NetWare (before Netware 5) used proprietary protocols – Internetwork Packet Exchange (IPX), Sequenced Packet Exchange (SPX), and NetWare Core Protocol (NCP) – instead of TCP/IP. • UNIX The UNIX operating system is was developed at AT&T Bell Labs in the late 1960s. It was designed as a multi-user operating system and is ideal for a networked environment. UNIX has a long history of supporting TCP/IP. It is very scalable and is available for almost any platform. UNIX is a command-driven, text-based operating system. However, there are GUI window environments applications such as X-Windows available. Popular versions of UNIX include Sun Solaris, IBM AIX, and HP-UX. Linux is a popular derivative of UNIX. [sidebar] Web Developer Perspective: Why do I care about knowing which Network Operating System (NOS) my web host provider uses? Knowing the NOS used by your web host provider is important because it can help you with troubleshooting your web site. Often students’ web sites work great on their Copyright © 2002 Terry Felke 11/13/02 Page Network-8
    • Web Developer Foundations: Using XHTML Bonus Networking Chapter own PC (usually with a Windows-based operating system) but “fall apart” (with broken links and images that do not load) after being published to a free web server that uses a different operating system. Some operating systems, such as Windows, treat upper- and lowercase letters in exactly the same way. Other operating systems, such as UNIX and Linux, consider upper- and lowercase letters to be different. This is called being “case sensitive”. For example, when a web server running with on a Windows Operating System receives a request generated by an anchor tag coded as “<a href=”MyPage.htm”>My Page</a>” it will return a file named with any combination of upper or lowercase letters. “MyPage.htm”, “mypage.htm”, “myPage.htm” could all be used. However, when the request generated by the same anchor tag is received by a web server running on a UNIX system (which is case sensitive) the file would only be found if it were really saved as “MyPage.htm”. If the file were named “mypage.htm”, a 404 (not found) error would result. This is a good reason to always be consistent when naming files – consider always using lowercase letters for file names. [end of sidebar] • Linux Linux was developed in the early 1990s by Linus Torvaldas. It is a version of UNIX designed to run on PCs. Linux has grown in popularity because it is free, open-source software. Linux includes a graphical user interface and utilizes TCP/IP. Difficulties associated with using Linux include the small selection of commercial software and hardware device drivers available for this platform. Some large companies, such as IBM, are supporting Linux as an alternative to Microsoft operating systems. IBM has released a version of its Universal Database for the Linux platform. Commercial versions of Linux are available from vendors such as Red Hat and Caldera. Copyright © 2002 Terry Felke 11/13/02 Page Network-9
    • Web Developer Foundations: Using XHTML Bonus Networking Chapter Now that you've had an introductory overview of network categories, topologies, and operating systems, let’s continue with a discussion of network architecture and components. Network Architecture You have studied network categories and topologies. Now you are ready to take a look at how networks are put together: Local Area Networks, Wide Area Networks and the internetworking architecture of the Internet. Local Area Network (LAN) A LAN is a group of computers connected within a confined geographical area – usually a building or group of buildings. Your school computer lab uses a LAN. If you work in an office, you probably use a computer connected to a LAN. Recently, many people have begun to set up LANs in their homes to share resources between computers. Common LAN technologies include Ethernet and Token Ring. Wide Area Network (WAN) A WAN is a group of computers connected over a dispersed geographic area. For example, an organization with offices on both the east and west coasts of the United States probably uses a WAN to provide a link between the LANs at each of the offices. See below for a diagram of this connectivity. Copyright © 2002 Terry Felke 11/13/02 Page Network-10
    • Web Developer Foundations: Using XHTML Bonus Networking Chapter Internet Backbone A backbone is a large transmission line that carries data gathered from smaller lines that interconnect with it. On the Internet a backbone is a set of paths that local or regional networks connect to for long-distance interconnection. The Internet is a group of interconnected networks – the Internet Backbones provide very high-speed connectivity. An image of the AT&T IP Backbone map (from http://www.ipservices.att.com/backbone/index2.cfm) is shown in below. Note the connections between major cities, or Network Access Points (NAPs). If you are interested in maps of the Internet, visit An Atlas of Cyberspaces (http://www.cybergeography.com/atlas/geographic.html) • Network Access Point (NAP) Access points or junctions to the Internet Backbone are called Network Access Points (NAPs). Chicago, New York, and San Francisco are three key NAPs in the United States. Visit the Chicago NAP's web site (http://www.aads.net/main.html) Copyright © 2002 Terry Felke 11/13/02 Page Network-11
    • Web Developer Foundations: Using XHTML Bonus Networking Chapter to view photos of the actual hardware used and find out which Internet Service Providers are connected directly to the NAP. • Segment A segment is used in network architecture to describe a part of a large structure. This could be used to indicate part of the Internet Backbone or part of a regional connection. Segments can also be used to describe subnetworks in a LAN. Network Components As you read the previous sections you might have been wondering – what about the hardware? What about all the devices that use the protocols and physically connect the computers together? This section focuses on Network components – the hardware. • Network Interface Card (NIC) Every node on a network contains a Network Interface Card (NIC). The card usually is located in an expansion slot on the motherboard of a desktop or tower personal computer. Notebook computers use PCMCIA NICs. The NIC connects to the network with some type of network cable media. Each NIC that is manufactured contains a unique MAC or Media Access Control address. This is used to identify the device to other network devices. • Repeaters Repeaters re used to extend LAN segments. This device amplifies the incoming signal received from one segment and sends it on to the next segment. Using repeaters allows you to extend the network beyond ordinary distance limitations. • Hubs A hub is a device that is used to connect computers on the same local network in Copyright © 2002 Terry Felke 11/13/02 Page Network-12
    • Web Developer Foundations: Using XHTML Bonus Networking Chapter a star topology. A hub has several ports, and each network computer (or node) connects to a separate port. Hubs can also be connected to other hubs, switches, and routers. • Bridges Bridges are used to connect network segments in the same LAN. They can reduce the amount of network traffic by dividing a network into two segments. Bridges can also be used to connect network segments using different protocols. Bridges use MAC (media access control) hardware addresses as the basis for limiting network traffic. • Switches Switches select a path or circuit for sending a packet to the proper pot, reducing network traffic in a manner similar to bridges. Switches operate more intelligently than simple network devices such hubs and repeaters. Switches are increasingly replacing these older devices. Switches do not share bandwidth in the same manner that hubs do; they can devote the entire bandwidth to a single node if needed. Servers can also connect directly to switches. • Routers The role of a router is to direct network packets. A router identifies the packet's destination address and determines the best path to the destination. The router sends the packet to either the next closest router or to the actual destination network, if that network is connected to the router. A router will create or maintain a table of the available routes and their conditions and use this information along with distance and cost algorithms to determine the best route for a given packet. Copyright © 2002 Terry Felke 11/13/02 Page Network-13
    • Web Developer Foundations: Using XHTML Bonus Networking Chapter An addressing structure supported by the addressing protocol (IP or IPX) must be used. Routers are dynamic and can update their routing tables "on the fly". RIP (Routing Information Protocol) is a protocol used for dynamically managing routing tables. • Brouters Brouters contain the functionality of both bridges and routers. They can route traffic to a variety of networks and are protocol-independent. • Gateways A gateway is a network point that acts as an entrance to another network. A gateway is often used to connect two networks using different network protocols. For example, a gateway would be used to connect a Novell IPX/SPX network to a Windows 2000 TCP/IP network. • Modems Modems enable computers to use telephone lines to communicate with other computers. A traditional analog modem modulates outgoing digital signals from a computer to analog signals for a conventional telephone line. When a modem receives the signal over a telephone line it demodulates the incoming analog signal and converts it to a digital signal for the receiving computer. Modems are also used to connect computers to cable, DSL, and ISDN networks. In these cases, there is no translation to analog; the term modem is used to describe the physical device that connects the computer to the outside network or digital phone line. Copyright © 2002 Terry Felke 11/13/02 Page Network-14
    • Web Developer Foundations: Using XHTML Bonus Networking Chapter • Patch Panel A patch panel s used to provide a central connection point where cables from different rooms or departments can be connected to networking devices to form a LAN. A patch panel consists of a group of network cabling sockets mounted on a rack. It is usually placed in a secure closet. Transmission Media Networks are comprised of computers, devices, network software, and transmission media – the component that connects everything together. This section discusses some commonly used types of transmission media. • Twisted Pair Cable This is the most widely used media in modern ethernet networks. Twisted pair is formed by twisting two insulated copper wires around each other. A twisted pair segment cannot be more than 100 meters in length. That is why network devices such as repeaters are used. There are a number of categories of twisted pair. A commonly used category is Category 5 (Cat5). Cat5 contains four twisted pairs and can transmit data up to 100 Megabits per second. • RJ-45 Connectors RJ-45 (Registered Jack-45) connectors are used with twisted pair cabling in ethernet and token ring networks. They look similar to RJ-11 modular phone connectors, but are larger. • Coaxial Cable This is a high-capacity cable used for communication and video networks. Copyright © 2002 Terry Felke 11/13/02 Page Network-15
    • Web Developer Foundations: Using XHTML Bonus Networking Chapter Coaxial (coax) is two-wire cable where the inner wire is the conductor and the metal sheath around it is a ground. In general, coax provides higher bandwidth than twisted pair cable. o Thick Coaxial Cable (thicknet) This coax works well for environments such as hospitals where machines produce electromagnetic radiation that would interfere with other types of cable. It does not bend easily but has a maximum segment length of 500 meters.This is usually used in networks to transmit at 10 Megabits per second. o Thin Coaxial Cable (thinnet) This is an ethernet standard for smaller networks. It is more flexible and easier to install. The maximum segment length for thinnet is 185 meters. This is usually used in older networks to transmit at 10 Megabits per second. • Fiber Optic Cables This type of cable can transmit data much faster than other cable types – in the range of gigabits per second. Fiber Optic Cables consist of two strands: one to receive and one to send. The transmission of data is sent as pulses of light and can travel for miles without degrading. Fiber Optic Cables are expensive compared to other transmission media types. • Wireless A Wireless LAN is one in which a mobile user can connect to a local area network using a wireless (radio) connection. Each node on the wireless LAN needs a wireless NIC transceiver. The IEEE 802.11 standard specifies the technologies for wireless LANs. Copyright © 2002 Terry Felke 11/13/02 Page Network-16
    • Web Developer Foundations: Using XHTML Bonus Networking Chapter The wireless access point device shown above is physically connected to a network with cable, allowing one or more remote PCs with wireless NICs to receive the signals from the wireless access point and access the network. You have studied network topologies, operating systems, and components. You may be wondering how the computers connected to networks communicate with each other. This is accomplished by networking protocols – rules for network communication. Common Networking Protocols A protocol is a standard set of rules that allow a client and server to communicate. Both the client and the server must follow the same set of rules, or protocols, in order to communicate. Protocols are often based on industry standards or international standards. Commonly used protocols are described below: • TCP/IP TCP/IP, Transmission Control Protocol/Internet Protocol, has been adopted as the official protocol of the Internet. The current version is TCP/IP version 4. A newer version, known as IPv6 is currently being tested. CP and IP have different functions that work together to ensure reliable communication over the Internet. The purpose of TCP is to ensure the integrity of the communication. TCP breaks messages and files into multiple "packets". These contain information such as the destination, source, sequence number, and checksum values. Copyright © 2002 Terry Felke 11/13/02 Page Network-17
    • Web Developer Foundations: Using XHTML Bonus Networking Chapter IP then takes over and uses IP addressing to send each packet over the Internet using the best path at the particular time. When the destination address is reached, TCP verifies the integrity of each packet using the checksum, requests a resend if a packet is damaged, and reassembles the file or message from the multiple packets. As mentioned above, IP routes each packet to the correct destination address. What actually happens is that the packet gets fowarded to the next closest router (a hardware device designed to move network traffic) until it reaches its destination. Each device connected to the Internet has a unique numeric IP address. IPv4 uses 32-bit addressing – this results in a decimal number in the format of xxx.xxx.xxx.xxx, where each “xxx” is a value from 0 to 255. The IP address may correspond to a domain name. For example, at the time this was written the IP address of Yahoo! was 216.115.108.245. Copyright © 2002 Terry Felke 11/13/02 Page Network-18
    • Web Developer Foundations: Using XHTML Bonus Networking Chapter You can enter this number in the Address text box in a Web Browser (as shown in Figure12.18), press Enter, and the Yahoo home page will display. Of course – it’s much easier to type yahoo.com which is why the Domain Name System was created in the first place! Other protocols that are part of the TCP/IP suite include User Datagram Protocol (UDP), Internet Control Message Protocol (ICMP), and Address Resolution Protocol (ARP). • IPX/SPX This is a protocol developed by Novell and once dominated LANs and WANs. IPX, Internetwork Packet Exchange, handles network addressing and routing. SPX, Sequenced Packet Exchange, provides reliability and ensures that the packets arrive undamaged. IPX/SPX is used mainly with Novell products. Even though IPX/SPX is not supported on the Internet, it is widely used for private networks and WANs. • NetBEUI NetBEUI (pronounced “net-boo-ee”) is a protocol used for Microsoft peer-to-peer networks. The acronym stands for Network Basic Input/Output System Extended User Interfaces. NetBEUI was originally developed by IBM. • Apple-Talk Apple-Talk is proprietary and is only used in Apple networks. • Data Link Control (DLC) This protocol was also originally developed by IBM. It was later adopted by Hewlett-Packard to connect laser printers to LANs. • Systems Network Architecture (SNA) This is IBM's mainframe network architecture and was introduced in 1974. It is Copyright © 2002 Terry Felke 11/13/02 Page Network-19
    • Web Developer Foundations: Using XHTML Bonus Networking Chapter still widely used within mainframe networks. Large networks often use both TCP/IP and IXP/SPX. Small peer-to-peer networks sometimes use NetBEUI. As a web developer it will not be your role to select a protocol for the network. However, you may need to work with a test web server. In this case the network protocol must support TCP/IP. You have been introduced to common networking protocols. However, we still haven’t discussed how the communication between client and server takes place. Let’s take a look at the OSI Reference Model, a conceptual model that describes this process. OSI Reference Model The International Organization for Standardization developed the OSI/RM, Open Systems Interconnect Reference Model, in the early 1980s. This is a conceptual model that describes how information from a software application in one computer moves through a network medium to a software application in another computer. The OSI/RM is composed of seven layers. Each layer specifies particular network functions. OSI Layers Layer Layer Function Network Number Name Components 7 Application This layer processes end-user and Client or Server end-application protocols: telnet, Computer ftp, http, smtp, pop3. 6 Presentation Application data is either packed Client or Server or unpacked to be ready by the Computer running application. Protocol conversions, Copyright © 2002 Terry Felke 11/13/02 Page Network-20
    • Web Developer Foundations: Using XHTML Bonus Networking Chapter encryption/decryption and graphics expansion occur at this layer. 5 Session Provides for two communicating Client or Server presentation entities to exchange Computer data with each other. 4 Transport This is where TCP lives! This layer Client or Server ensures data reliability and Computer. integrity. 3 Network IP protocol is at this layer. Routers and Layer 3 Provides a means to establish, Switches (Routing maintain and terminate network switches) operate at connections. All routers in a this layer. Brouters network operate at this layer. operate at layer 3 and layer 2. 2 Data Link This layer defines the access Network devices such strategy for sharing the physical as bridges and medium, including data link and switches operate at media access issues. Protocols this layer. such as PPP live here. The MAC Brouters operate at address – the six-byte number layer 3 and layer 2. unique to each NIC – may be LAN switches forward used by this layer traffic based on MAC address at this layer 1 Physical This layer defines the physical and The NICs, repeaters, Copyright © 2002 Terry Felke 11/13/02 Page Network-21
    • Web Developer Foundations: Using XHTML Bonus Networking Chapter electrical characteristics of the hubs, and switching network. hubs run at this layer – passing strings of zeros and ones down the pipe. Packets and the OSI The illustration in Figure 12.17 showed a very basic packet structure. Recall that a packet is a piece of information transmitted on a network. When a web browser is used to visit a web site, the request is placed in one or more packets that travel through the Internet. The figure below illustrates the process of a packet taking this journey. The request begins at the Application Layer (Layer 7) and moves down through the layers to the Physical Layer (Layer 1). The layers of protocols can each add their Header Copyright © 2002 Terry Felke 11/13/02 Page Network-22
    • Web Developer Foundations: Using XHTML Bonus Networking Chapter to the packet. Once the Physical Layer is reached, the message (consisting of the packet and its associated Headers) is transmitted as bits (1s and 0s) across the network. Once received at the destination address, the Headers are stripped off and processed by each layer until the data is presented to the host application such as a web browser, web server, or email application. Internet Architecture Layers The OSI/RM is a conceptual reference model for network architecture. The architecture of the Internet has used TCP/IP since 1983. The table below lists both the standard OSI/RM model and the Internet Protocol Suite of the TCP/IP Stack. Notice how the functions of the top three layers of the OSI are combined into a single Application Layer in the Internet Protocol Suite. OSI Layer Internet Protocol Function Suite Application Application This layer processes end-user and end-application protocols: telnet, ftp, http, smtp, pop3. Application data is either packed or unpacked to be ready by Presentation the running application. Protocol conversions, graphics expansion, and encryption/decryption occur at this layer. Provides for two communicating Session presentation entities to exchange data with each other. Transport TCP/UDP This layer ensures data reliability and integrity. Network IP Provides a means to establish, maintain and terminate network connections. All routers in a network operate at this layer Copyright © 2002 Terry Felke 11/13/02 Page Network-23
    • Web Developer Foundations: Using XHTML Bonus Networking Chapter Data Link Data Link This layer defines the access strategy for sharing the physical medium, including data link and media access issues. Protocols such as PPP live here. Network devices such as bridges and switches operate at this layer. Physical Physical This layer defines the physical and electrical characteristics of the network. The NIC cards and interfaces on the routers run at this level – passing strings of zeros and ones to the communications media. Internet Protocol Suites are defined, standardized, and revised by the IETF using Requests for Comments (RFC). If you are interested in viewing the RFCs related to Internet Protocols, visit http://www.rfc-editor.org/rfcxx00.html. The role of IP (Internet Protocol) in establishing network communication, or Internet Addressing, was mentioned above. How does the request for a web page entered in your browser find the correct web server in the Internet? How are the computers identified? Let’s take a look at Internet Addressing. Internet Addressing When a web page is requested, the IP part of TCP/IP places the requesting IP Address in the Header (along with other information) and the message packet is sent (by routers) to the IP address of the web server. The TCP/IP protocol at the web server responds and transmits the web page packets to back to the requestor's IP Address (by way of routers). Copyright © 2002 Terry Felke 11/13/02 Page Network-24
    • Web Developer Foundations: Using XHTML Bonus Networking Chapter Internet Protocol uses classes of addresses to uniquely identify hosts and networks on the Internet or any network that uses TCP/IP protocol. An IPv4 Address is a 32-bit (binary digit) number. It is represented by four decimal numbers separated by periods, called dotted decimal, in the format xxx.xxx.xxx.xxx. Each group of “xxx” is a decimal number ranging from 0 to 255 that represents 8 bits (binary digits) and is called an "octet". This provides for a potential 232 or approximately 4 billion IP Addresses. An IP Address has two parts: the network portion and the host or workstation portion. IP Network Addresses are assigned by ICANN (http://www.icann.org), the Internet Corporation of Assigned Names and Numbers. They are categorized by Address Classes, which can support different numbers of hosts and workstations. • Class A is intended for large networks with potentially millions of devices. Class A IP Addresses range from 0.xxx.xxx.xxx to 126.xxx.xxx.xxx. The network portion is the first octet and the host portion uses the remaining three octets. 27.135.134.209 is an example of a Class A IP Address. • Class B is intended for medium-sized networks with potentially thousands of devices. Class B IP Addresses range from 128.0.xxx.xxx to 191.255.xxx.xxx. The network portion is the first two octets and the host portion uses the last two octets. 132.35.134.209 is an example of a Class B IP Address. • Class C is intended for small networks with no more than 254 devices. Class C IP Addresses range from 192.0.0.xxx to 223.255.255.xxx. The network portion is the first three octets and the host portion is the last octet. 208.35.134.209 is an example of a Class C IP Address. A table depicting the network and host portions of Class A, Class B, and Class C IP Addresses is shown below. 8 bits 8 bits 8 bits 8 bits xxx xxx xxx xxx Copyright © 2002 Terry Felke 11/13/02 Page Network-25
    • Web Developer Foundations: Using XHTML Bonus Networking Chapter Class A Network Host Host Host Class B Network Network Host Host Class C Network Network Network Host • Class D addresses are multicast addresses. Class D IP Addresses range from 224.0.0.0 to 239.0.0.0. • Class E is an experimental class. Its IP Addresses range from 240.0.0.0 to 247.0.0.0. A table that describes the number of networks and hosts in Class A, Class B, and Class C is shown below. Class Network Octets Number of Host Octets Number of Host Networks Addresses A 0.xxx.xxx.xxx to 127 xxx.0.0.1 to 16 million 126.xxx.xxx.xxx xxx.255.255.254 B 128.0.xxx.xxx to 16,000 xxx.xxx.0.1 to 65,534 191.255.xxx.xxx xxx.xxx.255.254 C 192.0.0.xxx to 2 million xxx.xxx.xxx.1 to 254 223.255.255.xxx xxx.xxx.xxx.254 Since Class A IP Addresses are meant for large networks, their address structure can accommodate the largest number of hosts. Class C is useful for smaller networks. Notice how many more IP Addresses can be accommodated with Class A IP address than a Class C IP Address. If you are curious about who has been assigned a particular network IP Address, check out the ARIN database at http://www.arin.net/whois/index.html. Copyright © 2002 Terry Felke 11/13/02 Page Network-26
    • Web Developer Foundations: Using XHTML Bonus Networking Chapter Did you notice some numbers "missing" from the discussion of IP Addresses? There are some special IP Addresses reserved for private networks, loopback addresses and broadcast address purposes. • Private IP Addresses are used on private TCP/IP networks that are isolated from the Internet. The IP Address ranges are: 10.0.0.0 to 10.255.255.255, 172.16.0.0 to 172.31.255.555, and 192.168.0.0 to 192.168.255.255. • The Broadcast Address is 255.255.255.255. Messages with this IP Address as the destination is sent to all hosts on a network. • The Loopback Address is 127.0.0.1. Use this when you need to test your own workstation. If your workstation is running a web server and you type http://127.0.0.1 in your web browser, you will access your web site. • The IP Address 0.0.0.0 is currently unassigned and is used temporarily when a computer requests an IP Address to be dynamically assigned to it. The IP Addresses above are standard, but another method is in place to work around the limitations of the IP Address Classes. This method is called CIDR (Classless Inter-Domain Routing). CIDR is a method to allocate and specify the Internet addresses for inter-domain routing more flexibly than with the original system of IP Address classes. CIDR is now the routing system used by virtually all gateway hosts on the Internet's backbone. An overview of CIDR can be found at http://public.pacbell.net/dedicated/cidr.html. Although CIDR has helped, with the increasing numbers of mobile phones, automobiles, and PDAs connected to the Internet there is a danger of running out of IP Addresses. That is where the next version of IP, IPv6, saves the day. Copyright © 2002 Terry Felke 11/13/02 Page Network-27
    • Web Developer Foundations: Using XHTML Bonus Networking Chapter IPv6 IPv6, Internet Protocol Version 6, is the most recent version of the Internet Protocol. IPv6 was designed as an evolutionary set of improvements to the current IPv4 and is backwardly compatible with it. Service providers and Internet users can update to IPv6 independently without having to coordinate with each other. IPv6 provides for more Internet Addresses because the IP address is lengthened from 32 bits to 128 bits. This means that there are potentially 2128 unique IP Addresses possible, or approximately 340,282,366,920,938,463,463,347,607,431,768,211,456. (Now there will be enough IP addresses for everyone’s PC, notebook, cell phone, pager, PDA, automobile, toaster, etc.!) Another improvement in IPv6 is the provision for three types of addressing: unicast (one host to one other host), anycast (one host to the nearest of multiple host), and multicast (one host to multiple hosts). For more information on IPv4 and IPv6 Internet Addressing, view the whitepaper at http://www.3com.com/solutions/en_US/ncs/501302.html. This chapter continues with a discussion of how to configure your computer or workstation to use TCP/IP on a network. TCP/IP Workstation Configuration There are a number of configurations needed when setting up a computer to use TCP/IP, including IP Address, Subnet Mask, Default Gateway, and DHCP Client. This section discusses those terms and settings. To configure a Windows PC to use TCP/IP, the Network Properties Dialog Box is used. Select Start, Settings, Control Panel, Network to display the Network Properties Dialog Box, shown below. Copyright © 2002 Terry Felke 11/13/02 Page Network-28
    • Web Developer Foundations: Using XHTML Bonus Networking Chapter To close the dialog box without saving any inadvertent changes, click the Cancel button. To view and configure the TCP/IP Properties, highlight the TCP/IP entry that corresponds to your NIC in the Network Components select box and then click the Properties button. Your network administrator determines how IP addresses are assigned on the network. The IP address of your computer may be a specific, static address. Another option is to configure each computer to request and obtain an IP address each time it connects to the network. The next section takes a look at Subnet Masks, which are needed for static IP addressing. Subnet Mask A subnet mask is used to distinguish the between the network and host portions of an IP Address on a network. Because it does this, it can be used to determine Copyright © 2002 Terry Felke 11/13/02 Page Network-29
    • Web Developer Foundations: Using XHTML Bonus Networking Chapter whether a destination address is local or remote. Like an IP Address, a subnet mask is a 32-bit number. While subnet masks can be custom configured, this section will focus on the default subnet masks. The Default Subnet Masks for Class A, B, and C IP Addresses are shown below. Class D and Class E IP Addresses do not have hosts and do not need subnet masks. Class IP Address Range Default Subnet Mask A 0.xxx.xxx.xxx to 126.xxx.xxx.xxx 255.0.0.0 B 128.0.xxx.xxx to 191.255.xxx.xxx 255.255.0.0 C 192.0.0.xxx to 223.255.255.xxx 255.255.255.0 In the table above, "255" indicates that all 8 bits in the octet are "1s" bits are on and signifies the network portion of the IP Address. "0" indicates that all 8 bits in the octet are "0s" and signifies the host portion of the IP Address. For example, to configure a host on a Class C Private Network, the sample IP Address is 192.168.56.1. The subnet mask of "255.255.255.0" indicates that the network portion of the address is "192.168.56" and the host portion is "1". Copyright © 2002 Terry Felke 11/13/02 Page Network-30
    • Web Developer Foundations: Using XHTML Bonus Networking Chapter Default Gateway The default gateway is usually set to the IP Address of a router to be used when the destination is remote and not part of the Local Area Network. See the example in Figure 12.22. Copyright © 2002 Terry Felke 11/13/02 Page Network-31
    • Web Developer Foundations: Using XHTML Bonus Networking Chapter DHCP Client DHCP (Dynamic Host Configuration Protocol) lets a network administrator supervise and distribute IP addresses from a central point and automatically sends a new IP address when a computer is connected to the network. When an organization sets up its computer users with a connection to the Internet, an IP address must be assigned to each machine. Without DHCP, the IP address must be entered manually at each computer. DHCP dynamically assigns a new IP address each time the computer is connected to the network. The advantage of DHCP is that is more efficiently utilizes IP host addresses by allocating them only when they are needed. The screen shot in Figure 12.22 shows a request to obtain an IP Address automatically. Copyright © 2002 Terry Felke 11/13/02 Page Network-32
    • Web Developer Foundations: Using XHTML Bonus Networking Chapter Your network administrator or Internet service provider will supply you with the values for these configuration settings. However, what if everything doesn't work perfectly? What are some methods to use to identify the problem? The next section discusses standard networking diagnostic tools and utilities. Diagnostic Tools This section will introduce some commands and utilities that are helpful when troubleshooting a network or a website. They are run from a Command window. Select Start, Programs, MS-DOS Prompt to open a Command Window to try the diagnostic tools below. Copyright © 2002 Terry Felke 11/13/02 Page Network-33
    • Web Developer Foundations: Using XHTML Bonus Networking Chapter It's Not Working? Depending on your school's computer lab security settings, you may not be able to access a Command window. Even if you can display a Command Window, your school may have blocked some of these commands for security reasons. Command Window Hints Command or Key Purpose Combination cls Clears the screen in the Command Window Ctrl + C Cancels processing in the Command Window exit Closes the Command Window > file name This directs the output of a command to the file name you specified. For example: “ping yahoo.com > myping.txt” will send the output of the ping command to a text file named “myping.txt”. | more This directs the output of a command to the “more” utility, which will display one screen at a time and prompt you for “more”. For example: “tracerte yahoo.com | more” will allow you to page through the trace route display. The ping Utility This is used to test connectivity between source and destination systems. Ping stands for Packet Internet Groper. Ping determines whether or not there is a connection between the source system (your computer) and the destination system (the website or network you are trying to reach). The syntax is: Copyright © 2002 Terry Felke 11/13/02 Page Network-34
    • Web Developer Foundations: Using XHTML Bonus Networking Chapter ping IP Address or ping Domain Name Try launching a Command Window and typing "ping yahoo.com". A sample screen shot is shown below. This shows the IP Address of Yahoo! and the time needed for the packet to travel the round trip from your computer to Yahoo! and again. This is measured four times. If you are connected to a network, try pinging the computer you are using. Test your own TCP/IP configuraion by trying the Loopback address, 127.0.0.1. Your result should be similar to the one shown below. Copyright © 2002 Terry Felke 11/13/02 Page Network-35
    • Web Developer Foundations: Using XHTML Bonus Networking Chapter The tracert Utility This is used to determine the path or route between the source and destination systems. It also shows the time in milliseconds between hops in the route. Each “hop” is the next router in the path to the destination. The syntax is: tracert IP Address or tracert Domain Name Try launching a Command Window and typing "tracert isoc-chicago.org". A sample screen shot is below and shows the path from the source computer, located on a network in the suburban Chicago area to the destination computer, located in downtown Chicago. If you prefer a more visual listing, try out the Visual Trace Route Application at http://www.visualroute.com/server.html. Copyright © 2002 Terry Felke 11/13/02 Page Network-36
    • Web Developer Foundations: Using XHTML Bonus Networking Chapter The netstat Command This is used to display the contents of data structures related to the network. The options will vary with the Operating System. Launch a Command Window and type "netstat -?" to determine the options available to you. The syntax is: netstat or netstat options A screen shot of "netstat -a" to display all connections and listening ports is shown below for a computer named "peace". The ipconfig Command The ipconfig Command is used with Windows NT and Windows 2000 (but also works with Windows 95 and Windows 98). This is used to display the IP Configuration. The syntax is: ipconfig options or Copyright © 2002 Terry Felke 11/13/02 Page Network-37
    • Web Developer Foundations: Using XHTML Bonus Networking Chapter ipconfig /All The parameter "/All" will display all the IP-related configuration information. See a sample screen shot below The winipcfg Command The winipcfg Command is used with Windows 95, Windows 98, and Windows Me. This is used to display a dialog box that shows the network IP Configuration for your computer. The syntax is: winipcfg Another way to launch this command is to select Start, Run, and type in "winipcfg", click OK. A screen shot of the IP Configuration is shown below. The arp Command The purpose of the arp command is to display Address Resolution Protocol (ARP) information. ARP is used to resolve software addresses (such as IP Addresses) to hardware addresses (such as MAC or Adapter Addresses). The syntax to display the Arp cache is: arp -a Copyright © 2002 Terry Felke 11/13/02 Page Network-38
    • Web Developer Foundations: Using XHTML Bonus Networking Chapter This section has provided you with an overview of tools that can be used to diagnose web site and network problems. As a web developer, you may need to use these tools when connectivity problems initially occur. Contact your network administrator or network engineer to resolve the problems. Your network administrator may need to analyze the network traffic to investigate the problem. Commercial tools that perform this function are described next. Network Analyzers Commercial applications can be purchased that will monitor, capture, and analyze network traffic. These can be useful in establishing a baseline and monitoring the state of the network over time. They are also helpful in troubleshooting network slowdowns and bottlenecks. A partial screen shot of a packet viewed with an analyzer is shown below. More information about network analyzers may be found at Sniffer (http://sniffer.com), Agilent (http://www.network-analyzer.com/) and Ethereal (http://ethereal.planetmirror.com/). Copyright © 2002 Terry Felke 11/13/02 Page Network-39
    • Web Developer Foundations: Using XHTML Bonus Networking Chapter The next section completes our overview of networking concepts with a discussion of port numbers and servers used on the Internet. Port Numbers When using TCP/IP, a Port Number is used by a client program (such as a web browser) to specify a particular server program (such as a web server). Certain applications that use TCP/IP such as the Web protocol, HTTP, have ports with pre- assigned numbers. These are "well known ports" that have been assigned by the Internet Assigned Numbers Authority (IANA). Other application processes are given port numbers dynamically for each connection. Port numbers range from 0 to 65535. Ports 0 to 1023 are reserved for use by certain privileged services. For example, port 80 is the default for HTTP, port 20 and port 21 are reserved for FTP, port 25 is reserved for SMTP. See the IANA list of Well Known Port Numbers at http://www.iana.org/assignments/port-numbers. Servers Used on the Internet In a traditional client/server network, the purpose of the server is to share files, databases, and applications with the client nodes on the network. With an interconnected network of computer networks – the role of the server becomes more diversified and there are a number of types of servers used. This section discusses the more common types of servers. • File Server The purpose of a file server is to store data files and programs on a network. • Print Server The purpose of a print server is to allow multiple users to print to the same physical printer. A print queue stores print requests until they are transmitted to the printer. Copyright © 2002 Terry Felke 11/13/02 Page Network-40
    • Web Developer Foundations: Using XHTML Bonus Networking Chapter • Web Server Web servers use HTTP and listen for web page requests on Port 80, the port assigned to HTTP. Popular web server software includes Apache Web Server, Microsoft Internet Information Server, Personal Web Server, and iPlanet Server. • Proxy Server The purpose of a proxy server is to act as an intermediary between a network host and the destination server. Proxy servers perform a number of functions, including security, content filtering, and caching. A proxy server can act as a firewall and allow only HTTP traffic through to the network. • Media Server A media server transmits streaming audio and streaming video. Streaming media formats generally use UDP (User Datagram Protocol) instead of TCP. UDP is well suited to transmitting pieces of data quickly. It does not retransmit data if there is an error. This is acceptable for video and audio because small errors in the transmission will unlikely be noticed. A popular streaming media server is RealNetworks RealSystem. • Domain Name System Server The Domain Name System (DNS) was developed to translate host computer names into IP Addresses. It corresponds the domain names typed in Web browsers to the physical computers connected to the Internet. For example, “yahoo.com” translates to 216.115.108.243. The Domain Name System is decentralized; there is no single Domain Name database. Rather, the DNS is distributed on name servers all over the Internet. • FTP An FTP (File Transfer Protocol) server is used to upload and download files from Copyright © 2002 Terry Felke 11/13/02 Page Network-41
    • Web Developer Foundations: Using XHTML Bonus Networking Chapter a computer connected to the Internet. Sending files with FTP is quicker than using HTTP or sending them as attachments to email. • News Server The purpose of a news server is to provide access to newsgroups and to allow the creation of new newsgroups. News severs use the Network News Transfer Protocol (NNTP). In order to access a news group, a user needs to launch a news reader application such as Microsoft Outlook or Netscape Communicator. • Certificate Server The purpose of a certificate server is to validate keys that act as a form of identification on the Internet or an Intranet. Keys and certificates will be discussed in Chapter 13. • Mail Server The purpose of a mail server is to store and forward email messages. Several protocols are used. SMTP (Simple Mail Transfer Protocol) is used to send email. POP3 (Post Office Protocol) and IMAP (Internet Message Access Protocol) are used to receive email messages. • Transaction Server A transaction server is a program that runs on an Internet or other network server and manages application and database transactions on behalf of a client computer user. • Database Management System A database management system (DBMS), sometimes just called a database manager, is a program that lets one or more computer users create and access data in a database. In a web application, the DBMS will frequently be on a Copyright © 2002 Terry Felke 11/13/02 Page Network-42
    • Web Developer Foundations: Using XHTML Bonus Networking Chapter separate machine from the web server in order to maximize the processing of both. MIME Types MIME (Multi-Purpose Internet Mail Extensions) is a set of rules that allow mulitmedia documents to be exchanged among many different computer systems. MIME was initially intended to extend the original Internet e-mail protocol, but it is also used by HTTP. MIME provides for the exchange of seven different media types on the Internet: audio, video, image, application, message, multipart, and text. MIME also uses subtypes to further describe the data. The MIME type of a web page is "text/html". MIME types of gifs and jpeg images are image/gif and image/jpeg respectively. A Web server determines the MIME type of a file before it is transmitted to the Web Browser. The MIME type is sent along with the document. The Web browser uses the MIME type to determine how to display the document. Summary This chapter provided an overview of networking concepts. As a web developer you should have a general understanding of networking terms related to the Web and Internet. This makes you a more well-rounded professional and better able to communicate with the network administrators and network engineers you will need to work with during your career. For a more detailed study of networking concepts, consider taking a course in Networking. Another good way to learn about networking is to actually do it! If you've got two computers at home, you can connect them in a peer-to-peer network and start learning hands-on! Visit the course web site at http://www.webdevfoundations.net for examples, updated information, and the links listed in this chapter. Copyright © 2002 Terry Felke 11/13/02 Page Network-43
    • Web Developer Foundations: Using XHTML Bonus Networking Chapter Review Questions Multiple Choice. Choose the best answer. 1. When using _____________ topology, the network nodes are connected to each other in a circular chain. a. Bus b. Star c. Ring d. Loop 2. The purpose of a ___________________ is to manage resources on a network. a. network operating system b. network topology c. network architecture d. none of the above 3. A _________________ amplifies the incoming signal received from one network segment and sends it to the next. a. switch b. hub c. repeater d. network interface card 4. The official protocol of the Internet is ________________. a. OSI Reference Model b. TCP/IP c. star Copyright © 2002 Terry Felke 11/13/02 Page Network-44
    • Web Developer Foundations: Using XHTML Bonus Networking Chapter d. none of the above 5. This is a conceptual model that describes how information from a software application in one computer moves through a network medium to a software application in another computer. a. OSI Reference Model b. TCP/IP c. router topology d. none of the above 6. A ___________is a group of computers connected over a dispersed geographic area. a. Local Area Network (LAN) b. Metropolitan Area Network (MAN) c. Wide Area Network (WAN) d. none of the above 7. When using ______________, a network administrator can supervise and distribute IP addresses from a central point and automatically assign a new IP address when a computer connects to the network. a. DHCP b. CGI c. OSI d. none of the above 8. When using TCP/IP, a ___________ is used by a client program (such as a web browser) to specify a particular server program (such as a web server). Copyright © 2002 Terry Felke 11/13/02 Page Network-45
    • Web Developer Foundations: Using XHTML Bonus Networking Chapter a. MIME type b. subnet mask c. hub d. none of the above 9. Use the __________ utility to test connectivity between source and destination systems. a. ipconfig b. tracert c. ping d. netstat 10. The major function of a ________ is to transmit streaming audio and streaming video. a. web server b. media server c. proxy server d. domain name server Hands-On Exercises 1. Experiment with network diagnostic tools. a. Check out your computer configuration. Use the information provided in the chapter as a guide and run either ipconfig or winipcfg. Do a screen print of the results. b. Run the ping utility on your favorite web site. Use the information provided in the chapter as a guide. Do a screen print of the results. Notice that the ping utility Copyright © 2002 Terry Felke 11/13/02 Page Network-46
    • Web Developer Foundations: Using XHTML Bonus Networking Chapter displays the IP address of the target server and sends packets to the target server four times. Note the round-trip travel times for those packets. Why aren’t all the times exactly the same? Explain. c. Run the tracert utility on your favorite web site. Use the command syntax provided in the chapter as a guide. Do a screen print of the results. Notice the number of “hops” that were needed to travel the route between your computer and your favorite web site. Are you surprised? Why or why not? Web Site Case Study There are no Case Study assignments this chapter. Web Research A. Find out the following about the network at your school or place of employment: • Network Topology(s) • Network Operating System(s) • Number of server computers • Number of client computers • Network address class Create a web page that lists the results of your research. Search the Web for background information on the Network Operating System(s) being used. Organize your page with a table that lists the information. Place your name in an e-mail link on the web page. Print both the source code (from Notepad) and the browser view of your web page. B. Wireless Access to the Web is a topic of growing importance. Search the Web and find information to justify why your school or employer should consider wireless acces for their local area networks. Create a web page that informs the reader about your findings. Include URLs of the web sites you used as resources. Place your name in an e- Copyright © 2002 Terry Felke 11/13/02 Page Network-47
    • Web Developer Foundations: Using XHTML Bonus Networking Chapter mail link on the web page. Print both the source code (from Notepad) and the browser view of your web page. C. Visit any of the web sites referenced in the chapter that interested you. Print the home page or one other pertinent page from the site. Create a web page that discusses the web site you visited. Your new web page will use a table for layout, and include the use of color and images. Write a one page summary and reaction to the web site you chose to visit. Address the following topics: 1. What is the purpose of the site? 2. Who is their intended audience? 3. Do you believe they reach their audience? 4. Was this site useful to you? Why or why not? 5. List one interesting fact or issue that this site addressed. 6. Would you encourage others to visit this site? 7. How could this site be improved? Chapter Review Answers 1. c 2. a 3. c 4. b 5. a 6. c 7. a 8. d 9. c Copyright © 2002 Terry Felke 11/13/02 Page Network-48
    • Web Developer Foundations: Using XHTML Bonus Networking Chapter 10. b Copyright © 2002 Terry Felke 11/13/02 Page Network-49