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Chapter 2: Network ProtocolsTerms you'll need to understand:
- OSI reference model
- Subnet mask
- Packet filtering
- Knowing the differences between routable and nonroutable protocols
- Implementing and configuring multiple network protocols
- Installing and managing TCP/IP packet filters
Protocols are sets of rules that define how computers and components interact with one another. They are developed either by a single entity or by an organization made up of a group of entities. The International Organization for Standardization (ISO), located in Geneva, Switzerland, is responsible for developing and publishing standards. This group designed a standard that is used as a model for network communication, the Open Systems Interconnection (OSI) reference model.
The OSI Reference ModelNetwork communication is a complex process, requiring that participating parties all be "on the same page." Having a set of rules to follow increases the chance that information will be exchanged, which is why the OSI reference model was designed. The model is a guide for developers to follow when creating or implementing a protocol.
The OSI model is divided into seven layers. Each layer defines a part of the network communication process, by specifying the layer's function in transmitting data on the network. Network communication is information passed between the layers. Each layer is directly related to the layer above it and the layer below it. The following are the OSI reference model layers:
- Physical layer-Responsible for putting the data on the medium.
- Data Link layer-Defines how the data is accessed from the medium and how it is put on the medium.
- Network layer-Makes sure the information has the address of where it needs to go.
- Transport layer-Provides error-checking and makes sure the information arrives.
- Session layer-Establishes communication channels between hosts.
- Presentation layer-Formats the information.
- Application layer-Defines the way applications interact with the network.
The first thing you need is a telephone, a piece of hardware you can buy at the store. After you purchase a telephone, it does you no good (meaning you can't communicate with Joe) until you take the next step, which is plugging it into the wall jack. Even after plugging it into the wall, you can't communicate with Joe until you pick up the phone and ensure you have a dial tone. You have to dial his phone number, you have to make sure the person who answers the phone speaks your language, and you have to make sure that Joe eventually gets on the line. After you have done all this, you then need to explain the information to Joe in a way that he can understand it. After this is done, Joe can then apply the information you have communicated to him.
Let's see how this illustrates the OSI model.
- Physical layer-The telephone
- Data Link layer-The dial tone
- Network layer-The phone number
- Transport layer-The correct language
- Session layer-Joe getting on the line
- Presentation layer-The format for the information that Joe understands
- Application layer-Joe using the information you communicated to him
Note: It is important to note that different protocols can work at different layers of the OSI model. Some protocols only work at one layer, but others work at more than one layer.
Network connectivity devices also function at different levels of the OSI model. Hubs, media, repeaters, and network interface cards all function at the Physical layer. Switches and bridges function at the Data Link layer. Routers (default gateways) function at the Network layer, and gateways (protocol translators) typically function at the Application layer.
Protocols Supported by Windows 2000Just as there are many different languages in the world, there are many different types of protocols. In Windows 2000, the protocols supported are:
- NetBIOS Enhanced User Interface (NetBEUI)
- NWLink Internetwork Packet Exchange/Sequenced Packet Exchange (IPX/SPX)
- Data Link Control (DLC)
- Transmission Control Protocol/Internet Protocol (TCP/IP)
NetBIOS Enhanced User Interface (NetBEUI)NetBEUI is a small and fast protocol used by Microsoft operating systems. Some of the documentation you see concerning NetBEUI also mentions the word efficient. That is debatable. If efficient means getting to where it needs to go with no regard for network traffic, then yes, it is efficient. However, if efficient takes into account network traffic, then no, it is not.
NetBEUI works at the Transport layer; therefore, it has a reliable delivery aspect. NetBEUI was designed for smaller networks because the protocol has a tendency to be chatty. Chatty means it is broadcast based, and you don't want a lot of chat happening in a network.
In Windows 2000, NetBEUI is in version 3 and is known as NetBIOS Frame (NBF). NBF is Microsoft's implementation of the NetBEUI protocol on Windows 2000 computers. If you have a network of 20 or fewer Windows 2000 computers, NetBEUI is a good choice, unless you need to segment your network or get to the Internet. The minute you start putting routers in your network, all bets are off concerning NetBEUI. NetBEUI is not routable, and therefore you cannot use it as the protocol of choice for large networks that are segmented by routers.
Note: NBF does support routing on an IBM Token-Ring network.
The Windows 2000 version of NetBEUI has fewer limitations on it, such as the 254-session connection limitation that existed with the original NetBEUI -protocol.
When NetBEUI is installed on a Windows 2000-based computer, you do not need to configure the protocol. If you really want to, however, you can change the default values for NetBEUI in the Registry. The NetBEUI startup entries appear under the following subkey:
Only make changes to the Registry if you cannot find the appropriate tool in the Microsoft Management Console (MMC).
If you have multiple network interface cards (NICs) in your computer, do not bind NetBEUI to more than one card on the same physical network or on bridged Ethernet segments. The reason is that NetBEUI tries to register the name from all NICs, and you get a duplicate name error.
Another funny thing about NetBEUI is that if you have a Windows 2000 computer running only NetBEUI, it receives the master browser list from the master browser running NetBEUI. Browsing on a computer running Windows 2000 happens per protocol. The client uses one protocol at a time. It first tries one, and then uses another if it doesn't receive a response. This might cause problems with Windows 2000 computers running only TCP/IP or some other network protocol, where the computer does not receive a completely accurate browse list.
NWLink Internetwork Packet Exchange/Sequenced Packet Exchange (IPX/SPX) NWLink is Microsoft's implementation of the IPX/SPX protocol developed by Novell. As the name indicates, it is really two different protocols that operate at different levels of the OSI model. IPX functions at the Network layer, defining addressing on a NetWare network. SPX functions at the Transport layer, providing reliability.
Unlike NetBEUI, NWLink is routable. Because of this capability, this protocol is better suited for larger networks that use routers. Although this protocol is included with Windows 2000, it is usually only used in networks that include NetWare servers. NWLink assists with NetWare client/server applications running Winsock. Windows 2000 clients that need access to files and print services on NetWare servers must install Client Services for NetWare or Gateway Services for NetWare. NWLink installs automatically when you install Client Services for NetWare or Gateway Services for NetWare. For NetWare clients that need to access files and print services on Windows 2000 servers, there is File and Print Services for NetWare.
AppleTalkWindows 2000 supports the AppleTalk protocol, which was developed by Apple. The AppleTalk protocol is not used as a communications protocol between Windows 2000 computers. It is only used to accommodate Macintosh computers. AppleTalk is routable and therefore can be implemented in larger networks. There is a caveat: Windows 2000 Server uses the AppleTalk protocol to allow Macintosh clients to access file and print services that are installed if the Windows 2000 server is also running File Services for Macintosh and Print Services for Macintosh.
Data Link Control (DLC)Data Link Control is a protocol used primarily to connect Windows 2000 computers to IBM mainframe computers or to access Hewlett-Packard JetDirect printers. DLC is not used for network communication between Windows 2000 computers or any Microsoft operating systems.
TCP/IPVolumes have been written on the subject of TCP/IP, its history, its uses, and its possible future. This chapter will not contain a complete discussion of TCP/IP. The purpose of this section is to give a basic background and to examine TCP/IP in relation to the Windows 2000 exam objectives.
TCP/IP is really a suite of protocols. In other words, it consists of a number of protocols that together effect network communication. It is the most open of all the protocol stacks, and for this reason, it is the most utilized. Open in this sense means that no single vendor controls it, unlike IPX/SPX or AppleTalk, which are owned by Novell and Apple, respectively. Almost every operating system supports TCP/IP, and Windows 2000 is no exception.
The TCP/IP reference model is an example of how protocols work together to effect network communications. Microsoft uses a four-layer model for its TCP/IP stack that maps nicely to the OSI reference model. All the protocols in the TCP/IP suite are contained in the following four layers:
- Application layer
- Transport layer
- Internet layer
- Network Interface layer