The Transmission Control Protocol/Internet Protocol (TCP/IP) maps to both the Open System Interface (OSI) and DoD (Department of Defense) models but maps more closely with the DoD model because the Department of Defense was the original creator and user of this protocol. In Table 3 you can see where TCP and IP map to the DoD model as well as some other common protocols in use on typical local area networks. Table 3. Viewing the DoD Model with TCP/IP Mapped to It
TCP/IP is the basic communication language or protocol of the Internet. Many other protocols are available out there, some of which you may be familiar with, such as AppleTalk, IPX/SPX, even SNA. All these protocols have been displaced by TCP/IP, however. Because most networks today are connected to the Internet somehow, using only TCP/IP makes more sense. TCP/IP is responsible for creating and keeping communications between all network-connected devices that need to communicate with each other. Without the need for communication, TCP/IP would serve no true purpose, but because the whole purpose of a network is to share resources, TCP/IP is the medium that provides such communication. Couple this need for communication with some form of physical topology (cabling or wireless), and you have a network. An IP address is a 32-bit number that denotes a node or host on a network. The number, which resembles 10.1.1.1/24, is a unique host on a single network. If you have two nodes, one numbered 10.1.1.1 and 10.1.1.2, they are able to communicate if they are connected to the same network segment and no other outstanding issues stop communication. An IP address is broken down into two specific parts : the network identifier and host identifier. Let's look at the following IP address to understand it better:
You need to break down this number into binary bits to truly see what we mean by masking. First, consider the fact that you have a 32-bit address written in decimal format. If you want to see the subnet mask 255.255.255.0 in binary, you have to change the format from decimal to binary, or base 2 numbering, as follows :
Remember, binary uses only 1s and 0s, either on or off. No other numbers are used, so you can see how the network is masked. All 1s in the network portion denote the actual network you are working on. This leaves the host portion (the 0s at the end) available for assignment. This way, any device can know what network it's on, or better, what subnet. Because we've used 24 1s here, we denote the IP address as 10.1.1.0/24. Using this form of notation is an easier way to show a subnet mask assignment. If you see /30, for example, the address appears like this in binary:
Public IP addressing uses three major spaces: Classes A, B, and C. There are also two more classes: Class D, which is used for multicast-based networks, and Class E, which is still experimental. Class A is for very large networks, Class B is for medium- sized networks, and Class C is used for networks that have no more than a couple hundred nodes. Public ranges are shown in Table 4. Table 4. Viewing IP Address Classes
Notice that 127 is not listed in the address range. The IP address 127.0.0.0 is reserved for loopback networks and testing. 127.0.0.1 is also located in the HOSTS file, which allows you to test the IP connectivity of your own machine. If you use the command ping loopback (which is the hostname located in the HOSTS file), you can resolve to 127.0.0.1, and you should see a reply. This way, you know that TCP/IP is configured properly ”at least on your own system. Although the private IP address ranges shown in Table 5 fall within Class A, B, and C public IP addresses, note that private IP addresses are not routable on the Internet by design (and by default) and should never be seen outside an internal network. Table 5. Viewing Private IP Classes
When implementing a new network, you should know what you want the network to look like before you even contemplate ordering gear to populate it. This step is important because you must consider many factors before implementation. These factors include the following:
IPX/SPX, which stands for Internetwork Packet Exchange/Sequence Packet Exchange, is similar to TCP/IP. You can think of IP mapping to IPX and TCP mapping to SPX. These protocols perform similar operations. IPX/SPX was originally created and used extensively by Novell with its NetWare platform of network operating systems. Although IPX/SPX was a great protocol, TCP/IP became the protocol of the Internet. To avoid missing out on the Internet revolution, all NOS vendors chose to develop TCP/IP into all their solutions moving forward, leaving in other protocols such as IPX/SPX only for backward compatibility. Novell NetWare version 5.0 was the first version to be shipped with a real version of TCP/IP, whereas the older versions of NetWare (versions 4.x and before) used add-on packs . Systems Network Architecture (SNA) is an old but still widely used protocol. Developed by IBM, SNA is a protocol suite that runs on most mainframes used today. Microsoft professionals who know only Microsoft may be shocked to learn that in today's networks they most likely will be confronted with some form of mainframe and may also be responsible for network connectivity to it. Another old protocol, the Network Basic Input/Output System (NetBIOS) is a session layer communications service used by client and server applications in IBM-based token-ring and PC LAN Ethernet-based networks. NetBIOS is really just a way for application programming interface “based communications to take place. This means that higher-level services can run over lower-level protocols such as IP. This process is known as NetBIOS over TCP/IP (NBT). The NetBIOS service contains three main sections: the name , session, and datagram services. To connect your LAN to the Internet, you need to plan for the following:
When troubleshooting client-based TCP/IP problems, you must develop a good troubleshooting methodology; otherwise , you will be wasting your time. If you cannot make a client resolve names properly because its client-side DNS cache is either corrupted or not updated to a change already made on the DNS server, you can easily flush out that information by using one of the following commands:
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