Networking Protocols

An Introduction to TCP/IP

TCP/IP (Transmission Control Protocol/Internet Protocol) is more difficult than other protocols, because there are so many options to configure. This brief introduction should provide a better understanding of many of the options.

Many other protocols, such as NetBEUI and IPX/SPX require no configuration. TCP/IP however seems at first sight to have an endless number of options and therefore appears difficult. In reality it is nowhere as bad as it seems, but it is essential to have some understanding of what it is that you are configuring. This chapter is intended to cover the most important points.

The IP Address

This is the most basic element of TCP/IP. The IP address is a number that is unique to each computer. If you know a computers IP address you can communicate with that computer from anywhere in the world. TCP/IP is the protocol that the Internet uses. This means that TCP/IP must be routable. When you try to access an IP address you computer must be able to tell whether or not the address is located on the local network, if it is there will not be a problem reaching it. If it is not TCP/IP must know on which network it is located in order to find the address.

The network number represents the network that contains any given IP address. Looking through the tabs on the TC/IP properties sheet, you will see that there is nowhere to specify the network number. The network number is part of the IP address.

An IP address is made up of a network number and a computer number. A computer can distinguish the two numbers because of what is known as the sub-net mask. This is located in a field directly below the IP address on the properties sheet. A simple sub-net mask would be 255.255.0.0. The numbers making up the sub-net mask indicate which portion of the IP address is the network address and which is the individual computer number. The four numbers in the sub-net mask correspond directly to the four numbers in the IP address. For example, if a computer has an IP address of 172.100.80.42 and a sub-net mask of 255.255.0.0. The first two numbers, both 255, indicate that the first two numbers of the IP address are the network number and the second two numbers, both zero, indicate that the second two numbers are the computer number. This means that in the above address 172.100 denote the network that the computer is on and the 80.42 indicate which computer it is on that network. This is a very simple example sub-net masks may be much more complex. An individual network may for instance be sub-divided.

The Default Gateway

TCP/IP attaches to a "foreign" network by using Routing tables. These are stored in the routers and tell the router where to connect in various situations.

One of the TCP/IP configurations is for a default gateway. This is the address a TCP/IP packet is sent to if it can not find the address on the local network. This is usually a router that controls the local network's link to the outside world (often through an Internet connection). This router has a table of addresses of other routers. The destination IP address helps the router determine to which router to pass the packet. A TCP/IP packet will normally pass through several routers before it arrives on the destination network and ultimately the destination computer.

DHCP

Dynamic Host Configuration Protocol (DHCP) allows you to set one or more servers on the network as a DHCP server. When a client computer set to use the DHCP option comes on line the DHCP server automatically configures TCP/IP on this computer. This means that once the DHCP server has been configured it is not necessary to configure each computer separately. IT also prevents the accidental use of an IP address more than once. It is also useful if you only have a limited number of IP addresses to work with as only the computers that are turned on will use an IP address.

WINS

On Windows based networks each computer has a name. The WINS option can be configured to contain the IP address of a Windows NT server that is running a WINS service. The WINS service resolves computer (NetBIOS) names to IP addresses. If an attempt is made to contact a computer by its name the WINS database is searched for the name and IP address. It will not have to query every computer on the network to determine the correct IP address. This reduces network traffic considerably.

DNS

DNS manages domain names rather than computer names. A domain name is the type of name that is used on the Internet. Kingshurst.co.uk is a domain name. When a browser is pointed to a domain name the computer will query a DNS server for the IP address of that domain. If the DNS server does not know the address it asks another DNS server, a process, which continues until it finds one that knows the address. At that point that server informs all the DNS servers involved in the chain and your computer of the domain's IP address

   Back