Default gateway

When information has to be forwarded from a computer on one network to a computer on another network, a special network device called a router must be used. The router has a table that lists all the networks it knows about and the network ID associated with each of those networks. When the router receives information destined for a particular IP address, it checks its table of network IDs for a match. If a match is found, it delivers the information to the appropriate network.

How does the information get to the router so that it can be forwarded? Looking back to the example from Table below in the previous section, Computer A has information for Computer B, and Computer A realizes that Computer B sits on a different network. At this point, Computer A looks at its default gateway, which is the address of the router that will forward the information on to Computer B's network. The default gateway is a TCP/IP option configured on each workstation. Typically, all computers on the same network point to the same router.

Now that you are comfortable with the concepts of an IP address, subnet mask, and default gateway, you're ready to configure these options on a Windows operating system, which is covered in the next section.

Configuring TCP/IP in Windows 2000/XP/2003

To configure TCP/IP on a newer system, such as Windows XP, you need to go to your local area connection properties and configure the TCP/IP protocol. Be aware that all Microsoft operating systems today have TCP/IP installed by default. You simply need to configure the IP address on the system. To configure TCP/IP on a Windows 2000/XP/2003 system, follow these steps:

1. If you're using Windows 2000, choose Start → Settings → Control Panel → Network and Dial Up Connections. If you're using Windows XP/2003, choose Start → Control Panel → Network and Internet Connections → Network Connections.
2. Right-click your local area connection and choose Properties.
3. In the list of items used by the connection, select TCP/IP and click Properties.
4. To assign a static address, select Use the Following IP Address and then type your computer's IP address, subnet mask, and default gateway in the corresponding text boxes.
5. Type the address of your DNS server in the Preferred DNS Server text box.
   In order to know what to type as the IP address of your DNS server you will need to consult the network administrator or maybe even the network architects. Whoever has designed the network knows the IP address of the DNS server. (DNS is covered in more detail in the section "DNS," later in this tutorial.)
6. Click OK and then OK again.