Troubleshooting connectivity problems on a TCP/IP network is probably the most frequent troubleshooting process that any desktop administrator or home user will go through. Having a basic understanding of how TCP/IP works can make the troubleshooting process slightly easier for you.

Computers running Windows Vista (and earlier versions) default to TCP/IP as the networking protocol. Each computer that runs TCP/IP requires a unique Internet Protocol (IP) address and subnet mask to communicate with other computers on the network. A computer also requires the IP address of a default gateway and a DNS server to communicate with computers outside of the local area network (LAN), such as computers on the internet or on other subnets.

There are three different ways that a computer can obtain IP configuration information:

• The computer is manually assigned an IP address through the TCP/IP Properties window
• The computer is configured to locate a DHCP Server that will dynamically assign it an IP address
• The computer is configured to locate a DHCP server, but doesn’t find one, in which the system is assigned a number in the 169.254.x.x range with a 255.255.x.x subnet

When you attempt to access another computer on the same network, your computer compares its IP address and subnet mask with that IP address and subnet mask assigned to the destination computer. If they match appropriately, you can successfully connect to the other computer. If they do not match, the process that occurs is very similar to a letter where the address and the zip code do not match. If you are attempting to access a computer that is outside the boundaries of your LAN, the computer quickly determines this, and refers your computer to the default gateway (usually a router) to essentially ‘leave town’ (which is the LAN) and take the road to wherever it goes, which is usually an Internet Service Provider. Subsequent routers determine the best place for your computer to go, and the data reaches either its destination or it dies trying. Now, that’s pretty simple, and pretty much all that you need to know in order to do most of the troubleshooting.