By default, all Windows operating systems use the TCP/IP protocol suite to communicate with each other through network devices. Any computer network adaptor using TCP/IP requires 3 things to communicate with other computers: An IP address, a subnet mask for that IP address, and a default gateway. These terms will be defined in a moment. First, though, an idea of how a TCP/IP network works logically.

When you give a computer an IP address, you identify the network which it is a member of, and give it an identification number within that network. A computer in a given network can communicate with any other computer that is local to it (in the same network), provided there is a way for information to pass between them (network cables, wireless network, etc.).

Computers in a network cannot, however, communicate with computers in a different network (remote network) directly, even if they are physically connected to each other via cables.

This is where the default gateway comes in. A gateway is defined as a path out of the local network to other remote networks. A gateway can be a number of things physically, such as a DSL/cable router for your local network, a Windows server computer with multiple network adaptors split between different networks, etc. Gateways must all share one thing in common though. They are connected to at least 2 networks, and have the ability to pass traffic between them.

The default gateway assigned to a network adaptor is sent all traffic that does not belong in the local network. As an example of this, say you have a DSL Internet connection. When you connect to the Internet, you are provided with a default gateway assigned by your service provider. When you attempt to connect to a site on the Internet, the URL you type in (say www.pcstats.com) is converted into an IP address by your Internet provider.

Since this address is not going to be in your local network, the network adaptor in your computer forwards the request for the web page to its default gateway, your service provider.

From that point, your request will be passed from network to network through the internet until it reaches the local network of www.pcstats.com and the data needed to display the web page starts its way back through the internet to your IP address.

That isn't where IP addresses stop, as you'll discover next.