When configuring TCP/IP settings on your home network, only an IP address and subnet mask are explicitly required. However, if you want your computers to be able to communicate with outside networks (like the Internet), you will also need to configure a default gateway IP address. The default gateway is the IP address to which packets destined for outside networks are sent by default. To be clearer, the default gateway is the IP address of a router connected to the local network. For home users, this would be the internal IP address of your hardware router, or of the computer configured as a NAT server (such as a Windows XP system running ICS). Just remember that if you need to communicate with an outside network like the Internet, you will need to configure a default gateway IP address as well.