A system uses its routing table to identify which network interface to use when sending packets to remote systems. For a system with only a single interface, configuring the IP address of a gateway system on the local network suffices to route packets to other networks. For example, see the image Figure 2-5, which shows a field where you can enter the IP address of the default gateway.

On systems that have several IP interfaces, you can define static routes so that traffic for a special host or network is forwarded to that network through the default gateway. You use the same tools to configure routing as you do to configure network interfaces.