Routing is one of the most important functions of IP. Figure 9.1 shows a simplified view of the processing done at the IP layer. Datagrams to be routed can be generated either on the local host or on some other host. In the latter case this host must be configured to act as a router, or datagrams received through the network interfaces that are not ours are dropped (i.e., silently discarded).
Figure 9.1. Processing done at the IP layer.
In Figure 9.1 we also show a routing daemon, which is normally a user process. The most common daemons used on Unix systems are the programs
gated. (The term daemon means ...