UNIX System Administration Handbook, Third Edition

14.1 PACKET FORWARDING: A CLOSER LOOK

Before we jump into the management of routing tables, let’s take a more detailed look at how the tables are used. Consider the network shown in Exhibit A.

Exhibit A Example network

Router R1 connects the two Ethernets, and router R2 connects one of the nets to the outside world. (For now, we’ll assume that R1 and R2 are UNIX computers rather than dedicated routers.) Let’s look at some routing tables and some specific packet forwarding scenarios. First, host A’s routing table:

A% netstat -rnRouting tablesDestination           Gateway              Flags    Refs    Use            If127.0.0.1            127.0.0.1             UH       6         563131      lo0 ...