The routing performed by IP, when it searches the routing table and decides which interface to send a packet out on, is a routing mechanism. This differs from a routing policy, which is a set of rules that decides which routes go into the routing table. The Net/3 kernel implements the routing mechanism while a routing daemon, typically
gated, implements the routing policy. The structure of the routing table must recognize that the packet forwarding occurs frequently hundre ds or thousands of times a second on a busy system w hile routing policy changes are less frequent.
Routing is a detailed issue and we divide our discussion into three chapters.
This chapter looks at the structure of ...