Our discussion in the previous chapter dealt with static routing. The routing table entries were created by default when an interface was configured (for directly connected interfaces), added by the
route command (normally from a system bootstrap file), or created by an ICMP redirect (usually when the wrong default was used).
This is fine if the network is small, there is a single connection point to other networks, and there are no redundant routes (where a backup route can be used if a primary route fails). If any of these three conditions is false, dynamic routing is normally used.
This chapter looks at the dynamic routing protocols used by routers to communicate with each other. We concentrate ...