8.1. Routing Protocol Primer

Originally, all of the connections between routers were manually entered static routes. Each router had to have an entry for every network, along with explicit paths by which to reach those other networks. Every time one network was added, every router had to be manually configured with an entry for that network. In addition, if a failure occurred, these entries would have to be changed, again manually, to route around the break. This could cause quite an administrative headache to monitor as a network grew.

Dynamic routing protocols solved this administrative nightmare by enabling routers to tell each other of the networks to which they were connected. They also allowed routers to decide on a path through a network based on the status of the networks in between. This relieved the administrator from having to reconfigure the routers every time something changed. Suddenly, the prospect of drastic network growth and redundancy was not so frightening. Additions, deletions, modifications, and failures of networks no longer required the intervention of administrators at every network hop.