Chapter 2. Routing Metrics and Distances

This chapter focuses on convergence and parallel paths, primarily discussing their interaction with routing metrics and distances.

Convergence is the process routers go through when a route (network) or group of routes has become unavailable due to a link going down in the network or extreme packet loss on a link. This loss results in the routers flushing the lost routes and listening to see whether other routes are available. Routers usually store only the best route to a network in their routing tables. Other, higher-cost, routes may exist, but the router ignores them if it believes that the better route still exists.

In the example in Figure 2-1, RouterA converges on a new path to 168.71.8.1 because the link between RouterA and RouterC has failed.