Overview of IP Unicast Routing 8-3Dynamic RoutesDynamic routes are typically learned by way of RIP. Routers using RIPexchange information in their routing tables in the form of RIPadvertisements. Using dynamic routes, the routing table contains onlynetworks that are reachable.Dynamic routes are aged out of the table when a RIP update for thenetwork is not received for a period of time.Static RoutesStatic routes are manually entered into the routing table. Static routesare used to reach networks not advertised by routers. You canconfigure up to 64 static unicast routes on the Switch 3800.Static routes can also be used for security reasons, to control whichroutes you want advertised by the router. You can decide if you wantall static routes to be advertised by using the following command:[enable | disable] rip exportstaticThe default setting is enabled. Static routes are never aged out of therouting table.Multiple RoutesWhen there are multiple, conflicting choices of a route to a particulardestination, the router picks the route with the longest matchingnetwork mask. If these are still equal, the router picks the route usingthe following criteria (in the order specified):n Directly attached network interfacesn ICMP redirects (refer to Table 8-4)n Static routesn RIPn Directly attached network interfaces that are not active.You can also configure blackhole routes—traffic to these destinationsis silently dropped.
