Posted by Aragoen Celtdra on August 1st, 2011
While going through some BGP examples in Routing TCP/IP Volume II, I came across an issue where RIB failures continue to pop up in the show commands. To illustrate see the following topology I recreated from the book (pg 175, fig 3-6 on Routing TCP/IP II book)
Telluride is advertising prefixes 192.168.1.200/30, 192.168.50.0, and 192.168.75.0 via IBGP towards Vail. Vail, however, is also learning these same routes via OSPF through Aspen. As shown in the sh ip route output for one of the routes above, an OSPF advertisement has an AD of 110, whereas an IBGP advertisement has an AD of 200. Even though the routes are in Vail’s BGP table, the OSPF route is installed in the routing table because of lower administrative distance. BGP then throws a fit because he has the routes in his table and the router ignored him.
This is normal operation for BGP. In fact, even though Vail does not use the route via BGP it is not suppressed or thrown out. If you check the ip routing table in Taos, you’ll see that BGP is sending these same routes from Vail. So at least BGP is happy there