On Wed, May 01, 2013 at 08:56:32PM +0300, Dan Shechter wrote: > You can't filter OSPF routes inside an area. It will break the OSPF > shortest path tree. > > I don't know about ospfd, but on Cisco IOS you can filter routes > (LSAs) between areas and you can also prevent prefixes from being > inserted to the routing table of the router where the filtering > commands are entered (you can't influence other routers' decisions for > intra area routes) . >
Not having routes from the LSDB (RIB) in the routing table (FIB) is a good way to melt down your network with routing loops. In OSPF there is the assumption that if there is a path in the link-state DB passing router A-B-C that the traffic will also flow that way. This is only possible if the FIB and the RIB are in sync. You can't use a link-state routing protocol with a distributed DB when you want to filter. Sure we could add inter-area filtering but even there you may end up with some strange behaviours. The somewhat big hammer is to use a stub area in that case. Until now I never saw a good reason for complex filter logic and so I never implemented it. -- :wq Claudio
