[c-nsp] ospf nssa ibgp problem

[Oliver Boehmer (oboehmer)]

cisco-nsp-bounces at puck.nether.net <> wrote on Monday, October 16, 2006
8:13 PM:

> I just tried setting up an NSSA area and had a strange issue with BGP
> routes.  The routers involved are a 7600 in area 0 and area 152, and a
> 7206vxr in area 152.
> 
> On the 7600, I configured the NSSA area as:
>   area 152 nssa no-redistribution no-summary
> 
> On the 7206, it's just:
>   area 152 nssa
> 
> For some reason, iBGP (trying to send the 7206 full routes
> from a pair of
> 7600's acting as route-reflectors) even with no synch on the 7206
> isn't working properly.  The 7206 receives ~200K routes, loads them
> into the routing table (seen via show ip route sum), but then after
> less than a minute, it flushes the BGP routes from the routing table.
The BGP
> sessions remain up, and report ~200K routes received. 

Sounds like the classical "BGP resolves the BGP next-hop through a BGP
prefix" symptom. Make sure you have a specific OSPF route to your
next-hop in the routing table. Make sure you configure "next-hop-self"
on all your edge routers towards the RR. This could be the issue if the
next-hop for theses "flapping" prefixes is known via an external OSPF
route (redistribute connected), and this prefix won't be sent into
NSSA..

	oli