[c-nsp] ospf nssa ibgp problem

[Bruce Pinsky]

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Jon Lewis wrote:
> 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.  After a short 
> time, the 7206 repopulates the routing table with the ~200K BGP routes, 
> but then 30-40s later, it purges the table again.  The 7206 is running 
> c7200-k91p-mz.122-18.S12.bin.
> 
> Making it a regular NSSA area by removing 'no-redistribution no-summary' 
> from the 7600 makes no difference with this issue.  If I get rid of the 
> NSSA area and put the 7206 into area 0, the routes load (and stay loaded) 
> as expected.
> 
> Is this a BGP bug in 122-18.S12, or do NSSA and iBGP just not get along 
> for some reason?

So the 7206 is in the NSSA and receiving routes from an RR that is in area
0?  If that is the case, how will the 7206 learn the nexthops for the BGP
routes since the ABR will only be generating default into the NSSA?  It
would explain the oscillating behavior since every 60 seconds bestpath
would run and find that there is not an explicit route to the nexthops.

- --
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bep

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