[c-nsp] BGP neighbor not establishing session

[Lobo]

Well, we upgraded from 7206VXR NPEG1s to 7301 but the software went from 
12.3(26) to 12.2(33)SRE1 as well.

The interfaces on both sides are all set to 9216 mtu but the path 
between them is a lot less than that.  Another thing that a colleague of 
mine pointed out was that the distance between these routers might be 
something to look at.  The latency is around 85ms.

So even with the stuff above, it all seems to work with the older IOS 
version but not the newer.

BTW, our routers are setup in a full ibgp mesh somewhat like this but 
with a crisscross as well:

vanc-router1 -------------- toro-router1
      |                           |
      |                           |
vanc-router2 -------------- toro-router2

The vanc routers are running 12.3(33)SRE1.  They can establish an ibgp 
session to each other with no problem.  Same thing for the toro 
routers.  It was only the ibgp sessions from vanc to toro that were not 
coming up.  Now that I've downgraded toro-router1 to 12.3(26), it has 
established the sessions to vanc-router1 & 2.

Jose


On 11/22/2010 12:39 PM, Oliver Boehmer (oboehmer) wrote:
>
>> I've tried searching around for this problem but haven't found much
> info.
>> We upgraded some 7301 routers the other night
> to which software?
>
>> and there are a couple of
>> neighbors which have not been able to re-establish themselves.
>> Debugging from one of the routers shows this:
>>
>> Nov 21 21:06:51.902 EST: BGP: Neighbor validation failed. Flags: 0x10,
>> Neighbor-topo check: passed, Router ID: 172.29.1.1
>> frorr01#
>> Nov 21 21:07:00.098 EST: BGP: Neighbor validation failed. Flags: 0x10,
>> Neighbor-topo check: passed, Router ID: 172.29.1.1
>> frorr01#
>> Nov 21 21:07:10.482 EST: BGP: Neighbor validation failed. Flags: 0x10,
>> Neighbor-topo check: passed, Router ID: 172.29.1.1
>> frorr01#
>
> we've seen this once in an environment where the path/interface MTU
> didn't match.. can you check the MTU on the interface(s) and the MSS
> negotiated? TCP transaction debug might help..
>
> 	oli