BGP Flapping after upgrading 7600-SUP720 to 12.2(33)SRD8

[pavlosd]

Hi all,

We have a Cisco 7600 Router with SUP720/MFSC3 that was running version 12.3(33)-SRC3 for more than 2 years now. We recently had to upgrade to a newer release to solve a bug issue after recommendations, so we chose to go to SRD8 release.

Since then we are facing a rather strange problem with one of my peer ebpg. we have 2-3 peering on the same router. only one of them is affected. The ebp keeps flapping every 3 minutes due to hold down timers.

12:14:33: %BGP-5-ADJCHANGE: neighbor 15.14.11.18 Down BGP Notification sent

12:14:33: %BGP-3-NOTIFICATION: sent to neighbor 15.14.11.18 4/0 (hold time expired) 0 bytes

12:14:33: %BGP_SESSION-5-ADJCHANGE: neighbor 15.14.11.18 IPv4 Unicast topology base removed from session  BGP Notification sent

12:14:47: %BGP-5-ADJCHANGE: neighbor 15.14.11.18 Up

12:17:48: %BGP-5-ADJCHANGE: neighbor 15.14.11.18 Down BGP Notification sent

12:17:48: %BGP-3-NOTIFICATION: sent to neighbor 15.14.11.18 4/0 (hold time expired) 0 bytes

12:17:48: %BGP_SESSION-5-ADJCHANGE: neighbor 15.14.11.18 IPv4 Unicast topology base removed from session  BGP Notification sent

12:17:55: %BGP-5-ADJCHANGE: neighbor 15.14.11.18 Up 12:14:33: %BGP-5-ADJCHANGE: neighbor 15.14.11.18 Down BGP Notification sent
12:14:33: %BGP-3-NOTIFICATION: sent to neighbor 15.14.11.18 4/0 (hold time expired) 0 bytes
12:14:33: %BGP_SESSION-5-ADJCHANGE: neighbor 15.14.11.18 IPv4 Unicast topology base removed from session  BGP Notification sent
12:14:47: %BGP-5-ADJCHANGE: neighbor 15.14.11.18 Up
12:17:48: %BGP-5-ADJCHANGE: neighbor 15.14.11.18 Down BGP Notification sent
12:17:48: %BGP-3-NOTIFICATION: sent to neighbor 15.14.11.18 4/0 (hold time expired) 0 bytes
12:17:48: %BGP_SESSION-5-ADJCHANGE: neighbor 15.14.11.18 IPv4 Unicast topology base removed from session  BGP Notification sent
12:17:55: %BGP-5-ADJCHANGE: neighbor 15.14.11.18 Up

We asked our peer if they have similar problems but it seems they do not. Our peer is using Cisco 12810 running  12.0(32)SY11

After downgrading back to version 12.2(33)SRC3 again, the probem was fixed...

Any ideas?

[stephen.stack]

Have you checked the cisco bug toolkit for any bgp issues with your upgraded rev of code? Also, any config or interface differences with the one peer that keeps flapping after the upgrade? Please share them If there are..

Regards

Stephen
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[Raju Sekharan]

Hi

BGP flapping every 3 minutes with hold-timer expired means that this router didn't receive keep-alive from the neighbor within the hold-down time of 3 minutes and did reset the neighbor. Most of the cases this is an MTU issue. You need to see if there was any MTU difference on the interface or the MSS negotiated by BGP when you upgraded to SRD8.  Also check what is the current MSS negotiated by the neighbor using the command

On the peer router

show ip bgp nei  < IP address>

Thanks

Raju