[c-nsp] BGP Hold time expired/ospf dropping 6500 Sup720-3BXL

[Drew Weaver]

Howdy all,

Last night I had an interesting encounter on one of my 6509s /w SUP7203-BXL.

This switch has 3x iBGP sessions with full internet tables and is also running OSPF.

Two of the three iBGP sessions randomly dropped with: 

%BGP-3-NOTIFICATION: sent to neighbor x.x.x.3 4/0 (hold time expired) 0 bytes, I also noticed that during this period OSPF dropped with Neighbor Down: Dead timer expired

and then re-established, and then failed again, and re-established, and failed again, and so-on, and so-on.

I checked the physical interfaces between this 6500 and the two GSR 12000s it peers with and there were no errors, there was also no obvious spike in traffic that would account for latency that might cause the hold timers to expire. I remember when this system first came online it took a really long time for it to download the full internet tables from the upstream GSRs and also during that time there was a lot of CPU time being eaten up, I am wondering if maybe the first session failing caused sort of a 'performance' domino effect which then caused everything else to fail, the issue eventually corrected itself and stabilized.

This particular box is running 12.2(18)SXF17 so I am less likely to believe it is a software bug.

Does anyone have any tips on both how I can avoid the hold timer issue altogether and also how I can make it so that if a session does go down and re-establish it doesn't totally nail the CPU while it's trying to re-establish/download the routes? A long time ago I also read that increasing the MTU on both ends of a circuit can make BGP tables download faster, I don't know if that's true or not, has anyone else found that?

thanks,
-Drew