Saturday, November 3, 2018

6500 IOS 12.2 - Sup720 failover - Lost BGP Peers?

So I was doing some routine maintenance on a non-critical system and I was doing a force failover of the Sup720 engines. This 6500 has its BGP peers on a separate line card (i.e. not using the Sup's built-in interfaces).

I had a remote host pinging the router, then I did the failover. Everything appeared to be fine, then I noticed my remote ping died, and I also noticed "sh ip bgp summ" showed my two BGP sessions were down, and in the process of re-establishing. After 30 secs or so the sessions were back up, and my remote ping resumed.

This was a surprise because I assumed when running SSO redundancy (Active/Hot) a Sup failover causes zero interruption. Why then did the BGP sessions go down? It was a 30 second outage, not a big deal, but I was expecting zero downtime.

-John



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