BGP flapping

[dtwoods83]

Can BGP flap becasue of an over utilized interface? If so why would it flap? Is it becasue the hold timers are timing out? 

[Georg Pauwen]

Hello,

I guess a heavily overutilized interface would drop traffic because the buffers cannot handle the amount of packets. If BGP keepalives do not make it through either, BGP would flap.

[dtwoods83]

The link was 90 to 100 percent overutilized. The core switch was doing the load balancing for both routers. I shut down the connection from the core going to the router that BGP was flapping and overutilized on. The flapping stop almost right away. I was not sure if it was coincidence or not. When I brought the connection back up the switch was load balancing correctly again and did not see any flaps. 

[Georg Pauwen · Accepted solution]

Hello,

I guess your explanation answered your own question. The overutilized interface looked to BGP like a down interface, so it was flapping...

[dtwoods83]

Thanks 

[balaji.bandi · Accepted solution]

If you do not like the BGP to flap, then reserve some bandwidth to BGP, using policy map :

you can find example :

https://community.cisco.com/t5/routing/bgp-flapping-issue-due-to-over-utilization-of-link/td-p/889873