BGP route flapping

Wed May 14 21:39:35 UTC 2014

On Wed, 14 May 2014, Gus Crichton wrote:

> Hope you networking experts can shed some light on a concern I have 
> please. I am multihoming using 2 ISPs to the internet, due to reasons 
> outside my control, my primary preferred link keeps dropping a number of 
> times a day forcing traffic to my backup and vice-versa when the primary 
> comes back up.

Is it feasible to make your backup ISP your primary ISP until your 'real' 
primary ISP gets the link flapping issues sorted out, or you and your real 
primary ISP work together to get the issue sorted out?

> The route calculations by the upstream tier 1s and 2s handle the route 
> calculations but if I do this too many times consuming their resources, 
> is there a penalty/blackmark on my AS? Is this monitored even by the 
> tier1s and 2s?

Networks can choose to implement some amount of BGP flap damping, however 
this is generally done at the closest point to the source of the flapping.

This is typically a temporary measure - the damped routes will be restored 
after a period of stability.

The bigger issue is finding the source of the flapping and getting it 
fixed.

jms