[nsp] BGP Dampening bug?

From: Rick Payne (rickp@rossfell.co.uk)
Date: Thu Oct 19 2000 - 12:41:17 EDT


We've been running with the RIPE specified values on BGP dampening for a
while now. However - I noticed an oddity today when debugging zebra.

A route which was flapping was getting to its supress value, but never
going above it. This meant the route was withdrawn but almost immediately
re-instated with no hold down. It turns out that this is because we had the
supress value as a multiple of the half life.

We had:

 route-map graded-flap-damping permit 20
  match ip address prefix-list min24
  set damp 30 750 3000 60

This caused oscillations inside our mesh - because the route was never
getting held down.

Once we changed it to

 route-map graded-flap-damping permit 20
  match ip address prefix-list min24
  set damp 30 750 3001 60

Then the route got held down properly.

Is this a bug in our understanding? or the code. I guess that as RIPE
specify this - there will be lots of people using it.

Rick



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