Newbie Concern: (BGP) AS-Path Oscillation

Mon Nov 28 09:03:52 UTC 2022

On Sun, Nov 27, 2022 at 9:52 PM Pirawat WATANAPONGSE via NANOG
<nanog at nanog.org> wrote:
> On one of our prefixes, we are detecting continuous “BGP AS-Path Changes” in the order of 1,000 announcements per hour---practically one every 3-4 seconds.
> Those paths oscillate between two of our immediate upstreams.

Hi Pirawat,

What are they changing -from- and what are they changing -to-? I.e.
what are the actual RIB entries in your routing table. Not merely the
selected one, but all of the RIB entries known to your router for that
route at each stage of the oscillation.

It's hard to say whose bug it is without digging a little deeper. It
might be your bug. It's also hard to say whether the fault is
user-impacting without doing that sort of basic diagnosis.

> 2. Is there any way we, as the tail-end (Origin Announcer), can do to reduce it?

BGP route flap damping, sometimes incorrectly called route dampening
if you're trying to search for it.

Regards,
Bill Herrin

-- 
For hire. https://bill.herrin.us/resume/