Question about normal ops - BGP Flaps nightly

Fri Nov 22 04:32:24 UTC 2019

On Fri, Nov 22, 2019 at 1:21 AM Christopher Morrow <morrowc.lists at gmail.com>
wrote:

> On Fri, Nov 22, 2019 at 2:01 AM Saku Ytti <saku at ytti.fi> wrote:
> >
> > On Thu, 21 Nov 2019 at 19:44, Baldur Norddahl <baldur.norddahl at gmail.com>
> wrote:
> >
> > > A BGP reset can cause routing trouble for as much as 15 minutes. Since
> you have two sessions that mitigates the problem somewhat. But nevertheless
> this will not be acceptable.
> >
> > As there are best path algorithms which consider route age, BGP reset
> > impact may be indefinite.
>
> fortunately we have a second actual provider... so this all isn't
> super impacting to us, just weird and unexpected on my part.
>
>
No that is not helping. When the BGP session flaps your routes via that
provider are withdrawn. Everyone out there that were using those routes
will need to switch. But consider the following:

ISP A has routes from both of your providers
ISP B has A as uplink

BGP works so that ISP A is only announcing the route that he is actually
using to ISP B. ISP B therefore does not have both of your routes. When the
active route is withdrawn ISP B will momentary be without any route to your
network. It can take some time after the withdraw before ISP A announces
that he now is using the alternative route. This gets worse with longer
chains. Also some ISPs are using route flap limiting techniques that can
prolong this process.

As I said, my experience is that you can expect as much as 15 minutes of
flaky internet after a BGP reset. This is with multiple transit providers.

I can not say too much about why you have BGP resets, but I can say that
you really want it fixed. It will affect your connectivity.

Regards,

Baldur
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