Question about normal ops - BGP Flaps nightly

Fri Nov 22 04:48:34 UTC 2019

On Fri, Nov 22, 2019 at 12:40 PM Christopher Morrow
<morrowc.lists at gmail.com> wrote:
>
> On Fri, Nov 22, 2019 at 12:32 PM Baldur Norddahl
> <baldur.norddahl at gmail.com> wrote:
> >
> >
> >
> > 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 When the BGP session flaps your routes via that provider are withdrawn.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 When the active route is withdrawn ISP B will momentary be without any route to your network.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.
>
> Yup, I'm sensitive to flapping causing problems. This was why i
> started the thread, which really should have been:
>   "Is there a well known bug people are working around? or is this a
> new problem I should chase with the provider? or 'nah, everyone does
> this, you just aren't normally paying attention'"
>
> >
> > 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.
> >
>
> fortunately 3am local time is not prime-internet-use time :) phew!
> (not a great excuse though, of course)
>

The other saving grace / "meh" is that this is for a conference
network, and we are picking up sticks and leaving tomorrow... so, we
will let the provider know that there is something that should be
fixed, but a: our pain will have stopped :-P and b: we won't really
have a good way to know if they have fixed the issue (other than
perhaps watching for a spike of withdraws / reannouncements every 24
hours through this AS path)

W

> I'll be chasing up the provider to see what's up.
> thanks!
> -chris
>
> > Regards,
> >
> > Baldur
> >

-- 
I don't think the execution is relevant when it was obviously a bad
idea in the first place.
This is like putting rabid weasels in your pants, and later expressing
regret at having chosen those particular rabid weasels and that pair
of pants.
   ---maf