Re: [Idr] Early allocation for draft-ietf-idr-bgp-gr-notification

Job Snijders <job@ntt.net> Tue, 21 March 2017 15:28 UTC

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Date: Tue, 21 Mar 2017 16:28:31 +0100
From: Job Snijders <job@ntt.net>
To: "John G. Scudder" <jgs@juniper.net>
Cc: Jeffrey Haas <jhaas@pfrc.org>, "idr-chairs@ietf.org" <idr-chairs@ietf.org>, "idr@ietf.org" <idr@ietf.org>
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Subject: Re: [Idr] Early allocation for draft-ietf-idr-bgp-gr-notification
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On Mon, Mar 20, 2017 at 05:49:50PM -0400, John G. Scudder wrote:
> On Mar 20, 2017, at 4:41 PM, Jeffrey Haas <jhaas@pfrc.org> wrote:
> > On Mon, Mar 20, 2017 at 09:14:55PM +0100, Job Snijders wrote:
> > [session culling]
> >>> I haven't yet read this draft, so take my further comments with that under
> >>> consideration.
> >> 
> >> ack. Please read the draft. We may have a fundamental problem on our
> >> hands here.
> > 
> > I read it. It's a weird hack, but it works. :-)
> 
> With respect to what "culling" calls "Involuntary BGP Session
> Teardown", there is potentially a problem, but I think it's not
> insurmountable. The problem, to the extent it exists, is that
> "culling" suggests the IX switch fabric should be configured to block
> BGP traffic, causing the hold time to expire. gr-notification
> interferes by putting the session into GR mode:
> 
>    When a BGP speaker resets its session due to a HOLDTIME expiry, it
>    should generate the relevant BGP NOTIFICATION message as mentioned in
>    [RFC4271], but subsequently it MUST follow the rules for the
>    Receiving Speaker mentioned in Section 4.1.
> 
> At first this might seem alarming, but my observation is that the
> weird hack already relies on waiting several minutes for the hold time
> to expire. So, it doesn't seem terrible to add a few more minutes to
> wait for the stale route timeout as well.

Your analysis is helpful. We might add a note to the bgp-culling draft
that "GR Notification" could negatively affect with the minimum required
bgp culling time spam.

> Although "culling" doesn't discuss how to determine the maintenance
> can proceed, it would seem both prudent and straightforward to do so
> by monitoring the traffic level between the affected peers, since
> presumably the IX operator doesn't have a priori knowledge of the hold
> time in use. Once routing has converged away from the path, the
> traffic level will drop, and the maintenance can proceed, regardless
> of what perversions are in use in the control plane. 

Correct.

Kind regards,

Job