Re: [Idr] IETF LC for IDR-ish document <draft-ietf-grow-bgp-reject-05.txt> (Default EBGP Route Propagation Behavior Without Policies) to Proposed Standard

Mikael Abrahamsson <swmike@swm.pp.se> Wed, 26 April 2017 11:40 UTC

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Date: Wed, 26 Apr 2017 13:40:01 +0200 (CEST)
From: Mikael Abrahamsson <swmike@swm.pp.se>
To: Robert Raszuk <robert@raszuk.net>
cc: Gert Doering <gert@space.net>, idr wg <idr@ietf.org>
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Subject: Re: [Idr] IETF LC for IDR-ish document <draft-ietf-grow-bgp-reject-05.txt> (Default EBGP Route Propagation Behavior Without Policies) to Proposed Standard
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On Wed, 26 Apr 2017, Robert Raszuk wrote:

> Hi Gert,
>
> Unless the result is not lost of connectivity but lost of BGP path
> redundancy from your AS.
>
> It is quite often and in fact good idea to have dual vendors as your ASBRs.
>
> So unless proper cli is automagically added the problem may only  surface
> weeks and months after upgrade and in fact far from given ASBR when
> external link from still operational ASBR breaks.
>
> Document should discuss that as well and recommend such auto cli.

Let me just understand the reasoning here:

Operator today deploys ASBR without neighbor policy. It sends all routes 
to peer/transit and accepts all routes. This is not noticed by other end 
maximum-prefix and they have filtering in place to drop the "erraneous 
prefixes", so everything is working fine.

Now the router is rebooted with new version of software, that is 
default-deny, and vendor didn't provide CLI parser to migrate config to 
assure consistent behaviour in the new version. After the reboot, all 
routes are denied in/out. Operator doesn't check this now unused link, so 
this state is prolonged for an extended amount of time, all traffic is 
traversing other path, only. Still nobody notices.

Now other link goes down for some reason. Now these ASNs are isolated from 
each other, because there is no backup over transit for some reason, or 
transit becomes congested.

This is the scenario you want analyzed? Or is the scenario you want to 
protect against more non-Internet related, no DFZ amount of routes etc?

Because I find the behaviour I describe above as implausible for any 
decently professionally run network.

-- 
Mikael Abrahamsson    email: swmike@swm.pp.se