Re: [Idr] Last Call: <draft-ietf-idr-ix-bgp-route-server-10.txt> (Internet Exchange BGP Route Server) to Proposed Standard

Marco Marzetti <marco@lamehost.it> Fri, 27 May 2016 10:08 UTC

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To: Greg Skinner <gregskinner0@icloud.com>
Subject: Re: [Idr] Last Call: <draft-ietf-idr-ix-bgp-route-server-10.txt> (Internet Exchange BGP Route Server) to Proposed Standard
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Date: Fri, 27 May 2016 12:08:08 +0200
From: Marco Marzetti <marco@lamehost.it>
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On 2016-05-27 08:59, Greg Skinner wrote:
>> On May 25, 2016, at 6:11 AM, Marco Marzetti <marco@lamehost.it>;
>> wrote:
>> 
>> On 2016-05-25 00:43, The IESG wrote:
>> 
>>> The IESG has received a request from the Inter-Domain Routing WG
>>> (idr) to
>>> consider the following document:
>>> - 'Internet Exchange BGP Route Server'
>>> <draft-ietf-idr-ix-bgp-route-server-10.txt> as Proposed Standard
>>> The IESG plans to make a decision in the next few weeks, and
>>> solicits
>>> final comments on this action. Please send substantive comments to
>>> the
>>> ietf@ietf.org mailing lists by 2016-06-07. Exceptionally, comments
>>> may be
>>> sent to iesg@ietf.org instead. In either case, please retain the
>>> beginning of the Subject line to allow automated sorting.
>>> Abstract
>>> This document outlines a specification for multilateral
>>> interconnections at Internet exchange points (IXPs).
>>> Multilateral
>>> interconnection is a method of exchanging routing information
>>> between
>>> three or more external BGP speakers using a single intermediate
>>> broker system, referred to as a route server.  Route servers are
>>> typically used on shared access media networks, such as Internet
>>> exchange points (IXPs), to facilitate simplified interconnection
>>> between multiple Internet routers.
>>> The file can be obtained via
>>> 
>> https://datatracker.ietf.org/doc/draft-ietf-idr-ix-bgp-route-server/
>>> IESG discussion can be tracked via
>>> 
>> 
> https://datatracker.ietf.org/doc/draft-ietf-idr-ix-bgp-route-server/ballot/
>>> No IPR declarations have been submitted directly on this I-D.
>>> _______________________________________________
>>> Idr mailing list
>>> Idr@ietf.org
>>> https://www.ietf.org/mailman/listinfo/idr
>> 
>> All,
>> 
>> Beside i agree on the most part of this draft i would like to
>> underline how bullet 2.2.2 breaks the the nature of BGP itself.
>> 
>> The exact part i am referring to is:
>> """
>> As a route server does not participate in the process of forwarding
>> data between client routers, and because modification of the
>> AS_PATH
>> attribute could affect route server client BGP Decision Process,
>> the
>> route server SHOULD NOT prepend its own AS number to the AS_PATH
>> segment nor modify the AS_PATH segment in any other way.
>> """
>> 
>> I firmly think that it really has to state "MUST NOT" instead of
>> "SHOULD NOT".
>> 
>> From a route-server client point of view that breaks the natural BGP
>> best selection process and forces you to purely rely on
>> LOCAL_PREFERENCE which in turns breaks your traffic engineering
>> because it forces you to prefer/not-prefer the prefixes learned over
>> the route server in place of those learned, for instance, over a
>> private session or another IXP.
>> 
>> Regards
>> 
>> --
>> Marco
>  Marco,
> 
> There are some IXP route servers that prepend their AS number to the
> AS_PATH, according to some things I’ve read, such as this Akamai
> presentation [1].  My guess is the use of “SHOULD NOT” here
> reflects that this is not a recommended procedure.
> 
> Since your concerns about traffic engineering are operational in
> nature, perhaps you could address them via
> draft-ietf-grow-ix-bgp-route-server-operations.
> 
> Incidentally, idnits turned up an outdated reference: a later version
> (-15) exists of
> draft-ietf-idr-add-paths-13.
> 
> —gregbo
> 
> 
> 
> Links:
> ------
> [1] http://peeringforum.bknix.co.th/2016/docs/Bob%20Lau%20(Akamai).pdf

Dear Greg,

I have had private chats with Niels and Nick before i submitted my rant 
and i understand their reasons, but i really don't agree with them.
In fact I think that the community should firmly discourage that 
practice.


About draft-ietf-grow-ix-bgp-route-server-operations: this is the 
relevant excerpt:
"""
    As [I-D.ietf-idr-ix-bgp-route-server] suggests that route servers
    should not modify the AS_PATH attribute, a consistency check on the
    AS_PATH of an BGP route received by a route server client would
    normally fail.  It is therefore RECOMMENDED that route server clients
    disable the AS_PATH consistency check towards the route server.
"""

The words "RECOMMEND" and "SHOULD" imply that there could be a valid 
reason, but i can't find any.
Now, we may address that in this draft only, but it would lack common 
sense because the theory would let room to a practice that is denied in 
the operations.

Regards


-- 
Marco