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> Wed, 01 June 2016 10:51 UTC

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To: Nick Hilliard <nick@foobar.org>
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: Wed, 01 Jun 2016 12:51:02 +0200
From: Marco Marzetti <marco@lamehost.it>
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On 2016-05-31 17:40, Nick Hilliard wrote:
> Marco Marzetti wrote:
>> 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.
> 
> It doesn't "break" the decision process mechanism.  Localpref might be
> ugly, but using it doesn't violate the bgp protocol.
> 
> This statement needs to be "MUST NOT".  Technically you can run a route
> server even if you insert the intermediate ASN into the path.  The only
> absolute "MUST" is that you mustn't change the next-hop; otherwise you
> end up with a router instead of a route server.
> 
> RFC2119 is a pain because there is no way of differentiating between
> "SHOULD NOT", meaning "on balance it would be a better idea not to do 
> X"
> and "SHOULD NOT", meaning "if you even _think_ about doing X, you need
> your head examined and the only reason we specified SHOULD NOT instead
> of MUST NOT in this situation because of some technicality that
> prevented us from doing so".  The text in 2.2.2 veers slightly in the
> direction of the latter interpretation.
> 
> Nick

Nick,

I agree with you that you can run a route server and insert your ASn in 
the path, but i think that is a lack of common sense which brings only 
contraries and no benefits.

About RFC2119: It says that "SHOULD NOT" implies a valid reason to 
accept a behavior, but i can't find any.

Regards

-- 
Marco