Re: [Idr] Capability Advertisement in draft-ietf-idr-bgp-extended-messages

"Jakob Heitz (jheitz)" <jheitz@cisco.com> Thu, 01 August 2019 05:04 UTC

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From: "Jakob Heitz (jheitz)" <jheitz@cisco.com>
To: Jeffrey Haas <jhaas@pfrc.org>, "Enke Chen (enkechen)" <enkechen@cisco.com>
CC: "idr-chairs@ietf.org" <idr-chairs@ietf.org>, "idr@ietf. org" <idr@ietf.org>, "draft-ietf-idr-bgp-extended-messages@ietf.org" <draft-ietf-idr-bgp-extended-messages@ietf.org>, Susan Hares <shares@ndzh.com>
Thread-Topic: [Idr] Capability Advertisement in draft-ietf-idr-bgp-extended-messages
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Date: Thu, 1 Aug 2019 05:04:37 +0000
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References: <CAMMESsyvuU8_dBOeoOXPBt=-HwoF0eHvYgm5d8CgF-4o_oiP=g@mail.gmail.com> <20190731211602.GA31271@pfrc.org> <119404A5-8384-456B-9677-0445899B008F@cisco.com> <20190801002911.GB31271@pfrc.org>
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Subject: Re: [Idr] Capability Advertisement in draft-ietf-idr-bgp-extended-messages
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I'll raise you one.
A single speaker in a network that is not capable of receiving extended
messages will lead to a mess of (non-edge) cases. 

How about:

A BGP speaker MUST NOT send the extended messages capability in
an OPEN message to any BGP speaker if it has received an OPEN message
without the extended message capability from any
BGP speaker. A BGP speaker MUST delay sending an OPEN message to
any BGP speaker by one keepalive interval if that OPEN message will
contain the extended message capability and it has not yet received
an OPEN message from every configured BGP speaker. The stated OPEN
messages are understood to be of current or future BGP sessions,
not of old sessions that have been taken down.

This will reduce, but not completely eliminate the mess cases.

Regards,
Jakob.

-----Original Message-----
From: Idr <idr-bounces@ietf.org>; On Behalf Of Jeffrey Haas
Sent: Wednesday, July 31, 2019 5:29 PM
To: Enke Chen (enkechen) <enkechen@cisco.com>;
Cc: idr-chairs@ietf.org; idr@ietf. org <idr@ietf.org>;; draft-ietf-idr-bgp-extended-messages@ietf.org; Susan Hares <shares@ndzh.com>;
Subject: Re: [Idr] Capability Advertisement in draft-ietf-idr-bgp-extended-messages

Enke,

On Wed, Jul 31, 2019 at 09:50:08PM +0000, Enke Chen (enkechen) wrote:
> >>  Note that RFC 6793 (4-byte ASes) require bi-directional advertisement.
> 
> No, this statement is not correct. It is fundamental (in transition) for a BGP  speaker
> to be able to talk to both NEW speakers (that have advertised the capability), and OLD
> speakers (that have not advertised the capability).  Different encodings are used in the
> UPDATE message depending on whether the 4-byte AS capability is received from a
> neighbor.

I should have known I wasn't pedantic enough in this comment. :-)

The point here is that in order to exercise the procedures between NEW BGP
speakers, (RFC 6793, ยง4.1), both sides must advertise and use the
capability.  If you have a mix, each speaks 4271 to each other with the new
speaker running the transitional procedures.

With regard to the extended messaging, my preference is that both sides
advertise the capability in order to use the large messages.  A mis-match
falling back to 4271 4k PDUs is fine - symmetrically.  Asymmetrically
sending extended messages leads to a mess of edge cases.

-- Jeff

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