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

"Enke Chen (enkechen)" <enkechen@cisco.com> Thu, 01 August 2019 05:29 UTC

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From: "Enke Chen (enkechen)" <enkechen@cisco.com>
To: Jeffrey Haas <jhaas@pfrc.org>
CC: Alvaro Retana <aretana.ietf@gmail.com>, "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>, "idr-chairs@ietf.org" <idr-chairs@ietf.org>, "Enke Chen (enkechen)" <enkechen@cisco.com>
Thread-Topic: [Idr] Capability Advertisement in draft-ietf-idr-bgp-extended-messages
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Date: Thu, 1 Aug 2019 05:29:41 +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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Hi, Jeff:

1) It is a new capability, and it will take time for it to be deployed or enabled. A BGP speaker has to deal
with the case that some neighbors have advertised the capability, and some have not. That is already
covered in "Section 4 Operation" of the draft. 

2) In terms of deployment, as this feature is likely to be controlled by config (and likely "off" by default),
requiring both sides to advertise the capability simultaneously would make it difficult for the feature to
be deployed or used.

3) I do not see a reason for this capability to be different from other capabilities that do not require
bi-directional advertisement of the capability.

Thanks.  -- Enke

-----Original Message-----
From: Jeffrey Haas <jhaas@pfrc.org>;
Date: Wednesday, July 31, 2019 at 5:27 PM
To: "Enke Chen (enkechen)" <enkechen@cisco.com>;
Cc: Alvaro Retana <aretana.ietf@gmail.com>;, "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>;, "idr-chairs@ietf.org"; <idr-chairs@ietf.org>;
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, §4.1), 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