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Re: [sfc] NSH MD-1 description

"Jim Guichard (jguichar)" <jguichar@cisco.com> Fri, 04 November 2016 20:25 UTC

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From: "Jim Guichard (jguichar)" <jguichar@cisco.com>
To: "sarikaya@ieee.org" <sarikaya@ieee.org>, "Joel M. Halpern" <jmh@joelhalpern.com>
Thread-Topic: [sfc] NSH MD-1 description
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Date: Fri, 04 Nov 2016 20:25:16 +0000
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Cc: "sfc@ietf.org" <sfc@ietf.org>
Subject: Re: [sfc] NSH MD-1 description
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Hi Behcet,

Please see my earlier email and https://trac.tools.ietf.org/wg/sfc/trac/ticket/22 where rough consensus has been reached to change the 4 contexts to a single 16-byte fixed context header. This change will be reflected in the next revision of the NSH document.

Jim




On 11/4/16, 4:13 PM, "sfc on behalf of Behcet Sarikaya" <sfc-bounces@ietf.org on behalf of sarikaya2012@gmail.com> wrote:

>I think that definitely some action is needed on the definition of
>metadata Type 1
>
>draft-ietf-sfc-nsh-10
>
>I have never been able to figure out why
>
>four Context Headers,
>   4-byte each, MUST be added immediately following the Service Path Header.
>
>What is the role of the number 4? It has not been explained in the document.
>
>Different use cases have different requirements and I have not seen 4
>MD Type 1 defined in a sensible manner for each use case that we know
>so far. There is a proposal for the data center use case in
>draft-guichard which contains exactly 4 data types. That seems to be
>about it.
>
>For the mobility use there is a proposal but it defines 3 data not 4.
>
>I don't understand why this point waited so long (until Rev. 11) to get fixed?
>
>I think fixing it is not going to be easy, it should have been
>addressed much earlier.
>
>Regards
>
>Behcet
>
>
>On Wed, Nov 2, 2016 at 12:57 PM, Joel M. Halpern <jmh@joelhalpern.com> wrote:
>> <speaking as a participant>
>> Given that various existing MD-1 proposals break up the "4" fields in
>> various ways, and given that we may want to allow , for example, a singl 64
>> bit field in some MD-1 allocation, it seems cleaner and more consistent to
>> me to describe the MD-1 content as a block of 16 bytes rather than as 4 4
>> byte words.
>>
>> Given that this is purely descriptive for the NSH document, I do not see a
>> down side.  YANG models for metadata are a more complex question, but the
>> simple 4x4 byte representation is probably not want we want there either.
>>
>> Yours,
>> Joel
>>
>> </speaking as a participant>
>>
>> _______________________________________________
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>> sfc@ietf.org
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>
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