Re: [sfc] NSH MD-1 description

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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