Re: [lisp] Rtgdir last call review of draft-ietf-lisp-gpe-04

"Adrian Farrel" <adrian@olddog.co.uk> Thu, 09 August 2018 16:39 UTC

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Reply-To: <adrian@olddog.co.uk>
From: "Adrian Farrel" <adrian@olddog.co.uk>
To: "'Dino Farinacci'" <farinacci@gmail.com>
Cc: <rtg-dir@ietf.org>, <draft-ietf-lisp-gpe.all@ietf.org>, <lisp@ietf.org>, <ietf@ietf.org>
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Date: Thu, 9 Aug 2018 17:39:01 +0100
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Archived-At: <https://mailarchive.ietf.org/arch/msg/lisp/a6X0LQB6xfQQCT5U2aN_PIkbsQA>
Subject: Re: [lisp] Rtgdir last call review of draft-ietf-lisp-gpe-04
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Hello Dino,

> > No attempt is made in the document to explain how/why the reduction in size
> > of some standard LISP header fields is acceptable. For example, if
> > implementations of this spec can safely operate with a 16 bit Nonce or 8 bit
> > Map-Versions, why does 6830/6830bis feel the need for 24 and 12 bit fields
> > rspectively?
> 
> Note, you misread RFC6830. The Map-Version field is 24-bits when the V bit is
> set. And is divided up like this:
> 
>     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
>     |N|L|E|V|I|flags|  Source Map-Version   |   Dest Map-Version    |
>     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
>     |                 Instance ID/Locator-Status-Bits               |
>     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

I don't think I missed that even slightly.
The Map-Version field is 24 bits and split into two 12 bit Map-Versions (source
and dest).
When the P-bit is set, the Map-Version is reduced to 16 bits and is (presumably)
split at 8 bits each for source and dest (see my new text).

So my question could be seen as:
Why does this document only need 8 bits for Source Map-Version when 6830 needed
12 bits?

Cheers,
Adrian