Re: [Gen-art] Review of draft-ietf-6man-rfc1981bis-04

Joe Touch <touch@isi.edu> Thu, 16 February 2017 18:50 UTC

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Subject: Re: [Gen-art] Review of draft-ietf-6man-rfc1981bis-04
To: Stewart Bryant <stewart.bryant@gmail.com>, "Templin, Fred L" <Fred.L.Templin@boeing.com>, Brian E Carpenter <brian.e.carpenter@gmail.com>, "gen-art@ietf.org" <gen-art@ietf.org>
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From: Joe Touch <touch@isi.edu>
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Date: Thu, 16 Feb 2017 10:49:58 -0800
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On 2/16/2017 7:59 AM, Stewart Bryant wrote:
>
>
> On 14/02/2017 23:00, Templin, Fred L wrote:
>> Unless there is operational assurance of
>> some size X>1280, however, tunnels have to use fragmentation to
>> guarantee that - at a minimum - packets up to 1280 will get through.
>
> In that case there really needs to be a note about MPLS.

IMO, this doc shouldn't be discussing tunneling as any different from
any other link.

> You can fragment into an IP tunnel, but not an MPLS tunnel, because
> you cannot fragment the payload as you can in IPv4 and you cannot
> fragment MPLS.

There's no such thing as an "MPLS tunnel"; at best, it's "MPLS over X",
e.g., MPLS over ethernet. MPLS doesn't indicate a message length so
while it can't support fragmentation it would never need it either. It
would be the next layer down (e.g., Ethernet, ATM, etc.) that might have
needed fragmentation.  If that can't be supported, then the addition of
MPLS would just reduce the effective MTU of the MPLS-over-X link.

Joe