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

Brian E Carpenter <brian.e.carpenter@gmail.com> Thu, 16 February 2017 19:59 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>, "gen-art@ietf.org" <gen-art@ietf.org>
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From: Brian E Carpenter <brian.e.carpenter@gmail.com>
Organization: University of Auckland
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Date: Fri, 17 Feb 2017 08:59:15 +1300
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On 17/02/2017 04:59, 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.
> 
> 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.

I'm confused. A tunnel end point that accepts IPv6 packets MUST accept packets
of 1280 bytes (or shorter) and MUST emit them. How it gets them through the
tunnel is irrelevant - if it's an ATM tunnel it has to chop them into 48 byte
fragments and re-assemble them at the other end - if it's an avian carrier tunnel
it might have to use several pigeons per packet*. None of this matters to the IPv6
nodes concerned; the physical MTU of the tunnel technology is irrelevant except
to the tunnel end points.

   Brian

*In RFC 6214, we didn't consider this, but we should have.