Subject: Re: [Gen-art] Review of draft-ietf-6man-rfc1981bis-04
From: Brian E Carpenter <[email-masked]>
To: Stewart Bryant <[email-masked]>, "Templin, Fred L" <[email-masked]>, "[email-masked]" <[email-masked]>
Cc: "[email-masked]" <[email-masked]>, "[email-masked]" <[email-masked]>, "[email-masked]" <[email-masked]>
Date: Fri, 17 Feb 2017 08:59:15 +1300
List-Id: "IPv6 Maintenance Working Group \(6man\)" <ipv6.ietf.org>

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.