Hi Ole,
-----Original Message-----
From: otroan(_at_)employees(_dot_)org [mailto:otroan(_at_)employees(_dot_)org]
Sent: Tuesday, February 14, 2017 11:17 AM
To: Templin, Fred L <Fred(_dot_)L(_dot_)Templin(_at_)boeing(_dot_)com>
Cc: Stewart Bryant <stewart(_dot_)bryant(_at_)gmail(_dot_)com>; Brian E
Carpenter <brian(_dot_)e(_dot_)carpenter(_at_)gmail(_dot_)com>;
gen-art(_at_)ietf(_dot_)org; 6man WG
<ipv6(_at_)ietf(_dot_)org>; ietf(_at_)ietf(_dot_)org;
draft-ietf-6man-rfc1981bis(_dot_)all(_at_)ietf(_dot_)org
Subject: Re: [Gen-art] Review of draft-ietf-6man-rfc1981bis-04
Fred,
Yes, but sending at 1280 does not work for IP tunnels. The whole purpose
of the minimum MTU was to give space for tunnel
headers
(1500-1280).
But, if non-tunnel links set a 1280 MTU which is perfectly OK with the
standard then
there is no space for headers. Given the issues with classical PMTUD then
(plus the
non-applicability of RFC4821 for tunnels) the only solution for tunnels is
fragmentation.
I'll let Joe step in if he wants to.
You are correct. "Does not work for IP tunnels without fragmenting the outer
header" is what I should have written.
Of course it appears IPv6 fragments have a order of magnitude higher drop
probability than ICMP PMTUD messages.
Right. Depending on the encapsulation, however, fragmentation might occur as
some mid-layer between the outer and inner IP headers. For example, a UDP
encapsulation that includes its own fragmentation control fields. In that way,
the network would only see UDP/IP packets - it would not see IPv6 fragments.
GUE is an example UDP encapsulation that include its own fragmentation
control fields:
https://datatracker.ietf.org/doc/draft-herbert-gue-extensions/
Pick your poison.
As far as RFC 2473 is concerned, you are right. Other encapsulations that
can do the fragmentation at a mid-layer between the inner and outer
IP headers should be OK.
Thanks - Fred
Best regards,
Ole