Re: 6MAN: Adoption call on draft-hinden-6man-rfc1981bis-01

[Tore Anderson <[e-mail]>]

* [e-mail]

> This message starts a two week 6MAN call on adopting:
> 
> Name:	draft-hinden-6man-rfc1981bis-01
> Title:	Path MTU Discovery for IP version 6
> Document date:	2015-12-01
> Pages:	16
> URL:         https://datatracker.ietf.org/doc/draft-hinden-6man-rfc1981bis/
> Htmlized:  https://tools.ietf.org/html/draft-hinden-6man-rfc1981bis-01
> Diff:          https://tools.ietf.org/rfcdiff?url2=draft-hinden-6man-rfc1981bis-01.txt
> 
> as a working group item. Substantive comments and statements of support
> for adopting this document should be directed to the mailing
> list. Editorial suggestions can be sent to the authors.

I support adoption.

I see one issue that I would like to remind the WG about:

   A node MUST NOT reduce its estimate of the Path MTU below the IPv6
   minimum link MTU.

-     Note: A node may receive a Packet Too Big message reporting a
-     next-hop MTU that is less than the IPv6 minimum link MTU.  In that
-     case, the node is not required to reduce the size of subsequent
-     packets sent on the path to less than the IPv6 minimun link MTU,
-     but rather must include a Fragment header in those packets
-     [I-D.ietf-6man-rfc2460bis].

The lines prefixed with "-" have been removed in -01. In my opinion,
this leaves the text in an ambiguous state. What is a node conforming
to -01 expected to do, when receiving a PTB reporting a next-hop MTU
lower than 1280? I see two distinct options:

a) Reduce its PMTU estimate to exactly 1280.
b) Ignore the "invalid" PTB (retaining its previous PMTU estimate).

I think it would be preferable to replace the removed paragraph with a
clarification as to which behaviour is the correct and expected one. I
do not know which one that would be, though.

Tore