Re: transmech MTU comments

[Erik Nordmark <Erik.Nordmark@Sun.COM>]

> My understanding of RFC 3168 is that when the tunnel interface
> forwards an IPv6 packet to an IPv4 interface with an ECT(0) or ECT(1)
> codepoint in the traffic class field, it MAY set the codepoint to CE if
> congestion is experienced. I interpret the MAY to mean that the other
> option is to drop the packet. If the packet is to be dropped, should it
> be dropped silently? Also, could a link restriction be considered as
> congestion? If so, does drop silent also entail NOT sending an
> ICMPv6 "packet too big" message back to the source?

My understanding is that larger than MTU is not congestion, that
packets would not be dropped as an alternative to setting CE, and
that congestion for tunnels isn't any different than congestion in general.

What tunnel adds is the question of what the encasulator puts in the ECT
bits in the outer header (where copying them from the inner header
makes sense in many cases) and whether the decapulator does anything with
the received ECT bits in the outer header (and I think that 3168 says
that unless there are security concerns, copying them from the outer
to the inner header makes sense).

Thus I think the text in the mech document about ECN are sufficient.

  Erik