nanog mailing list archives

Re: IPv6 day and tunnels


From: Masataka Ohta <mohta () necom830 hpcl titech ac jp>
Date: Wed, 06 Jun 2012 06:44:22 +0900

Templin, Fred L wrote:

General statement for IPv6-in-IPv4 tunneling, yes. But
inner fragmentation applies equally for *-in-* tunneling.

Even though you assume tunnel MTU 1500B

What I am after is a tunnel MTU of infinity. 1500 is
the minimum packet size that MUST get through. 1501+
packets are admitted into the tunnel unconditionally
in hopes that they MIGHT get through.

Infinity? You can't carry 65516B in an IPv4 packet.

My document also allows for outer fragmentation on the
inner fragments. But, like the RFC4213-derived IPv6
transition mechanisms treats outer fragmentation as
an anomalous condition to be avoided if possible - not
a steady state operational approach. See Section 3.2
of RFC4213.

Instead, see the last two lines in second last slide of:

   http://meetings.apnic.net/__data/assets/file/0018/38214/pathMTU.pdf

It is a common condition.

                                        Masataka Ohta


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