IPv6 day and tunnels

Tue Jun 5 22:01:55 UTC 2012

> -----Original Message-----
> From: Masataka Ohta [mailto:mohta at necom830.hpcl.titech.ac.jp]
> Sent: Tuesday, June 05, 2012 2:44 PM
> To: Templin, Fred L; nanog at nanog.org
> Subject: Re: IPv6 day and tunnels
> 
> 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.

I should qualify that by saying:

  1) For tunnels over IPv4, let infinity equal (2^16 - 1)
     minus the length of the encapsulation headers

  2) For tunnels over IPv6, let infinity equal (2^32 - 1)
     minus the length of the encapsulation headers

> > 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.

Are you interested in only supporting tinygrams? IMHO,
go big or go home!

Fred
fred.l.templin at boeing.com

> 					Masataka Ohta