-----Original Message----- From: Masataka Ohta [mailto:mohta@necom830.hpcl.titech.ac.jp] Sent: Tuesday, June 05, 2012 2:44 PM To: Templin, Fred L; nanog@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@boeing.com
Masataka Ohta