[153254] in North American Network Operators' Group
Re: IPv6 day and tunnels
daemon@ATHENA.MIT.EDU (Masataka Ohta)
Mon Jun 4 01:42:30 2012
Date: Mon, 04 Jun 2012 14:41:03 +0900
From: Masataka Ohta <mohta@necom830.hpcl.titech.ac.jp>
To: nanog@nanog.org
In-Reply-To: <4FCC11B2.2090405@ttec.com>
Errors-To: nanog-bounces+nanog.discuss=bloom-picayune.mit.edu@nanog.org
Joe Maimon wrote:
> So IPv6 fixes the fragmentation and MTU issues of IPv4 by how exactly?
Completely wrongly.
> Or was the fix incorporating the breakage into the basic design?
Yes.
Because IPv6 requires ICMP packet too big generated against
multicast, it is designed to cause ICMP implosions, which
means ISPs must filter ICMP packet too big at least against
multicast packets and, as distinguishing them from unicast
ones is not very easy, often against unicast ones.
For further details, see my presentation at APNIC32:
http://meetings.apnic.net/32/program/apops
How Path MTU Discovery Doesn't work
Masataka Ohta
> In IPv4 I can make tunneling just work nearly all of the time. So I have
> to munge a tcp mss header, or clear a df-bit, or fragment the
> encapsulated packet when all else fails, but at least the tools are
> there. And on the host, /proc/sys/net
FYI, IETF is trying to inhibit clearing DF bit explicitly with
draft-ietf-intarea-ipv4-id-update-05.txt
>> IPv4 datagram transit devices MUST NOT clear the DF bit.
which is now under the last call.
Masataka Ohta
