[153256] in North American Network Operators' Group
Re: IPv6 day and tunnels
daemon@ATHENA.MIT.EDU (Jeroen Massar)
Mon Jun 4 02:27:41 2012
In-Reply-To: <4FCC4A6F.30907@necom830.hpcl.titech.ac.jp>
From: Jeroen Massar <jeroen@unfix.org>
Date: Sun, 3 Jun 2012 23:27:04 -0700
To: Masataka Ohta <mohta@necom830.hpcl.titech.ac.jp>
Cc: "nanog@nanog.org" <nanog@nanog.org>
Errors-To: nanog-bounces+nanog.discuss=bloom-picayune.mit.edu@nanog.org
On 3 Jun 2012, at 22:41, Masataka Ohta <mohta@necom830.hpcl.titech.ac.jp> wr=
ote:
> Joe Maimon wrote:
>=20
>> So IPv6 fixes the fragmentation and MTU issues of IPv4 by how exactly?
>=20
> Completely wrongly.
Got a better solution? ;)
>> Or was the fix incorporating the breakage into the basic design?
>=20
> Yes.
>=20
> 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.
I do not see the problem that you are seeing, to adress the two issues in yo=
ur slides:
- for multicast just set your max packetsize to 1280, no need for pmtu and t=
hus this "implosion"
You think might happen. The sender controls the packetsize anyway and on=
e does not want
to frag packets for multicast thus 1280 solves all of it.
- when doing IPv6 inside IPv6 the outer path has to be 1280+tunneloverhead,=
if it is not then
you need to use a tunneling protocol that knows how to frag and reassemb=
le as is acting as a
medium with an mtu less than the minimum of 1280
Greets,
Jeroen
