[153955] in North American Network Operators' Group
RE: IPv6 day and tunnels
daemon@ATHENA.MIT.EDU (Templin, Fred L)
Tue Jun 19 12:36:57 2012
From: "Templin, Fred L" <Fred.L.Templin@boeing.com>
To: Masataka Ohta <mohta@necom830.hpcl.titech.ac.jp>
Date: Tue, 19 Jun 2012 09:35:39 -0700
In-Reply-To: <4FE07A3B.8080900@necom830.hpcl.titech.ac.jp>
Cc: "nanog@nanog.org" <nanog@nanog.org>
Errors-To: nanog-bounces+nanog.discuss=bloom-picayune.mit.edu@nanog.org
> -----Original Message-----
> From: Masataka Ohta [mailto:mohta@necom830.hpcl.titech.ac.jp]
> Sent: Tuesday, June 19, 2012 6:10 AM
> To: Templin, Fred L
> Cc: Owen DeLong; nanog@nanog.org
> Subject: Re: IPv6 day and tunnels
>=20
> Templin, Fred L wrote:
>=20
> >> Not necessarily, as IPv4 can take care of itself and IPv6
> >> is hopeless.
> >
> > IPv4 can take care of it how - with broken PMTUD or
>=20
> As you know, RFC1191 style PMTUD is broken both for IPv4
> and IPv6.
Unfortunately, there is evidence that this is the case.
> > with broken fragmentation/reassembly?
>=20
> Fragmentation is fine, especially with RFC4821 style PMTUD,
> even though RFC4821 tries to make people believe it is broken,
> because accidental ID match is negligibly rare even with IPv4.
The 16-bit IP ID, plus the 120sec MSL, limits the rate
for fragmentable packets to 6.4Mbps for a 1500 MTU.
Exceeding this rate leads to the possibility of
fragment misassociations (RFC4963). This would not
be a problem if there were some stronger integrity
check than just the Internet checksum, but with the
current system we don't have that.
=20
> > And, you won't
> > get any argument from me that IPv6 has been stuck
> > for years for good reasons - but MTU failures can
> > soon be taken off the list.
>=20
> Now, it's time for you to return v6-ops to defend your
> draft from Joe Touch.
>=20
> Note that there is no point for IPv6 forbid fragmentation
> by intermediate routers.
I wasn't there when the decision was made, but based
on my findings I don't disagree.
Fred
fred.l.templin@boeing.com
=20
> Masataka Ohta
