IPv6 day and tunnels

Templin, Fred L Fred.L.Templin at boeing.com
Tue Jun 19 11:35:39 CDT 2012

> -----Original Message-----
> From: Masataka Ohta [mailto:mohta at necom830.hpcl.titech.ac.jp]
> Sent: Tuesday, June 19, 2012 6:10 AM
> To: Templin, Fred L
> Cc: Owen DeLong; nanog at nanog.org
> Subject: Re: IPv6 day and tunnels
> Templin, Fred L wrote:
> >> Not necessarily, as IPv4 can take care of itself and IPv6
> >> is hopeless.
> >
> > IPv4 can take care of it how - with broken PMTUD or
> 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?
> 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.
> > 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.
> Now, it's time for you to return v6-ops to defend your
> draft from Joe Touch.
> 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.l.templin at boeing.com
> 						Masataka Ohta

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