MTU handling in 6RD deployments

Templin, Fred L Fred.L.Templin at
Fri Jan 17 17:20:28 CET 2014

Hi Mikael,

> -----Original Message-----
> From: Mikael Abrahamsson [mailto:swmike at]
> Sent: Friday, January 17, 2014 8:15 AM
> To: Templin, Fred L
> Cc: Mark Townsley; ipv6-ops at
> Subject: RE: MTU handling in 6RD deployments
> On Fri, 17 Jan 2014, Templin, Fred L wrote:
> > Sorry, I was looking at the wrong section. I see now that Section 8 is
> > talking about a method for a CE to send an ordinary data packet that
> > loops back via the BR. That method is fine, but it is no more immune to
> > someone abusing the mechanism than would be sending a ping (or some
> > other NUD message). By using a ping, the BR can impose rate-limiting on
> > its ping responses whereas with a looped-back data packet the BR really
> > can't do rate limiting.
> You don't ping the BR, you ping yourself via the BR. The BR only forwards
> the packet.
> > Also, Section 8 of RFC5969 only talks about the CE testing the forward
> > path to the BR. Unless the BR also tests the reverse path to the CE it
> > has no way of knowing whether the CE can accept large packets.
> You misread the text.

I don't see anywhere where it says that the BR should also ping the
CE and cache a boolean "ACCEPTS_BIG_PACKETS" for this CE. If the BR
doesn't do that, it needs to set its MTU to the CE to 1480 (or 1472
or something).

Thanks - Fred
fred.l.templin at

> --
> Mikael Abrahamsson    email: swmike at

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