[153380] in North American Network Operators' Group
RE: IPv6 day and tunnels
daemon@ATHENA.MIT.EDU (Templin, Fred L)
Tue Jun 5 15:10:54 2012
From: "Templin, Fred L" <Fred.L.Templin@boeing.com>
To: Masataka Ohta <mohta@necom830.hpcl.titech.ac.jp>, "nanog@nanog.org"
<nanog@nanog.org>
Date: Tue, 5 Jun 2012 12:09:38 -0700
In-Reply-To: <4FCE51AD.5050601@necom830.hpcl.titech.ac.jp>
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 05, 2012 11:36 AM
> To: Templin, Fred L; nanog@nanog.org
> Subject: Re: IPv6 day and tunnels
>=20
> Templin, Fred L wrote:
>=20
> >> You don't have to do it with core routers.
> >
> > Tunnel endpoints can be located either nearer the edges
> > or nearer the middle. Tunnel endpoints that are located
> > nearer the edges might be able to do reassembly at nominal
> > data rates, but there is no assurance of a maximum MRU
> > greater than 1500 (which is too small to reassemble a
> > 1500+20 packet). Tunnel endpoints that are located nearer
> > the middle can be swamped trying to keep up with reassembly
> > at high data rates - again, with no MRU assurances.
>=20
> As operators know outer fragmentation is used to carry
> inner 1500B packets, the proper operation is to have
> equipments with large enough MRU.
>=20
> As core routers may be good at fragmentation but not
> particularly good at reassembly, operators do not
> have to insist on using core routers.
I am making a general statement that applies to all tunnels
everywhere. For those, specs say that all that is required
for MRU is 1500 and not 1500+20. *Unless there is some
explicit pre-arrangement between the tunnel endpoints*,
the ingress has no way of knowing whether the egress can
do better than 1500 outer packet (meaning 1480 inner packet).
That is certainly the case for point-to-multipoint "automatic"
tunnels as many of these IPv6 transition technologies are.
Fred
fred.l.templin@boeing.com
=20
> >> I'm afraid you don't understand tunnel operation at all.
> >
> > I don't? Are you sure?
>=20
> See above.
>=20
> Masataka Ohta
