RE: IPv6 day and tunnels

["Templin, Fred L" <Fred.L.Templin () boeing com>]

> -----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
>
> Templin, Fred L wrote:
>
> > > 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.
>
> As operators know outer fragmentation is used to carry
> inner 1500B packets, the proper operation is to have
> equipments with large enough MRU.
>
> 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
 
> > > I'm afraid you don't understand tunnel operation at all.
> >
> > I don't? Are you sure?
>
> See above.
>
>                                       Masataka Ohta