IPv6 day and tunnels

Tue Jun 5 14:45:58 UTC 2012

> -----Original Message-----
> From: Masataka Ohta [mailto:mohta at necom830.hpcl.titech.ac.jp]
> Sent: Monday, June 04, 2012 4:40 PM
> To: Templin, Fred L; nanog at nanog.org
> Subject: Re: IPv6 day and tunnels
> 
> Templin, Fred L wrote:
> 
> > I'm not sure that a randomly-chosen "skip" value is even
> > necessary.
> 
> It is not necessary, because, for ID uniqueness fundamentalists,
> single event is bad enough and for most operators, slight
> possibility is acceptable.
> 
> > Outer fragmentation cooks the tunnel egresses at high
> > data rates.
> 
> Have egresses with proper performance. That's the proper
> operation.

How many core routers would be happy to reassemble at
line rates without a forklift upgrade and/or strong
administrative tuning?

> > End systems are expected and required to
> > reassemble on their own behalf.
> 
> That is not a proper operation of tunnels.

Why not?

> >> Thus, don't insist on having unique IDs so much.
> >
> > Non-overlapping fragments are disallowed for IPv6, but
> > I think are still allowed for IPv4. So, IPv4 still needs
> > the unique IDs by virtue of rate limiting.
> 
> Even though there is no well defined value of MSL?

MSL is well defined. For TCP, it is defined in RFC793.
For IPv4 reassembly, it is defined in RFC1122. For IPv6
reassembly, it is defined in RFC2460.

> >> I'm talking about not protocol recommendation but proper
> >> operation.
> >
> > I don't see any operational guidance recommending the
> > tunnel ingress to configure an MRU of 1520 or larger.
> 
> I'm talking about not operation guidance but proper
> operation.

The tunnel ingress cannot count on administrative tuning
on the egress - all it can count on is reassembly of 1500
or smaller and it can't count on good performance even
at those levels.

> Proper operators can, without any guidance, perform proper
> operation.

No amount of proper operation can fix a platform that
does not have adequate performance. And, there is no
way for the tunnel ingress to tell what, if any,
mitigations have been applied at the egress.

Thanks - Fred
fred.l.templin at boeing.com

> 					Masataka Ohta