IPv6 day and tunnels

Tue Jun 5 17:46:08 UTC 2012

> -----Original Message-----
> From: Masataka Ohta [mailto:mohta at necom830.hpcl.titech.ac.jp]
> Sent: Tuesday, June 05, 2012 9:37 AM
> To: Templin, Fred L
> Cc: nanog at nanog.org
> Subject: Re: IPv6 day and tunnels
> 
> Templin, Fred L wrote:
> 
> >> 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?
> 
> 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.

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

Huh?

> >> 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.
> 
> As you can see, they are different values.

RFC793 sets MSL to 120 seconds. RFC1122 uses MSL as the upper
bound for reassembly buffer timeouts. IPv6 doesn't reference
MSL but sets reassembly buffer timeouts to 60 seconds.

Personally, I can't imagine a reassembly that takes even as
long as 30seconds being of any use to the final destination
even if it were to finally complete. But, if we set 60 sec
as the reassembly timeout value for IPv* I'm sure we'd be OK.

> >> I'm talking about not operation guidance but proper
> >> operation.
> >
> > The tunnel ingress cannot count on administrative tuning
> > on the egress
> 
> I'm afraid you don't understand tunnel operation at all.

I don't? Are you sure?

> > No amount of proper operation can fix a platform that
> > does not have adequate performance.
> 
> Choosing a proper platform is a part of proper operation.

This is getting tiresome.

Fred
fred.l.temlin at boeing.com

> 					Masataka Ohta