Re: Too bigs are sacred, was: Re: IPv6 addressing for core network

[Owen DeLong <owen () delong com>]

On Feb 9, 2011, at 9:50 AM, David Freedman wrote:

> Iljitsch van Beijnum wrote:
> > On 9 feb 2011, at 18:30, David Freedman wrote:
> >
> > > (yes, even ICMP TOOBIG
> > > can be filtered safely if you have designed things in a sane way)
> >
> > NO.
> >
> > Even if you run with 1280-byte MTUs everywhere so you'd think path MTU discovery wouldn't be needed, this can still 
> > cause problems with IPv6-to-IPv4 translators.
>
> Calm down, I think you misunderstand,
>
> I'm suggesting that you don't design your infrastructure in such a way
> that your backbone/infrastructure links ever have to receive TOOBIG
> messages from outside your AS and work with these, your backbone links
> are of course free to send TOOBIG out!
>
> Dave.
>
> -- 
>
>
> David Freedman
> Group Network Engineering
> Claranet Group

Unless every packet you emit is ≤ the minimum MTU (1280), then, you need
to be able to receive TOOBIG messages.

Owen