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

Owen DeLong owen at delong.com
Wed Feb 9 16:11:32 CST 2011


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





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