Test your connectivity for World IPv6 Day

Tore Anderson tore.anderson at redpill-linpro.com
Tue Jun 7 15:56:49 CEST 2011

* Rémi Després

> Le 7 juin 2011 à 00:20, Tore Anderson a écrit :
>> It's quite hard to discover the blackholes (and by extension fix
>> them) if you're defaulting to 1280.
> Which blackholes? - With 1280, there isn't any related to MTU's.
> Right?

Wrong. The blackholes are still there. Masking the symptoms does not fix
the underlying problem.

>> In any case, the few users that have HE/SixXS/etc. tunnels can take
>> care of themselves. If it breaks, they get to keep both parts.
> Too bad for IPv6!
>> For real deployments, on the other hand ... well, I'm hoping no
>> serious ISP or content provider will willingly put their end users
>> or web sites behind MTU-impaired links or tunnels. Recipe for
>> disaster if you ask me.
> What do you mean, precisely, by "MTU-impaired links or tunnels"?

If an ISP, a tunnel broker, or a concious tunnel-using end user are
using a link/tunnel that has a MTU lower than 1500 but where PMTUD does
not work reliably, that is their problem, not mine. I refuse to work
around their defective network by crippling the MTU for all my visitors.

What MTU do you recommend for IPv4 servers, by the way? 576 or 68?

Tore Anderson
Redpill Linpro AS - http://www.redpill-linpro.com/
Tel: +47 21 54 41 27

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