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Re: MTU and Postfix

On Sun, 04 Sep 2011 14:06:02 +0200, Markus Schönhaber wrote:

> 04.09.2011 12:40, Camaleón:
>>> I'm still monitoring this but if this is the "cure" to prevent such
>>> errors, are there any expected drawbacks for lowering MTU
>>> "system-wide"?
>> (...)
>> Mmm, no replies yet...
>> Does it mean then that there are no gotchas to care about in setting a
>> MTU value of 1400 for a bonded interface? :-)
> I don't see any gotchas besides the obvious one: the throughput is
> decreased somewhat, since on average more packets are needed to transmit
> the same amount of payload.
> OTOH, in my experience, when you can work around transmission problems
> by lowering the MTU, almost always someone has b0rked his packet filter
> and throws away those ultra-evil ICMP packets like "Fragmentation
> Needed" or "Time Exceeded in Transit" etc. If you're sure you're not the
> one killing ICMP and the problems only occur with specific sites, it
> might be helpful to have the administrators of those sites check their
> "firewall" configuration.

I agree. The best way to sort out these problems is by carrying out 
additional tests with the host we were experiencing problems but I've had 
not very good experiences when contacting Spanish admins, most of them 
just don't reply at all or are not interested in solving this 
problematic ;-(



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