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 From:  "Chris Buechler" <cbuechler at gmail dot com>
 Cc:  m0n0wall at lists dot m0n0 dot ch
 Subject:  Re: [m0n0wall] MTU problems - missing source quench
 Date:  Sat, 29 Sep 2007 10:25:13 -0400
> Hi experts,
>
> I'm running monowall version 1.231 (and several other versions). I often see
> MTU problems - especially when using Captive portal and a bridged wireless
> network on the OPT1 interface.
>
> Most of the time the connectivity problems can be solved by setting the MTU
> to 1300 for all interfaces. I have not found the underlying reasons for the
> problems - but i believe it has something to do with missing ICMP source
> quench packages.
>

No, it's caused by something somewhere not sending ICMP frag needed
but DF bit set messages. "A router SHOULD NOT originate ICMP Source
Quench messages." - RFC 1812.  I don't think any OS sends ICMP source
quench messages by default, TCP has its own congestion avoidance
mechanisms. Regardless, congestion won't cause MTU-related problems,
so that's not related.

-Chris