On 9/29/07, Søren Vanggaard Jensen <svanggaard at hotmail dot com> wrote:
> 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.