pmtud problem

Alexander Motin mav at
Tue Feb 13 22:52:00 UTC 2007

Stephen Clark wrote:
>>> if the pc sends a packet of 1460 bytes with the DF bit set shouldn't the
>>> freebsd 4.9 system
>>> send back an icmp dest unreachable - fragmentation needed and DF bit 
>>> set?
>> Are you blocking icmp with a firewall filter?
> Good  question - but the answer is no. The other interesting fact is 
> when I drop the mtu on
> the gre to 1412 I do see the icmp messages.

Are you using any dummynet shapes? There is ancient bug in dummynet, 
which leads to not sending of ICMPs when shape used on outgoing interface.

Alexander Motin mav at
Optima Telecom

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