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Date: Wed, 14 Feb 2007 00:51:57 +0200
From: Alexander Motin <mav@alkar.net>
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To: Stephen.Clark@seclark.us
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Cc: freebsd-net@freebsd.org
Subject: Re: pmtud problem
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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@alkar.net
Optima Telecom