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Date:      Fri, 7 Mar 2008 09:18:51 +0500
From:      "Sergey" <_lion_2000@mail.ru>
To:        <freebsd-net@freebsd.org>
Subject:   RE: Path MTU Problem
Message-ID:  <001101c8800a$596d4220$37c9010a@Net.ARDS.Corp>
In-Reply-To: <20080306161818.GD15130@verio.net>
References:  <000001c87f43$c8075800$37c9010a@Net.ARDS.Corp> <20080306161818.GD15130@verio.net>

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> Is it possible that you have PF or IPFW filter rules in place 
> that drop ICMP?  Just because tcpdump shows you the frame 
> arrived at your system, does not mean that it was "seen" by 
> the kernel.

No, it's virgin clean install, without any packet filtering enabled

> > here comes icmp frag packets. strange what sometimes 
> tcpdump complains 
> > about tcp header in icmp packet and sometimes not
> 
> The reason for this complaint is that frag_needed packets 
> return a portion of the original IP frame back to the sender, 
> but the number of bytes is not sufficient to see the entire 
> TCP header.  However, there is enough to see the src/dest 
> IP's and src/dest port numbers, as tcpdump shows you.  But 
> tcpdump cannot decode past the end of the returned frame, so 
> it shows an error.

I c




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