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Date:      Tue, 13 Feb 2007 13:18:59 -0500
From:      Stephen Clark <Stephen.Clark@seclark.us>
To:        dart@es.net
Cc:        freebsd-net@freebsd.org
Subject:   Re: pmtud problem
Message-ID:  <45D20113.1060403@seclark.us>
In-Reply-To: <45D1F216.1090708@es.net>
References:  <45D1E669.30402@seclark.us> <45D1F216.1090708@es.net>

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Eli Dart wrote:

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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?
>
>		--eli
>
>  
>
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.

>>$ sysctl -a | grep mtu
>>net.inet.tcp.path_mtu_discovery: 1
>>
>>Now if I change the mtu of the gre to 1412 everything works.
>>
>>Any insight would be appreciated.
>>
>>Thanks,
>>Steve
>>    
>>
>
>- --
>Eli Dart                                         Office: (510) 486-5629
>ESnet Network Engineering Group                  Fax:    (510) 486-6712
>Lawrence Berkeley National Laboratory
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