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From: Charles Swiger <cswiger@mac.com>
Date: Mon, 28 Nov 2005 14:55:30 -0500
To: John Palmer <drgnut@hotmail.com>
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Cc: FreeBSD Q ML <freebsd-questions@freebsd.org>
Subject: Re: bad udp cksum 26ff!
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On Nov 28, 2005, at 1:46 PM, John Palmer wrote:
> I am running FreeBSD 5.4 p8.  I did a tcpdump -vv -i em0.  The  
> output produced
> a "bad udp cksum" with my DNS server.  Does anyone know what it  
> means?  Or, how I can
> correct the problem?

If you are sniffing traffic from the machine  itself, tcpdump is  
seeing the packets before the networking stack has computed the  
packet checksums...this is especially likely to be true if the TXCSUM  
option is on, check ifconfig.

In order to double-check this, try sniffing the traffic from another  
machine.

-- 
-Chuck