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Date: Mon, 28 Nov 2005 21:49:31 -0500
From: Kris Kennaway <kris@obsecurity.org>
To: John Palmer <drgnut@hotmail.com>
Message-ID: <20051129024931.GA34483@xor.obsecurity.org>
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Cc: freebsd-net@freebsd.org, freebsd-questions@freebsd.org
Subject: Re: bad udp cksum 26ff!
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On Mon, Nov 28, 2005 at 10:46:38AM -0800, John Palmer wrote:
> I am running FreeBSD 5.4 p8.  I did a tcpdump -vv -i em0.  The output=20
> produced
> a "bad udp cksum" with my DNS server.  Does anyone know what it means?  O=
r,=20
> how I can
> correct the problem?

If your NIC is doing checksum offload, tcpdump on the host won't see
the right checksum, since it's only generated on the way out the door.
Run tcpdump on another host on the network to verify whether it's
correct on the wire.

Kris

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