Ethereal-users: [Ethereal-users] Why am I seeing lots of packets with incorrect UDP checksums?

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From: "Hoehle, Joerg-Cyril" <Joerg-Cyril.Hoehle@xxxxxxxxxxxxx>
Date: Fri, 14 Jul 2006 17:02:26 +0200
Hi,

When upgrading from Debian Ubuntu Breezy to Dapper, I was hit by the "all outgoing TCP & UDP(!) checksums incorrect" symptom.
I came across the FAQ http://www.ethereal.com/faq.html#q11.1

As of Ethereal 0.99.0 as distributed in Ubuntu, the preferences dialog allows to disable the checksum check for TCP and IP protocols:
+/- Validate the IP|TCP checksum if possible

But UDP has no such switch. As a result, all outgoing DNS requests are marked red & incorrect on my machine.

Note that the IP checksum is reported correct with my laptop:
lspci: Realtek Semiconductor Co., Ltd. RTL-8139/8139C/8139C+ (rev 10)
I'd have expected a hardware able to fix the TCP checksum to also manage the IP one. How comes?

[Enhancement request #2 follows:]
Sadly, this preferences setting deactivates checksums even for
incoming packets, which is not good.  A single switch "*outgoing*
checksums done in HW, please don't check" would be preferable,
possibly per interface.

Regards,
	Jörg Höhle
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