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

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From: Guy Harris <guy@xxxxxxxxxxxx>
Date: Thu, 27 Jul 2006 12:42:08 -0700
Hoehle, Joerg-Cyril wrote:

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?

I don't know. You might want to ask whoever maintains the driver for those adapters.

[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.

A mechanism for determining whether a packet is incoming or outgoing would be a requirement for this. Unfortunately, there isn't yet such a mechanism in libpcap/WinPcap, so, for captures done with libpcap/WinPcap-based applications (such as Wireshark), that's not doable.
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