Ethereal-users: Re: [Ethereal-users] PLEASE HELP WITH MY PROBLEM

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From: Guy Harris <gharris@xxxxxxxxx>
Date: Mon, 22 Aug 2005 23:57:29 -0700
john@xxxxxxxxxxxxxxx wrote:


I am running the software on a client machine 192.1681.100
i keep getting lots of checksum errors... i.e Checksum: 0x8450 [incorrect, should be 0xeac1] 


Please see below  sample packets below.

this must mean something is corrupting the data (what ???)
Not necessarily. If the packets are being sent by the machine that's running Ethereal, and they're being sent on a network adapter that supports TCP checksum offloading, and the operating system and driver for the network adapter support checksum offloading, then TCP packets sent on that adapter will, when seen by Ethereal - or any *other* network analyzer program - not have a valid checksum, because the checksum isn't computed for the packet, and set on the packet, until the packet has been supplied to the network adapter, and the adapter doesn't give to the host a copy of the packet with the checksum added. 

That's probably what's happening here.

This is in the Ethereal FAQ:

	http://www.ethereal.com/faq#q5.14