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TCP checksum offload

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Cristiano

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Dec 30, 2009, 7:25:51 PM12/30/09
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I see that many packets captured with Wireshark have a wrong checksum:
Checksum: 0x38ae [incorrect, should be 0xb197 (maybe caused by "TCP checksum
offload"?)].
Is that a problem?

Thanks
Cristiano


John Wunderlich

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Dec 30, 2009, 9:15:23 PM12/30/09
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"Cristiano" <cristi...@NSquipo.it> wrote in
news:4b3bef70$1...@news.x-privat.org:

Not usually a problem. Wireshark views packets as they are sent
to/from the NIC. Most NICs have an option that the NIC itself will
insert the checksum as the packet goes out instead of making the TCP
stack pre-calculate it and insert it (i.e. the job of inserting
checksum has been "offloaded" to the NIC). See the Advanced settings
in the device manager for your NIC for the offload option. If you
view the same packet with Wireshark from the destination computer on
the network, you will probably see a correct checksum.

HTH,
John

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