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Bad Checksum errors

Posted on 2011-02-14
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Last Modified: 2012-06-27
Hi Guys,

What could be the issue of Bad checksum IP packets? I have collected some captures from Nortel switch stack and I am seeing lots of Bad Checksum and packets and retransmissions from one of the switches(speed less than 10KB) other switches looks fine ( Speed 20 MB). I know it's a fault switch but i wold like to know why it's causing Bad Checksum tcp packets.

Thanks in advance!
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Question by:smartnet
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Expert Comment

by:jjmartineziii
ID: 34889639
more than likely, you have Checksum offloading to your nic. the nic calculates the checksum right before the wire and when you capture from the OS, you see 00000 as the checksum as it hasn't been calculated yet. turn off checksum offloading from your nic driver if you want to see the checksums.
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by:jjmartineziii
ID: 34889647
oops, i read wrong. how are you capturing? a span session?
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Author Comment

by:smartnet
ID: 34889715
not span, directly form the PC that is having issue.
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jjmartineziii earned 500 total points
ID: 34889728
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