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Vishal
Asked: 2011-07-09 14:21:36 +0800 CST

Too many incorrect checksum errors in TCPDUMP

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I find too many incorrect checksum errors from a TCPDUMP done on a GNU Linux 64bit server. There are close to 50% incorrect chekcsums in the export?

cksum 0xe61f (incorrect (-> 0x8c37)

How can we interpret this data? Does it affect performance a lot?

network-monitoring tcpdump checksum

1 Answers

  1. Best Answer

    You see the "incorrect" checksums due to a feature called TCP checksum offloading. The checksum fields for outgoing TCP packets are not pre-calculated by the operating system but instead set to 0 and left for calculation by the NIC processor. The Wireshark FAQ has a more detailed explanation.

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