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?
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.