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I liked this one * Do not calculate IP, TCP, and UDP checksums on lo(4) interfaces.
by anotherhue 3y ago
I liked this one
* Do not calculate IP, TCP, and UDP checksums on lo(4) interfaces.
- dark-star 3y agoso, a tcpdump/wireshark trace on lo will now show all packets as red/bad? That sounds annoying. But I get why they did it, it probably makes sense in most real-life scenarios
- petee 3y agoThis is the commit for those curious: https://github.com/openbsd/src/commit/c778c0d73570b51def4f061069af442165eb791e https://github.com/openbsd/src/commit/c778c0d73570b51def4f06... > Packets sent over loopback got their checksums calculated twice. In the output path they were filled in and during TCP/IP input all checksums were calculated again to be compared with the previous result. Avoid this by claiming that lo(4) supports hardware checksum offloading. For each packet convert the flag that the checksum should be calculated to the flag that it has been checked successfully. Keep the flag that it should be calculated for the case that it may be bridged or forwarded later. A drawback is that "tcpdump -ni lo0 -v" reports invalid checksum. But that is the same with physical interfaces and hardware offloading. OK dlg@