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Published on May 18, 2012
Dealing with the IP checksum and the protocol checksums (foremost TCP and UDP) in the network stack is surprisingly complex. Having stumbled over an unexpected performance penalty from the IP checksum, I always had this area on my mental todo - and when we stumbled over a really nasty piece of code in pf dealing with these checksums, I re-evaluated and changed the IP checksumming in our stack, for performance and to make better use of checksum offloading to network cards. Changing the protocol checksums in the same way is harder and in the works.
ALTQ has been with us for more than a decade - last not least Kenjiro Cho and myself merged it with pf in 2003. ALTQ has always been a research project, and tought us and the entire community a lot of important lessons. Now it is time to re-evaluate - the entire "glue" between the actual queueing disciplines (of which just two remain, prio and bandwidth shaping) gets redesigned and -implemented.