protocol checksums: PCBs and templating


BSD-derived stacks use "Protocol Control Blocks"
to track connections / keep state
connection-less UDP still has some state, kept in PCBs
PCBs looked up using hashtables
in OpenBSD: pf states linked to PCBs, saving lookups

when a socket is opened, a template PCB is created
think bound listening socket, easiest case
known IP header parts are filled in
and checksummed!