Originally Posted by
mixture
Agree with you about defensive programming, however "design by committee" appear to have eventually agreed on the word "should" instead of "must" !
It was never in the original RFC. Purely an addition by Microsoft in SP1 of Server 2003, and given how many years DHCP predates 2003 gives you an idea of the amount of implementations that were out there without it. Even now it's not anywhere near the majority, especially in open source packages chosen for size to stuff into router firmware.
I once lobbied a pair of blokes from IBM who had proposed an addition to the RFC for DHCP to specify the DNS suffix search list. Nothing ever came of it either.