No they don’t? There are several 3p libs for it but not in std. Unless I’m blind and didn’t get the memo.

No you didn't miss. I mixed the concept, UDP broadcast similar to mDNS, yes part of net library. actual mDNS like visible in Finder and actual RFC implementation not part of standard library. What I was trying to say was easy to make "mdns-ish" with just standard lib, rush typed it and ended up like that.