On Tue, 18 Dec 2018 17:12:45 -0500, "David Edelman" said:
I seem to remember that before the advent of VLSM and CIDR there was no requirement for the 1 bits in the netmask to be contiguous with no intervening 0 bits and there was always someone who tested it out on a production network just to prove a point (usually only once)
So at one show, the Interop show network went to a 255.255.252.0 netmask, and of course a lot of vendors had issues and complained. The stock response was "Quit whining, or next show it's going to be 255.255.250.0". There was indeed a fairly long stretch of time (until the CIDR RFC came out and specifically said it wasn't at all canon) where we didn't have an RFC that specifically said that netmask bits had to be contiguous.