Technology and science fiction author Michael W. Lucas has observed the adoption Classless Interdomain Routing (CIDR) networking as a technology milestone [mwl.io] from 1993. Back on 24 September 1993, the IETF published RFC 1519 thus designating Classless Interdomain Routing (CIDR) and variable length subnet masks as the standard and it described in a series of RFCs. So Monday was the 25th anniversary of the occasion.