I'm so old that I predate CIDR and in the old days before netmasks the netmask was essentially implied by the first couple bits of an ip address so all msb zero

I'm so old that I predate CIDR and in the old days before netmasks the netmask was essentially implied by the first couple bits of an ip address so all msb zero ip addrs were class A aka /8 allocations. All MSB 00 or whatever it was were class B implying a netmask of 255.255.0.0 aka a /16 allocation. Before CIDR you couldn't route or advertise rando netmasks like a /9 or a /20. There were no steps between a /16 and a /8 so if you convinced (someone, forget who) that you "need" more than 65K ip addresses (and MIT is big enough to need more, theoretically) then you got a /8. A lot of noobs think ipv4 rolled out with CIDR; not so. For "a long time" people had to make due with classful routing. From memory, isn't RIP v1 only classful routing compatible? Been awhile since I used something that old.