[skeletonjelly]

I think they've got Class A/B/C wrong? Or at least they're using it in a way that I never learnt

> The familiar 192.168.140.255 notation is technically the “Class C” notation. You can also write that address in “class B” notation as 192.168.36095, or in “Class A” notation as 192.11046143. What we’re doing is coalescing the final bytes of the address into either a 16-bit or a 24-bit integer field.

According to this:

https://www.digitalocean.com/community/tutorials/understandi...

Which details my understanding, classes refer to the ranges, not so much grouping the latter part

Happy to be corrected!

[voxic11]

from the linked article

> Traditionally, each of the regular classes (A-C) divided the networking and host portions of the address differently to accommodate different sized networks. Class A addresses used the remainder of the first octet to represent the network and the rest of the address to define hosts. This was good for defining a few networks with a lot of hosts each.

[skeletonjelly]

There you go, thanks! Should have properly read the article I linked. So it's been repurposed to be as OP's linked article states? Not so much ranges but the amount of bits in the netmask?

[dfox]

It is other way around: in the original class-ful internet the numerical range of first octet directly implied what is in CIDR called netmask length. The original IPv4 implementations probably did not even have concept of netmask and this was instead hardcoded. Implementing the routing decision as netmask is nice optimalization which then probably inspired the CIDR concept, because at sufficently high level the only thing you need for that to work is making the netmask (or at least the length) freely configurable.