[Nil]

127 range is reserved for loopback and not typically included in the class listing

http://www.vlsm-calc.net/ipclasses.php


While CIDR is basically law of the land these days, you have to understand this foundation to understand subnetting and understand how routers see IP addresses. That was the main point I didn't get to yet and likely will when I'm less tired.

That's why I said technically. If you go off how the classes are organized by the prefixes, then 127 would fall into class A, although you're right, loopback and shit. And I don't see any reason on how understanding classful before CIDR would help in understanding the current architecture of the of the network. Maybe purely from a historical standpoint it is worth being aware of.

Classful networking still exists, it's the default subnet mask. CIDR requires an understanding of the bits so you can understand how a to subnet a network range.

https://learningnetwork.cisco.com/thread/34420

Class A would be a /8 if you didn't modify the subnet mask, Class B is a /16, and Class C is a /24. the /X number represents the number of bits in the "on" position of the subnet mask.

So default subnet mask for a class A address is 255.0.0.0, which is 11111111.00000000.00000000.00000000. You have 8 bits w/ a 1. A /16 would be 11111111.11111111.00000000.00000000, or 255.255.0.0.
If you had a Class B address with a subnet mask of 255.255.128.0, that would look like 11111111.11111111.10000000.00000000. This would also be represented in CIDR notation as a /17, because there are 17 bits in the "on" position.

One isn't required to understand the other. In fact, it would probably be better if off to do away with classifying anything with a class. Firstly, most people in the industry will laugh. Secondly, working backwards from a CIDR address won't always correlate with the correct class (A, B, C) based on the mask and just serves to confuse people. You're saying it still exists, but that's just an unneeded correlation between an explicitly stated subnet mask to a particular class, and in no way gives any kind of importance to the classes in the current architecture.