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It's 2023 and I continue to see people write about IPv4 A,B,C,D, and E networking classes like they still mean something and without saying it's only mentioned for historical purposes. But they are now 30 years obsolete. Is there any point other than historical insight into teaching this stuff? The way books, tutorials and websites put it, they make it sound like address classes are some strict part of the protocol. But from what I understand, it was only a convention used to allocate addresses and determine what was in the routing table in the 80s and early 90s and just isn't really used anymore.

Examples of where this gets explained in recent texts on major websites and books:

And there are a ton more such examples.

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    Network address classes are dead (please let them rest in peace), killed in 1993 (two years before the commercial Internet in 1995), by RFCs 1517, 1518, and 1519, which defined CIDR (Classless Inter-Domain Routing). We have not used network address classes in this century. Unfortunately, in academia, textbooks and teaching are far slower than the pace of some technology, and courses and certifications keep old crap. Learn proper CIDR subnetting before polluting the knowledge with network address classes. See this two-part answer.
    – Ron Maupin ♦
    Jan 11 at 4:14
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    They were part of the protocol, until we changed it... 30 years ago. Today A, B, and C are almost universally slang for /8, /16, and /24 respectively. Many of those incorrectly using "class" don't even know there ever was classful networking. Personally, I think it's a valuable mistake people should learn not to repeat. (eg. IPv6 SLAAC's hard /64 mandate)
    – Ricky
    Jan 11 at 6:43

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