That's true. SQL knowledge is one of the few skills that didn't age.
1. C language.
2. *nix tools (shell and friends).
3. SQL.
4. Basic IPv4 networking.
These things I learned around 20 years ago, they didn't change much and they are useful for me to this day.
I was a fan of Seven Languages in Seven Weeks [1] because it exposed you to different paradigms which you could then try to apply where they made sense on whatever tools you were using or building: prototype based, fault tolerante, funcional, logical. Very fun book when used right.
The point being that sometimes the tools themselves don't need to survive because you take the lessons from one thing to another (e.g. move semantics and rust/modern c++)
[1] - https://pragprog.com/titles/btlang/seven-languages-in-seven-...
Well, IPv4 is obsolete.
Obsolete like your old iPhone is obsoleted by this year iPhone.
Doesn't mean it stops working or being useful, and in arguably IPv4 case it is still of far more importance than v6.
I inquired about getting a static IP(s) for a small business, and only v4 is available.... and that was this year!
All of the above are obsolete. But still what is regularly found out in the real world.
I'll believe that when I see tech companies bring up IPv6 integration before I do when setting up networking things.