Hardcoded and unique network addresses for every single device on Earth.
Started with 48 bits (6 bytes), usually given as 01:23:45:67:89:AB but people now encouraged to use 64-bit ones.
How they are assigned: www.quora.com/How-are-MAC-addresses-assigned Basically IEEE gives out the 3 first bytes to device manufacturers that register, this is called the organizationally unique identifier, and then each manufacturer keeps their own devices unique.
Video 1. The Internet Protocol by Ben Eater (2014) Source.
As of 2023, working with DNS data is just going through a mish-mash of closed datasets/expensive APIs.
Some interesting usages:
The CIA really likes this registrar, e.g.:
Some cool ones:
  • playinside.me
https://web.archive.org/web/20230509123836im_/https://i.kym-cdn.com/entries/icons/original/000/033/037/girl.jpg