It's a particularly cursed form of writing IPv4 addresses:

> A popular implementation of IP networking, originating in 4.2BSD, contains a function inet_aton() for converting IP addresses in character string representation to internal binary storage. In addition to the basic four-decimals format and 32-bit numbers, it also supported intermediate syntax forms of octet.24bits (e.g. 10.1234567; for Class A addresses) and octet.octet.16bits (e.g. 172.16.12345; for Class B addresses). It also allowed the numbers to be written in hexadecimal and octal representations, by prefixing them with 0x and 0, respectively. These features continue to be supported in some software, even though they are considered as non-standard.

(https://en.wikipedia.org/wiki/Dot-decimal_notation#IPv4_addr...)

Never use this.

127.1 is the same as 127.0.0.1. 0 bytes are inserted based on the following:

  x     -> 0.0.0.x
  x.y   -> x.0.0.y
  x.y.z -> x.y.0.z

little known fact: you can write shorthand for any ip address. It simply omits 0. Ie 127.0.0.1 (or 127.000.000.001). Try pinging it. `ping 127.1`

10.0.0.3 -> ping 10.3

what's the problem, there's a self hosted web server on it.

If you are talking about the short url, well ipv4 allows it and they needed to save space to fit on the floppy ;)