That's remarkable to me - I feel like my internet life hasn't been so sheltered not to come across this before, but it also feels so obvious in retrospect. Do share some examples if you don't mind.
There are undoubtedly many, many more examples across the internet. FTP servers, along with HTTP mirrors of those FTP servers are some obvious examples where hostnames are often not required.
There seems to a web developer-driven, cargo cult mentality against use of IP addresses, but AFAICT search engines do not try to hide IP addresses; I sometimes get them in SERPS.
Historically IP addresses were supported in smtpd software, too. For example, qmail still supports IP addresses, if enclosed in brackets.
But here's two more easy examples, InterNIC and NetBSD.
https://192.0.32.9
https://192.0.32.9/domain/root.zone
https://199.233.217.201/pub/
There are undoubtedly many, many more examples across the internet. FTP servers, along with HTTP mirrors of those FTP servers are some obvious examples where hostnames are often not required.
There seems to a web developer-driven, cargo cult mentality against use of IP addresses, but AFAICT search engines do not try to hide IP addresses; I sometimes get them in SERPS.
Historically IP addresses were supported in smtpd software, too. For example, qmail still supports IP addresses, if enclosed in brackets.