How to access the subdomain of an IP address in the browser?

Question

To get to the IP address of an example website, you just visit

subdomain.example.com 

However, if I try to visit

subdomain.2.1.33.111 (example ip) 

Firefox returns an error.
Why?

Answer 1

All browsers will return an error for this. The reason is that subdomains are part of the DNS (Domain Name Service) system, where IP addresses are related to the underlying IP protocol.

The best way to think of this relationship is that domains (including subdomains) are human-readable labels which DNS then allows you to point to IP addresses. It would not be very catchy to have an IP address as your website on a TV ad, for example.

There is much more detail on DNS and IP addresses if you want to delve into more detail than this.