Host names and URL syntax

Question

I have done some reading on proper Hostname syntax and can't figure out what is a really proper Hostname/URL syntax Can you please tell me if the following URLs are syntactically correct?

1.2.3.4.5.6.7/something
10.123.143.13333/something
1.2.3.4.5.6.7.com/something
some.host.name.com.org/something

Those are just some examples that i couldn't figure out. Are those URLs correct?

Answer 1

These are not URLs, as they are missing a scheme.

Assuming that you mean HTTP URLs, they would be:

http://1.2.3.4.5.6.7/something
http://10.123.143.13333/something
http://1.2.3.4.5.6.7.com/something
http://some.host.name.com.org/something

RFC 3986 defines the syntax of the host subcomponent for all URIs (and RFC 2616 for HTTP(S) URIs follows that).

The host names of your example URIs would be:

1.2.3.4.5.6.7
10.123.143.13333
1.2.3.4.5.6.7.com
some.host.name.com.org

Valid host names follow the syntax defined (in the section linked above) by IP-literal, IPv4address, or reg-name:

1. Check if IP-literal:

As an IP-literal requires enclosing square brackets ([…]), none are IP-literal host names.

2. Check if IPv4address:

As an IPv4address must contain exactly three . characters, 1.2.3.4.5.6.7, 1.2.3.4.5.6.7.com, and some.host.name.com.org can’t be IPv4address host names.

While 10.123.143.13333 has three ., "13333" is not a valid dec-octet, so it’s not an IPv4address.

3. Check if reg-name:

All of your examples are valid reg-name host names, as 0-9, a-z, and . are allowed characters.

Note that this does not mean that these are valid domain names in the DNS. RFC 3986 "does not mandate a particular registered name lookup technology".