How does only numbers in URL resolve to a domain?

Question

I've been seeing some examples such as http://38263628 that resolves to a legitimate website https://example.com

When doing dig or nslookup on 38263628, it returns me NXDOMAIN.

How does the redirection or resolution work?

For data protection reasons, I can't give the actual numbers and domain it resolves to.

Thanks!

Answer 1

We usually write IP addresses as four dot-separated numbers like 12.34.56.78 but the address is just a number and it can be written in other ways. For example, 12.34.56.78 can also be written as 12.34.14414 or 12.2242638 or 203569230 or 0xc22384e or 0xc.0x22.0x38.0x4e.

The four-dot-separated form is effectively a base-256 representation of the number, so to convert from a single large number N into the four-dot-separated form A.B.C.D you would calculate these four values:

A = N / 256 / 256 / 256
B = N / 256 / 256 % 256
C = N / 256 % 256
D = N % 256

So your 38263628 is equivalent to 2.71.219.76

dig and nslookup don't work with plain numbers because they treat their arguments as strings, even when the arguments are known to represent IP addresses. (For instance, man dig says that the -x option requires an address in the four-dot form. That's because dig just wants to treat it as a string that can be split on the dots and rearranged into a in-addr.arpa query.)

However, most commands that convert their arguments into actual IP address numbers will accept any of the number formats. Try it with ping (which will helpfully show the address in four-dot format when it shows its results):

$ ping 203569230
PING 203569230 (12.34.56.78): 56 data bytes
...

That also gives you an easy way to convert any number into four-dot form -- just give the number as an argument to ping and let it do the conversion for you.