I didn't know about filter_var at the moment I tried to solve that problem. Now I would probably use something similar to your solution.

On a 32-bit system, depending on the ip address, a valid result might be negative due to integer overflow. Also, ip2long can work with incomplete IP addresses, so it should be used carefully (see: https://secure.php.net/manual/en/function.ip2long.php#115761)

Interesting solution. I wonder if you need the check for "255.255.255.255" though. When I run ip2long() on that, I get a valid result. Also, depending on the system, ip2long can work with incomplete IP addresses, so it should be used carefully (see: https://secure.php.net/manual/en/function.ip2long.php#115761)