Checking if a POST[] variable is an IP address?

Question

I'm making a script, in which the user needs to enter a valid IP address. How can I check that it's a valid IP address? (Doesn't need to resolve)

Basically $_POST['ip'] just needs to be between 0.0.0.0 and 255.255.255.255

Answer 1

1. Split your "IP" string by "."
2. Verify that there are four entries (octet) in the array.
3. Verify: 0 <= octet <= 255
4. If you want to get fancier, you can check that the IP isn't in a private network, isn't a multicast network, or isn't in the reserved space.

Edit: Use the built in PHP method if available! :)

Answer 2

If you're running PHP >= 5.2, use the Filter extension:

filter_var($ip, FILTER_VALIDATE_IP)

More info here and here.

Answer 3

You could also try preg_match(/^(?:(?:25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)\.){3}(?:25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)$/, $_POST['ip']).

More about preg_match() here

Also there are many patterns for validation. Choose most suitable one for you.

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Update: Also about using filters. Not all servers have already PHP equal or higher, than 5.2.0. So u can check version before using them, but IMHO most logical ways would be Filters or PCRE.