How do I check if a users input is a valid IP address or not?

Question

I want to check if an entered input is a valid IP address or not. I would like a specific function that will help me validate a users input.

Answer 1

By using preg_match();

function checkIPAddress($ipAddress) 
{
    return preg_match('/^(?:25[0-5]|2[0-4]\d|1\d\d|[1-9]\d|\d)(?:[.](?:25[0-5]|2[0-4]\d|1\d\d|[1-9]\d|\d)){3}$/', $ipAddress);
}

Answer 2

filter_var($ip, FILTER_VALIDATE_IP)

http://www.php.net/filter_var

Answer 3

// Usually you'd get the value from $_POST or $_GET
$ip = "10.3.1.5";
if(!filter_var($ip, FILTER_VALIDATE_IP)) {
   echo "Not a valid IP address!";
}

You can modify this by filtering for IPv4 and IPv6 IP addresses and exclude private and reserved IPs.

http://www.php.net/manual/filter.filters.validate.php