Matching an IP to a CIDR mask in PHP 5?

Question

I\'m looking for quick/simple method for matching a given IP4 dotted quad IP to a CIDR notation mask.

I have a bunch of IPs I need to see if they match a range of IP

Answer 1

I recently needed to match an IP address to a CIDR mask and came across this article. Below is a slightly different approach based on the ideas above and includes a check on the CIDR input. The function returns false if an incorrect CIDR format is submitted.

I posted this solution for anyone who needs a turn-key function that has been tested.

/**
 * Validates subnet specified by CIDR notation.of the form IP address followed by 
 * a '/' character and a decimal number specifying the length, in bits, of the subnet
 * mask or routing prefix (number from 0 to 32).
 *
 * @param $ip - IP address to check
 * @param $cidr - IP address range in CIDR notation for check
 * @return bool - true match found otherwise false
 */
function cidr_match($ip, $cidr) {
    $outcome = false;
    $pattern = '/^(([01]?\d?\d|2[0-4]\d|25[0-5])\.){3}([01]?\d?\d|2[0-4]\d|25[0-5])\/(\d{1}|[0-2]{1}\d{1}|3[0-2])$/';
    if (preg_match($pattern, $cidr)){
        list($subnet, $mask) = explode('/', $cidr);
        if (ip2long($ip) >> (32 - $mask) == ip2long($subnet) >> (32 - $mask)) {
            $outcome = true;
        }
    }
    return $outcome;
}

Test data is shown in the image below: