PHP function that anonymizes IP addresses like Google Analytics does (https://support.google.com/analytics/answer/2763052)

mask_ip.php

<?php

function mask_ip($ip) {
    if (filter_var($ip, FILTER_VALIDATE_IP, FILTER_FLAG_IPV4)) {
        $parts = explode('.', $ip);
        $parts[count($parts)-1] = '0';
        return implode('.', $parts);
    } else if (filter_var($ip, FILTER_VALIDATE_IP, FILTER_FLAG_IPV6)) {
        $parts = explode(':', $ip);
        $parts[count($parts)-1] = '0';
        return implode(':', $parts);
    } else {
        return $ip;
    }
}

echo mask_ip('8.8.4.4') . PHP_EOL;
echo mask_ip('54.239.26.128') . PHP_EOL;
echo mask_ip('2001:4860:4860::8888') . PHP_EOL;
echo mask_ip('2001:4860:4860:0:0:0:0:8844') . PHP_EOL;

Script output:

8.8.4.0
54.239.26.0
2001:4860:4860:0
2001:4860:4860:0:0:0:0:0