calculate IP range using PHP and CIDR

Question

I\'ve seen various questions and answers around this site and I\'m still having difficulty wrapping my head around this problem (could be because I\'ve got a cold). Regardle

Answer 1

As you've already noted, all IPv4 addresses can be converted to numbers using ip2long(), and converted back using long2ip(). The critical extra bit I'm not sure you've noticed is that sequential IPs correspond with sequential numbers, so you can manipulate these numbers!

Given a CIDR prefix (e.g, $prefix = 30 for your range), you can calculate the number of IPs in that range using a bit shift operator:

$ip_count = 1 << (32 - $prefix);

And then loop through all the IPs in that range using:

$start = ip2long($start_ip);
for ($i = 0; $i < $ip_count; $i++) {
    $ip = long2ip($start + $i);
    // do stuff with $ip...
}