Get the start and end IP from an IP Range by a CIDR (Classless Inter-Domain Routing) notation, complete or incomplete. As discussed here: https://blog.gerbenjacobs.nl/get-ip-range-by-cidr-notation.html

getIPRangeByCIDR.php

<?php

function getIPRangeByCIDR($cidr) {
    // Making sure IPs are valid
    $ipdata = explode('/', ltrim($cidr, '0'));
    $dotcount = substr_count($ipdata[0], '.');
    if ($dotcount != 3) {
        $ipdata[0] .= str_repeat('.0', (3-$dotcount));
    }
    $cidr_address = sprintf('%s/%s', $ipdata[0], $ipdata[1]);
	
    // By 'unknown' http://www.php.net/manual/en/ref.network.php#30910
    $first = substr($cidr_address, 0, strpos($cidr_address, "/"));
    $netmask = substr(strstr($cidr_address, "/"), 1);
 
    $first_bin = str_pad(decbin(ip2long($first)), 32, "0", STR_PAD_LEFT);
	$last_bin = '';
    $netmask_bin = str_pad(str_repeat("1", (integer)$netmask), 32, "0", STR_PAD_RIGHT);
 
    for ($i = 0; $i < 32; $i++) {
        if ($netmask_bin[$i] == "1")
            $last_bin .= $first_bin[$i];
        else
            $last_bin .= "1";
    }
 
    $last = long2ip(bindec($last_bin));
    return array($first, $last);
}

print_r(getIPRangeByCIDR('190.151.192/18')); 
// Array ( [0] => 190.151.192.0 [1] => 190.151.255.255 ) 

print_r(getIPRangeByCIDR('17/8')); 
// (Apple) Array ( [0] => 17.0.0.0 [1] => 17.255.255.255 ) 

print_r(getIPRangeByCIDR('65.192/11')); 
// (NSA?) Array ( [0] => 65.192.0.0 [1] => 65.223.255.255 )

?>