Deal with DHCP Server IP Exhausted

Recently, I have a problem with DHCP Server service run on Windows Server 2003 that use full ip address ranges, alot of IP used by strange mac address (3139…, longer than 12 charater) with type DHCP/BOOTP, even my DHCP server have mac address filter add-in and assign IP option is DHCP only. No special info in event log, Google return no clear root cause and solution.

Some strange address

this happen not just with Windows S2K3 also with S2K8 or 2012 too.

Before someone pointing out how we can fix this, I think I must live with it, here is my ideal and solution:

PHP code:

<?php
/**
 * Clean bad ip address leases
 * https://social.technet.microsoft.com/Forums/windowsserver/en-US/53a1e987-5d44-415e-8510-62cb1e58716a/weird-mac-on-dhcp-31202e3235332e302e?forum=winserverNIS
 * @param string $server_name, dhcp server name, ex: srv.domain.local
 * @param array $dhcp_scope, scopes by dhcp, ex: ['192.168.1.0']
 */
function cleanBadIpAdress($server_name, $dhcp_scope)
{
    if (!empty($dhcp_scope)) {
        foreach ($dhcp_scope as $scope) {
            $export_file_name = "{$server_name}.{$scope}.txt";
            // refresh address leases list
            exec("netsh dhcp server scope {$scope} initiate reconcile fix");
            echo "Refresh DHCP leases IP done" . PHP_EOL;
            // export address leases to file, in the same folder of php file
            exec("netsh dhcp server \\\\{$server_name} scope {$scope} show clients 1 > {$export_file_name}");
            echo "Export DHCP leases IP to file done" . PHP_EOL;
            // read file and find bad ip
            if (file_exists($export_file_name)) {
                $content = explode(PHP_EOL, file_get_contents($export_file_name));
                if (!empty($content)) {
                    foreach ($content as $line) {
                        $line = explode("  ", $line);
                        // $line[0] is IP address, $line[1] have subnet, $line[2] have mac address
                        // sometime $line[1] is emplty and $line[2] have subnet and $line[3] have mac address
                        $bad_ip = null;
                        if (isset($line[1]) && isset($line[2]) && strpos($line[1], '255.') !== false) {
                            if (strlen($line[2]) > 20) {
                                // found bad mac address
                                $bad_ip = $line[0];
                                echo "Found bad ip {$bad_ip}, mac address {$line[2]}" . PHP_EOL;
                            }
                        } elseif (isset($line[2]) && isset($line[3]) && strpos($line[2], '255.') !== false) {
                            if (strlen($line[3]) > 20) {
                                // found bad mac address
                                $bad_ip = $line[0];
                                echo "Found bad ip {$bad_ip}, mac address {$line[3]}" . PHP_EOL;
                            }
                        }

                        if ($bad_ip) {
                            // delete bad address
                            exec("netsh dhcp server scope {$scope} delete lease {$bad_ip}");
                            echo "Bad IP {$bad_ip} deleted" . PHP_EOL;
                        }
                    }
                }
                // delete exported file
                unlink($export_file_name);
            }
        }
    }
}
?>

You can see example code on Github here: https://github.com/NothingCtrl/DHCP-Clean-Bad-Leases-IP

Hope this help.

Origin post at https://archive.camratus.com/2017/07/26/deal-with-dhcp-server-ip-exhausted/

Tags:
#php #dhcp #windows #winddows-server