Question

I would like to have a quick script listing all active hosts in a LAN, and I am a bit lost. From other posts I figured that this can be done most effectively by polling the DHCP server (in my case a Lancom router) using SNMP.

However, I am not familiar with the SNMP commands in PHP. Is snmpwalk() the correct function? Can I get snmpwalk() or any other php function to return an array that contains a list of all live hosts?

Answer 1

So I wrote a script that probes the Lancom router and pulls out the DHCP/BOOTP table. It may be used for all those who need to monitor such routers, and therefore I am sharing it. It also outputs a nice HTML table; the function BetterTable() can be used on any 2D array.

You will need to set IP, userid, and pwd (first three variables) in order to use the script on your router.

    <?php

    $router_ip = '';
    $username = '';
    $password = '';
    $port = 23;
    $timeout = 10;

    $connection = fsockopen($router_ip, $port, $errno, $errstr, $timeout);

    if(!$connection){
     echo "Connection failed\n";
     exit();
    } else {

     fputs($connection, "$username\r\n");
     fputs($connection, "$password\r\n");
     fputs($connection, "cd setup/dhcp/dhcp-table \r\n");
     fputs($connection, "dir \r\n");
     fputs($connection, " ");

     $j = 0;
     while ($j < 16) {
      fgets($connection);
      $j++;
     }
     stream_set_timeout($connection, 2);
     $timeoutCount = 0;
     $content ='';
     $DhcpArray = '';
     (int) $index =0;

    $DhcpFile = "C:\IP-Symcon\webfront\user\images\LancomDhcp.txt";
    $fh = fopen($DhcpFile, 'w') or die("can't open file");

    //$DhcpArray[0] = array ('IP-Address', 'MAC-Address', 'Timeout', 'Hostname', 'Type', 'LAN-Ifc', 'Ethernet-Port', 'VLAN-ID', 'Network-Name');

     while (!feof($connection)){

      $content = fgets($connection);
      $content = str_replace("\r", '', $content);
      $content = str_replace("\n", "", $content);
      $lineArray = explode(' ', $content); 
      if (isValidIp($lineArray [0]))
          { 
          $DhcpArray[$index]['IP-Address'] = substr ($content, 0,17);
          $DhcpArray[$index]['MAC-Address'] = substr ($content, 17,32-18);
          $DhcpArray[$index]['Timeout'] = substr ($content, 31,41-32);
          $DhcpArray[$index]['Hostname'] = substr ($content, 40,108-41);
          $DhcpArray[$index]['Type'] = substr ($content, 107,125-108);
          $DhcpArray[$index]['LAN-Ifc'] = substr ($content, 124,137-125);
          $DhcpArray[$index]['Ethernet-Port'] = substr ($content, 136,152-137);
          $DhcpArray[$index]['VLAN-ID'] = substr ($content, 151,161-152);
          $DhcpArray[$index]['Network-Name'] = substr ($content, 160);
          fwrite($fh, $content);
          $index +=1;
          }

      # If the router say "press space for more", send space char:
      if (preg_match('/MORE/', $content) ){ // IF current line contain --More-- expression,
       fputs ($connection, " "); // sending space char for next part of output.
      } # The "more" controlling part complated.

      $info = stream_get_meta_data($connection);
      if ($info['timed_out']) { // If timeout of connection info has got a value, the router not returning a output.
       $timeoutCount++; // We want to count, how many times repeating.
      }
      if ($timeoutCount >2){ // If repeating more than 2 times,
       break;   // the connection terminating..
      }
     }
     $content = substr($content,410);

     BetterTable($DhcpArray);




    fclose($fh);

    }
    echo "End.\r\n";

    //--------------------------------------------------------------------

    function isValidIp($ip)
    {/* PCRE Pattern written by Junaid Atari */
        return !preg_match ( '/^([1-9]\d|1\d{0,2}|2[0-5]{2})\.('.
                             '(0|1?\d{0,2}|2[0-5]{2})\.){2}(0|1?'.
                             '\d{0,2}|2[0-5]{2})(\:\d{2,4})?$/',
                             (string) $ip )
                ? false
                : true;
    }

    //--------------------------------------------------------------

    function BetterTable($twoDimArray)
    {
    $i = 0;
    echo "<table>
            <table class='BetterTable' border='1'>";

    echo "<tr>";
    echo '<td>Line #
    </td>';
    foreach ($twoDimArray[0] as  $fieldName => $fieldValue)
        {
            echo '<td>'.$fieldName. '</td>';
        }echo '</tr>';
    $i = 0;

    foreach ($twoDimArray as $rowName => $rowValue) 
    {
            if ($i%2 == 0) 
                Echo "<tr bgcolor=\"#d0d0d0\" >";
            else 
                Echo "<tr bgcolor=\"#eeeeee\">";
        $fields = count($twoDimArray[$i]);
        $y = 0;
        echo '<td>'.$i. '</td>';
        foreach ($rowValue as  $fieldName => $fieldValue)
        {
            echo '<td>'.$fieldValue. '</td>';
            $y = $y + 1;
        }
        echo '</tr>';
        $i = $i + 1;
    }


    echo '</table>';
    }


    ?>