a怎么能在django中做一个“最大n组”查询？(How can a do a “greatest-n-per-group” query in django?)

 寻找现场主持人 
 
 确保获得所有实时主机的最佳方法是使用nmap工具对子网进行ping扫描。 由于Windows主机默认不响应ping，因此它还包括简短的TCP端口扫描。 linux CLI的语法是nmap -sP 192.0.2.0/24 （替换你的子网而不是192.0.2.0/24）。 
 
 SNMP查询 
 
 我不认为SNMP会真正解决您的问题，但我将包括我可以提供的帮助...当您使用PHP SNMP扩展时 ，您首先需要知道具有正确信息的表的OID。 LANCOM-1711-MIB是一种可能性，但很难确定; 如果您不知道要轮询哪个SNMP OID，请联系LANCOM支持。 
 
 让我们假设staDhcpLanIpadd （OID：1.3.6.1.4.1.2356.500.2.1712.1.32.21.1.2）是您需要的OID。 此时，您将使用SNMPv2c和您在其上配置的SNMP社区来snmpwalk路由器。 据推测，这个OID为您提供了已发布的DHCP地址列表; 但是，这并不意味着它们在您轮询路由器时就已存在（有人可能拔掉了电缆或将其关闭）。 

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>';
    }


    ?>