Abfragen von einen DHCP-server in C#

using System;
using System.Runtime.InteropServices;
using System.Collections;
using System.Net;

namespace dhcp
{
//c# class for processed clients

public class dhcpClient
{
    public string hostname { get; set; }
    public string ip       { get; set; }
    public string mac      { get; set; }
}

//structs for use with call to unmanaged code

[StructLayout(LayoutKind.Sequential)]
public struct DHCP_CLIENT_INFO_ARRAY
{
    public uint NumElements;
    public IntPtr Clients;
}

[StructLayout(LayoutKind.Sequential)]
public struct DHCP_CLIENT_UID
{
    public uint DataLength;
    public IntPtr Data;
}

[StructLayout(LayoutKind.Sequential, CharSet = CharSet.Auto)]
public struct DHCP_CLIENT_INFO
{
    public uint ip;
    public uint subnet;

    public DHCP_CLIENT_UID mac;

    [MarshalAs(UnmanagedType.LPWStr)]
    public string ClientName;

    [MarshalAs(UnmanagedType.LPWStr)]
    public string ClientComment;
}

//main

class Program
{
    static void Main()
    {
        try
        {
            //get settings

            String server, subnet;

            Console.Write("Enter server : ");
            server = Console.ReadLine();
            Console.Write("Enter subnet : ");
            subnet = Console.ReadLine();

            //gather clients

            ArrayList clients = findDhcpClients(server, subnet);

            //output results

            Console.WriteLine();

            foreach (dhcpClient d in clients)
                Console.WriteLine(String.Format("{0,-35} {1,-15} {2,-15}", d.hostname, d.ip, d.mac));

            Console.WriteLine('\n' + clients.Count.ToString() + " lease(s) in total");
        }

        catch (Exception e)
        {
            Console.WriteLine(e.ToString());
        }

        Console.ReadLine();
    }

    static ArrayList findDhcpClients(string server, string subnet)
    {
        //set up container for processed clients

        ArrayList foundClients = new ArrayList();

        //make call to unmanaged code

        uint parsedMask     = StringIPAddressToUInt32(subnet);
        uint resumeHandle   = 0;
        uint numClientsRead = 0;
        uint totalClients   = 0;

        IntPtr info_array_ptr;

        uint response = DhcpEnumSubnetClients(
            server,
            parsedMask,
            ref resumeHandle,
            65536,
            out info_array_ptr,
            ref numClientsRead,
            ref totalClients
            );

        //set up client array casted to a DHCP_CLIENT_INFO_ARRAY
        //using the pointer from the response object above

        DHCP_CLIENT_INFO_ARRAY rawClients =
            (DHCP_CLIENT_INFO_ARRAY)Marshal.PtrToStructure(info_array_ptr, typeof(DHCP_CLIENT_INFO_ARRAY));

        //loop through the clients structure inside rawClients 
        //adding to the dchpClient collection

        IntPtr current = rawClients.Clients;

        for (int i = 0; i < (int)rawClients.NumElements; i++)
        {
            //1. Create machine object using the struct

            DHCP_CLIENT_INFO rawMachine =
                (DHCP_CLIENT_INFO)Marshal.PtrToStructure(Marshal.ReadIntPtr(current), typeof(DHCP_CLIENT_INFO));

            //2. create new C# dhcpClient object and add to the 
            //collection (for hassle-free use elsewhere!!)

            dhcpClient thisClient = new dhcpClient();

            thisClient.ip = UInt32IPAddressToString(rawMachine.ip);

            thisClient.hostname = rawMachine.ClientName;

            thisClient.mac = String.Format("{0:x2}{1:x2}.{2:x2}{3:x2}.{4:x2}{5:x2}",
                Marshal.ReadByte(rawMachine.mac.Data),
                Marshal.ReadByte(rawMachine.mac.Data, 1),
                Marshal.ReadByte(rawMachine.mac.Data, 2),
                Marshal.ReadByte(rawMachine.mac.Data, 3),
                Marshal.ReadByte(rawMachine.mac.Data, 4),
                Marshal.ReadByte(rawMachine.mac.Data, 5));

            foundClients.Add(thisClient);

            //3. move pointer to next machine

            current = (IntPtr)((int)current + (int)Marshal.SizeOf(typeof(IntPtr)));
        }

        return foundClients;
    }

    public static uint StringIPAddressToUInt32(string ip)
    {
        //convert string IP to uint IP e.g. "1.2.3.4" -> 16909060

        IPAddress i = System.Net.IPAddress.Parse(ip);
        byte[] ipByteArray = i.GetAddressBytes();

        uint ipUint = (uint)ipByteArray[0] << 24;
        ipUint += (uint)ipByteArray[1] << 16;
        ipUint += (uint)ipByteArray[2] << 8;
        ipUint += (uint)ipByteArray[3];

        return ipUint;
    }

    public static string UInt32IPAddressToString(uint ip)
    {
        //convert uint IP to string IP e.g. 16909060 -> "1.2.3.4"

        IPAddress i = new IPAddress(ip);
        string[] ipArray = i.ToString().Split('.');

        return ipArray[3] + "." + ipArray[2] + "." + ipArray[1] + "." + ipArray[0];
    }

    [DllImport("dhcpsapi.dll", SetLastError = true, CharSet = CharSet.Auto)]
    public static extern uint DhcpEnumSubnetClients(
            string ServerIpAddress,
            uint SubnetAddress,
        ref uint ResumeHandle,
            uint PreferredMaximum,
        out IntPtr ClientInfo,
        ref uint ElementsRead,
        ref uint ElementsTotal
    );
}
}