pinvoke.net: Edit: dhcpsapi.DhcpGetClientInfo

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Summary: The DhcpGetClientInfo function returns information about a specific DHCP client.

!!!!C# Signature:
 /// <summary>
 /// The DhcpGetClientInfo function returns information about a specific DHCP client.
 /// </summary>
 /// <param name="ServerIpAddress">[in] Unicode string that specifies the IP address of the DHCP server.</param>
 /// <param name="SearchInfo">[in] DHCP_SEARCH_INFO structure that contains the parameters for the search. </param>
 /// <param name="ClientInfo">[out] Pointer to a DHCP_CLIENT_INFO structure that contains information describing the DHCP client that most closely matches the provided search parameters. If no client is found, this parameter will be null.</param>
 /// <returns>This function returns ERROR_SUCCESS upon a successful call. Otherwise, it returns one of the DHCP Server Management API Error Codes.</returns>
 [DllImport("dhcpsapi.dll")]
 static extern UInt32 DhcpGetClientInfo(
   [MarshalAs(UnmanagedType.LPWStr)]
   String ServerIpAddress,
   ref DHCP_CLIENT_SEARCH_IP_ADDRESS si,
   out IntPtr ci);

!!!!VB Signature:
         ''' <summary> 
        ''' The DhcpGetClientInfo function returns information about a specific DHCP client. 
        ''' </summary> 
        ''' <param name="ServerIpAddress">[in] Unicode string that specifies the IP address of the DHCP server.
        ''' </param> 
        ''' <param name="SearchInfo">[in] DHCP_SEARCH_INFO structure that contains the parameters for the search. 
        ''' </param> 
        ''' <param name="ClientInfo">[out] Pointer to a DHCP_CLIENT_INFO structure that contains information describing the DHCP client that most closely matches the provided search parameters. If no client is found, this parameter will be null.
        ''' </param> 
        ''' <returns>This function returns ERROR_SUCCESS upon a successful call. Otherwise, it returns one of the DHCP Server Management API Error Codes.
        ''' </returns> 
        <DllImport("dhcpsapi.dll", SetLastError:=True, CharSet:=CharSet.Unicode)> _
        Public Shared Function DhcpGetClientInfo( _
            ByVal ServerIpAddress As String, _
            ByRef SearchInfo As DHCP_SEARCH_INFO, _
            ByRef ClientInfo As IntPtr) As UInt32
        End Function

!!!!User-Defined Types:
[DHCP_SEARCH_INFO], [DHCP_CLIENT_SEARCH_IP_ADDRESS]

!!!!Alternative Managed API:
Do you know one?  Please contribute it!

!!!!Notes:
VB Signature and sample code added by BlUNt, adapted from C# Samples

!!!!Tips & Tricks:

Completed library DHCP functions.

http://www.rupj.net/portfolio/dhcp-web-services.html

!!!!Sample VB Code:

Public Function GetClientInfo(ByVal serverIP As String, ByVal clientIP As String)
            Dim DHCPResult As UInt32 = 0
            Try
                Dim searchInfo As New DHCP_SEARCH_INFO
                Dim searchInfoType As DHCP_SEARCH_INFO_TYPE = DHCP_SEARCH_INFO_TYPE.DhcpClientIpAddress
                searchInfo.SearchType = searchInfoType
                searchInfo.ClientIpAddress = ConvertIPAddress(clientIP)
                Dim hClientInfo As IntPtr

DHCPResult = DhcpGetClientInfo(serverIP, searchInfo, hClientInfo)

If DHCPResult = ERROR_SUCCESS And Not hClientInfo = IntPtr.Zero Then
                    Dim clientInfo As DHCP_CLIENT_INFO = Marshal.PtrToStructure(hClientInfo, GetType(DHCP_CLIENT_INFO))
                    Return clientInfo
                End If
                Return Nothing
            Catch ex As Exception
                Console.WriteLine(ex.Message)
                Return Nothing
            End Try
        End Function

Public Shared Function ConvertIPAddress(ByVal ipAddress As String) As UInt32
            Dim dot As Char() = ".".ToCharArray()
            Dim zero As Char() = "0".ToCharArray()
            Dim Octets As String() = ipAddress.Split(dot(0))
            Dim HexIP As String = ""

For Each Octet As String In Octets
                HexIP += Convert.ToString(Convert.ToInt16(Octet), 16).PadLeft(2, zero(0))
            Next
            Return Convert.ToUInt32(HexIP, 16)
        End Function

!!!!Sample Code:
 static void Main()
        {
            String ServerIpAddress = "192.168.0.250";

UInt32 DHCPResult = 0;
            try
            {
 
                DHCP_SEARCH_INFO searchInfo = new DHCP_SEARCH_INFO();
                DHCP_SEARCH_INFO_TYPE searchInfoType = DHCP_SEARCH_INFO_TYPE.DhcpClientIpAddress;

searchInfo.SearchType = searchInfoType;
                searchInfo.ClientIpAddress = ConvertIPAddress("192.168.0.10");

IntPtr pClientInfo;
                DHCPResult = DhcpGetClientInfo(ServerIpAddress, ref searchInfo, out pClientInfo);
                if (DHCPResult == 0 && pClientInfo != IntPtr.Zero)
                {
                    DHCP_CLIENT_INFO clientInfo = (DHCP_CLIENT_INFO)Marshal.PtrToStructure(pClientInfo, typeof(DHCP_CLIENT_INFO));
                    Console.WriteLine(DHCPResult.ToString() + " Client Info: " + clientInfo.ClientName);
                }
                else
                {
                    Console.WriteLine(DHCPResult.ToString() + " Failed");
                }
        }

public static UInt32 ConvertIPAddress(string ipAddress)
        {
            char[] dot = ".".ToCharArray();
            char[] zero = "0".ToCharArray();
            string[] Octets = ipAddress.Split(dot[0]);
            string HexIP = "";

foreach (string Octet in Octets)
            {
                HexIP += Convert.ToString(Convert.ToInt16(Octet), 16).PadLeft(2, zero[0]);
            }
            return Convert.ToUInt32(HexIP, 16);
        }

!!!!C# Sample for getting a MAC-Address to a specified IP
 public string GetClientInfoByIp(string server, string client)
 { 
 	DHCP_CLIENT_SEARCH_IP_ADDRESS si = new DHCP_CLIENT_SEARCH_IP_ADDRESS(); 
	si.SearchType = (int)DHCP_SEARCH_INFO_TYPE.DhcpClientIpAddress ;
	si.ClientIpAddress = StringIPAddressToUint32(client);

UInt32 res = 0;
	try
	{
		IntPtr oInfo;
		res = DhcpGetClientInfo(new String(server.ToCharArray()), ref si, out oInfo);

if (res == 0 && oInfo != IntPtr.Zero)
		{
			DHCP_CLIENT_INFO info = (DHCP_CLIENT_INFO)Marshal.PtrToStructure(oInfo, typeof(DHCP_CLIENT_INFO));
			String mac = String.Format("{0:x2}-{1:x2}-{2:x2}-{3:x2}-{4:x2}-{5:x2}",
				Marshal.ReadByte(info.ClientHardwareAddress.Data,0),
				Marshal.ReadByte(info.ClientHardwareAddress.Data,1),
				Marshal.ReadByte(info.ClientHardwareAddress.Data,2),
				Marshal.ReadByte(info.ClientHardwareAddress.Data,3),
				Marshal.ReadByte(info.ClientHardwareAddress.Data,4),
				Marshal.ReadByte(info.ClientHardwareAddress.Data,5));

return mac;
		} 
		else
		{
			Console.WriteLine("Failed!");
			return "00-00-00-00-00-00";
		}
	} 
	catch(Exception e)
	{
		Console.WriteLine(e);
		return "00-00-00-00-00-00";
	}
 }

public uint StringIPAddressToUint32(string ip_string)
 {
	IPAddress ipa = IPAddress.Parse(ip_string);
	byte[] ip_bytes = ipa.GetAddressBytes();

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

return ip_uint;
 }

static void Main()
 {
	String dhcpServerIP = "192.168.1.1";
	String clientIP = "182.168.1.120";
	
	Console.WriteLine("MAC-Adress for " + clientIp + " is " + GetClientInfoByIp(dhcpServerIP, clientIp));
 }

Documentation: DhcpGetClientInfo@msdn on MSDN