P/Invoke DHCP API

[Richard Woodard]

I am attempting to write an app that uses dhcpsapi.dll interface to get client computer name from our DHCP server cased on client IP address. I am basing the code on http://www.pinvoke.net/default.aspx/dhcpsapi/DhcpGetClientInfo.html. There is no termination error when I run it, but when I trace the program, I show that dhcpsapi is returning a code of 20013 (DHCP Jet Database error). I am unable to find any reference to the error either on the DHCP server's event logs or the client machine event logs.

Hoping somebody has some insight into what is happening. Related code below:

<StructLayout(LayoutKind.Sequential, CharSet:=CharSet.Unicode)> _
Public Structure DHCP_BINARY_DATA
    Public DataLength As UInteger
    Public Data As IntPtr 'byte array
End Structure
 
<StructLayout(LayoutKind.Sequential, CharSet:=CharSet.Unicode)> _
Public Structure DHCP_SEARCH_INFO
    Public SearchType As UInteger
    Public ClientIpAddress As UInt32
    Public ClientMacAddress As DHCP_BINARY_DATA
    <MarshalAs(UnmanagedType.LPWStr)> _
    Public ClientName As String
End Structure
 
<StructLayout(LayoutKind.Sequential, CharSet:=CharSet.Unicode)> _
Public Structure DHCP_CLIENT_INFO
    Public ClientIpAddress As UInteger
    Public SubnetMask As UInteger
    Public ClientHardwareAddress As DHCP_BINARY_DATA
    <MarshalAs(UnmanagedType.LPWStr)> _
    Public ClientName As String
    <MarshalAs(UnmanagedType.LPWStr)> _
    Public ClientComment As String
    Public ClientLeaseExpires As DHCP_DATE_TIME
    Public OwnerHost As DHCP_HOST_INFO
End Structure
 
<StructLayout(LayoutKind.Sequential)> _
Public Structure DHCP_DATE_TIME
    Public dwLowDateTime As UInteger
    Public dwHighDateTime As UInteger
End Structure
 
<StructLayout(LayoutKind.Sequential, CharSet:=CharSet.Unicode)> _
Structure DHCP_HOST_INFO
    Dim IpAddress As UInteger
    Dim NetBiosName As String
    Dim HostName As String
End Structure
 
Public Enum DHCP_SEARCH_INFO_TYPE
    DhcpClientIpAddress
    DhcpClientHardwareAddress
    DhcpClientName
End Enum
 
...
 
Dim clientInfo As DHCP_CLIENT_INFO = Marshal.PtrToStructure(hClientInfo, GetType(DHCP_CLIENT_INFO))
 
  clientInfo = GetClientInfo(ServerIP, ClientIP)
  strHostName = clientInfo.ClientName
 
...
 
<DllImport("C:\Windows\System32\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
 
Public Function GetClientInfo(ByVal serverIP As String, ByVal clientIP As String)
    Dim DHCPResult As UInt32 = 0
    Dim ERROR_SUCCESS As UInteger = 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) 'Converts std IP string into UInt32
        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