DsGetDcName

C# Signature:

[DllImport("Netapi32.dll", CharSet=CharSet.Auto, SetLastError=true)]
static extern int DsGetDcName
(
    [MarshalAs(UnmanagedType.LPTStr)]
    string ComputerName,
    [MarshalAs(UnmanagedType.LPTStr)]
    string DomainName,
    [In] GuidClass DomainGuid,
    [MarshalAs(UnmanagedType.LPTStr)]
    string SiteName,
    int Flags,
    out IntPtr pDOMAIN_CONTROLLER_INFO
);

VB Signature:

Declare Function DsGetDcName Lib "netapi32.dll" (TODO) As TODO

Sample Code:

[StructLayout(LayoutKind.Sequential, CharSet = CharSet.Unicode)]
  struct DOMAIN_CONTROLLER_INFO 
  {  
    [MarshalAs(UnmanagedType.LPTStr)]  
    public string DomainControllerName;
    [MarshalAs(UnmanagedType.LPTStr)]    
    public string DomainControllerAddress;
    public uint   DomainControllerAddressType;
    public Guid   DomainGuid;
    [MarshalAs(UnmanagedType.LPTStr)]    
    public string DomainName;
    [MarshalAs(UnmanagedType.LPTStr)]    
    public string DnsForestName;
    public uint   Flags;
    [MarshalAs(UnmanagedType.LPTStr)]    
    public string DcSiteName;
    [MarshalAs(UnmanagedType.LPTStr)]    
    public string ClientSiteName;
  }

[DllImport("Netapi32.dll", CharSet=CharSet.Auto, SetLastError=true)]        
  static extern int DsGetDcName  
  (
    [MarshalAs(UnmanagedType.LPTStr)]
    string ComputerName,
    [MarshalAs(UnmanagedType.LPTStr)]
    string DomainName,
    [In] int DomainGuid,
    [MarshalAs(UnmanagedType.LPTStr)]
    string SiteName,
    [MarshalAs(UnmanagedType.U4)]
    DSGETDCNAME_FLAGS flags,
    out IntPtr pDOMAIN_CONTROLLER_INFO
  );

  [DllImport("Netapi32.dll", SetLastError=true)]    
   static extern int NetApiBufferFree(IntPtr Buffer);

  [Flags]
  public enum DSGETDCNAME_FLAGS : uint
  {
    DS_FORCE_REDISCOVERY = 0x00000001,
    DS_DIRECTORY_SERVICE_REQUIRED = 0x00000010,
    DS_DIRECTORY_SERVICE_PREFERRED = 0x00000020,
    DS_GC_SERVER_REQUIRED = 0x00000040,
    DS_PDC_REQUIRED = 0x00000080,
    DS_BACKGROUND_ONLY = 0x00000100,
    DS_IP_REQUIRED = 0x00000200,
    DS_KDC_REQUIRED = 0x00000400,
    DS_TIMESERV_REQUIRED = 0x00000800,
    DS_WRITABLE_REQUIRED = 0x00001000,
    DS_GOOD_TIMESERV_PREFERRED = 0x00002000,
    DS_AVOID_SELF = 0x00004000,
    DS_ONLY_LDAP_NEEDED = 0x00008000,
    DS_IS_FLAT_NAME = 0x00010000,
    DS_IS_DNS_NAME = 0x00020000,
    DS_RETURN_DNS_NAME = 0x40000000,
    DS_RETURN_FLAT_NAME = 0x80000000
   }

   private DOMAIN_CONTROLLER_INFO GetDomainInfo()
   {
    DOMAIN_CONTROLLER_INFO domainInfo;
    const int ERROR_SUCCESS = 0;
    IntPtr pDCI = IntPtr.Zero;
    try
    {
     int val = DsGetDcName("","",0,"",
     DSGETDCNAME_FLAGS.DS_DIRECTORY_SERVICE_REQUIRED|
     DSGETDCNAME_FLAGS.DS_RETURN_DNS_NAME|
     DSGETDCNAME_FLAGS.DS_IP_REQUIRED, out pDCI);
       //check return value for error
       if(ERROR_SUCCESS == val)
       {
    domainInfo = (DOMAIN_CONTROLLER_INFO)Marshal.PtrToStructure(pDCI, typeof(DOMAIN_CONTROLLER_INFO));

    string msg = "Forest : " + domainInfo.DnsForestName  + "\r\n";
    msg += "DC-Site: " + domainInfo.DomainControllerName + "\r\n";
    msg += " Client: " + domainInfo.ClientSiteName + "\r\n";
    System.Windows.Forms.MessageBox.Show ( msg);
       }
    else
       {
     throw new Win32Exception(val);
       }
    }
  finally
  {
    NetApiBufferFree(pDCI);
  }
  return domainInfo;
}