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 .NET Signature:

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

User-Defined Types:

[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;
}

//used for level of indirection and to pass null
[StructLayout(LayoutKind.Sequential)]
public class GuidClass
{
    public Guid DomainGuid;
}

Notes:

Pointer to a PDOMAIN_CONTROLLER_INFO value that receives a pointer to a DOMAIN_CONTROLLER_INFO structure that contains data about the domain controller selected. This structure is allocated by DsGetDcName. The caller must free the structure using the NetApiBufferFree function when it is no longer required.

Tips & Tricks:

Please add some!

Sample Code:

private DOMAIN_CONTROLLER_INFO GetDomainInfo()
{
    DOMAIN_CONTROLLER_INFO domainInfo;
    IntPtr pDCI = IntPtr.Zero;

    try
    {
        int val = DsGetDcName(null, null, null, null, 0, out pDCI);

        //check return value for error
        if(ERROR_SUCCESS == val)
        {
            domainInfo = (DOMAIN_CONTROLLER_INFO)Marshal.PtrToStructure(pDCI, typeof(DOMAIN_CONTROLLER_INFO));
        }
        else
        {
            throw new Win32Exception(val);
        }
    }
    finally
    {
        NetApiBufferFree(pDCI);
    }
    return domainInfo;
}

Alternative Managed API:

TODO