How to get the NETBIOS Domain Name using the FQDN in a Complex Environment

Question

Getting the NETBIOS domain name from a fully qualified Active Directory domain name is sometimes a tedious task. I found a good answer here.

In an environment with multi

Answer 1

You can also use the DsGetDcName API, which will do all the monkeying around for you. It will also cache calls and not even hit the network if the domain you are querying is the local computer.

If you have additional requirements on the capabilities of the

Use:

internal static string GetNetbiosNameForDomain(string dns)
{
    IntPtr pDomainInfo;
    int result = DsGetDcName(null, dns, IntPtr.Zero, null,
        DSGETDCNAME_FLAGS.DS_IS_DNS_NAME | DSGETDCNAME_FLAGS.DS_RETURN_FLAT_NAME,
        out pDomainInfo);
    try
    {
        if (result != ERROR_SUCCESS)
            throw new Win32Exception(result);

        var dcinfo = new DomainControllerInfo();
        Marshal.PtrToStructure(pDomainInfo, dcinfo);

        return dcinfo.DomainName;
    }
    finally
    {
        if (pDomainInfo != IntPtr.Zero)
            NetApiBufferFree(pDomainInfo);
    }
}

P/Invoke:

[StructLayout(LayoutKind.Sequential, CharSet = CharSet.Unicode)]
private class DomainControllerInfo
{
    public string DomainControllerName;
    public string DomainControllerAddress;
    public int DomainControllerAddressType;
    public Guid DomainGuid;
    public string DomainName;
    public string DnsForestName;
    public int Flags;
    public string DcSiteName;
    public string ClientSiteName;
}

[Flags]
private 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
}

[DllImport("Netapi32.dll", CallingConvention = CallingConvention.StdCall, EntryPoint = "DsGetDcNameW", CharSet = CharSet.Unicode)]
private static extern int DsGetDcName(
    [In] string computerName,
    [In] string domainName,
    [In] IntPtr domainGuid,
    [In] string siteName,
    [In] DSGETDCNAME_FLAGS flags,
    [Out] out IntPtr domainControllerInfo);

[DllImport("Netapi32.dll")]
private static extern int NetApiBufferFree(
    [In] IntPtr buffer);

private const int ERROR_SUCCESS = 0;