typedef ULONG NET_IFINDEX;
typedef ULONG NETIO_STATUS;

typedef union _NET_LUID
{
	ULONG64 Value;
	
	struct
	{
		ULONG64 Reserved     : 24;
		ULONG64 NetLuidIndex : 24;
		ULONG64 IfType       : 16;
	} Info;
} NET_LUID,  *PNET_LUID;

typedef NETIO_STATUS (WINAPI * ConvertInterfaceIndexToLuidProc)(
	NET_IFINDEX InterfaceIndex,
	PNET_LUID   InterfaceLuid
	);

//
// Suspected prototype of NsiGetParameter, via reverse engineering.
//

typedef DWORD (__stdcall * NsiGetParameterProc)(
	DWORD        Unknown0,        // 0x1
	CONST UCHAR* NpiId,           // 0x14 bytes for us
	DWORD        Unknown1,        // 0x7
	PNET_LUID    NetLuid,         // Interface LUID
	DWORD        LuidLength,      // Length of LUID
	DWORD        Unknown2,        // 0x0
	PUCHAR       OutputBuf,       // IF metric for LUID
	DWORD        OutputLength,    // sizeof(DWORD)
	DWORD        Unknown3         // 0x1c
	);

/*
 0:000> db NPI_MS_IPV4_MODULEID l14
 751b3364  18 00 00 00 01 00 00 00-00 4a 00 eb 1a 9b d4 11
 751b3374  91 23 00 50 04 77 59 BC                        
 */

const unsigned char NPI_MS_IPV4_MODULEID[0x18] =
{
	0x18, 0x00, 0x00, 0x00, 0x01, 0x00, 0x00, 0x00, 0x00, 0x4A, 0x00, 0xEB, 0x1A, 0x9B, 0xD4, 0x11,
	0x91, 0x23, 0x00, 0x50, 0x04, 0x77, 0x59, 0xBC
};

//
// Determine the "interface metric", or the lowest metric permissible on an
// interface.
//

DWORD
GetInterfaceMetric(
	__in DWORD           InterfaceIndex,
	__out __deref PDWORD InterfaceMetric
	)
{
	NET_LUID Luid;
	HMODULE  Nsi, Iphlpapi;
	DWORD    Status;

	ConvertInterfaceIndexToLuidProc _ConvertInterfaceIndexToLuid;
	NsiGetParameterProc             _NsiGetParameter;

	//
	// Set InterfaceMetric to zero.  This is the acceptable value for pre-Vista
	// systems.
	//

	*InterfaceMetric = 0;

	do
	{
		//
		// We'll need access to iphlpapi.dll for ConvertInterfaceIndexToLuid.
		//

		Iphlpapi = LoadLibraryW(L"Iphlpapi.dll");

		if (!Iphlpapi)
		{
			Status = GetLastError();
			break;
		}

		//
		// Try to load Nsi.dll, which is only present on Vista and later.
		//

		Nsi = LoadLibraryW(L"Nsi.dll");

		if (!Nsi)
		{
			Status = GetLastError();
			break;
		}

		//
		// Resolve entrypoints in Iphlpapi and Nsi.
		//

		_ConvertInterfaceIndexToLuid = (ConvertInterfaceIndexToLuidProc)GetProcAddress(Iphlpapi,
			"ConvertInterfaceIndexToLuid");

		if (!_ConvertInterfaceIndexToLuid)
		{
			Status = GetLastError();
			break;
		}

		_NsiGetParameter = (NsiGetParameterProc)GetProcAddress(Nsi,
			"NsiGetParameter");

		if (!_NsiGetParameter)
		{
			Status = GetLastError();
			break;
		}

		Status = _ConvertInterfaceIndexToLuid(InterfaceIndex,
			&Luid);

		if (Status != NO_ERROR)
			break;

		Status = _NsiGetParameter(0x01,
			NPI_MS_IPV4_MODULEID,
			0x07,
			&Luid,
			sizeof(Luid),
			0,
			(PUCHAR)InterfaceMetric,
			sizeof(*InterfaceMetric),
			0x1C);

		if (Status != NO_ERROR)
			break;
	} while(0) ;

	if (Nsi)
		FreeLibrary(Nsi);

	if (Iphlpapi)
		FreeLibrary(Iphlpapi);

	return Status;
}