How to disable loopback packets in NDIS protocol driver

Question

How do I disable receiving loopback packets in protocol driver? The scenario is, my protocol driver is receiving packets from one adapter and sending it over to another. (like eth0 -> eth1).

Interested only in IPv4,

#define NPROT_ETH_TYPE               0x0008 //IPv4

The filter is defined as,

#define NPROTO_PACKET_FILTER  ( NDIS_PACKET_TYPE_NO_LOCAL|    \
                                NDIS_PACKET_TYPE_DIRECTED/*|    \
                                NDIS_PACKET_TYPE_MULTICAST|   \
                                NDIS_PACKET_TYPE_BROADCAST*/)

The receiving side is checking for loopback packets as shown below,

    // Leave the packet if loopback flag is set.
    if( NdisTestNblFlag( pNetBufList, NDIS_NBL_FLAGS_IS_LOOPBACK_PACKET ))
    {
        //
        // Ndisprot is not interested in this NetBufferList, return the
        // NetBufferList back to the miniport if the miniport gave us
        // ownership of it.
        //
        break;
    }

and when I send packets down the road, the SendFlags is set to zero to avoid loopback as per MSDN.

NdisSendNetBufferLists(        
                pOpenContext->BindingHandle,
                pNetBufferList,
                NDIS_DEFAULT_PORT_NUMBER,
                0);

Even after raising all these hurdles, my prottest is receiving loopback packets, as it is evident from wireshark.

Any idea?

Using NDIS6.0, ndisprot60, Dev: Win7, Test VM: Win2008 R2

Answer 1

If you're setting NDIS_PACKET_TYPE_NO_LOCAL and sending the NBLs without the NDIS_SEND_FLAGS_CHECK_FOR_LOOPBACK flag, then NDIS won't deliver loopback packets to you.

Wireshark isn't showing you what your protocol receives. Each protocol can receive a custom set of traffic. So Wireshark is only showing you what Wireshark receives :)