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IP ECN bits reset? RRS feed

  • Question

  • (Apology in advance, I don't know where to exactly post this, and so I've posted this same question in 2 other forums too -- WFP, WSK)

    I'm verifying IP ECN bits usage with UDP packets.

    I have a test Winsock application that crafts a UDP packet via "raw" socket, sets the ECN bits, and sends it over the network. But Wireshark reports that the outbound packet's IP ECN bits are zero, not the specified setting. I've tested the above in Windows 7 Ultimate SP1 x86.

    Strangely, when I ran the same test app under Windows 8, everything's OK. Also, when I used the freely available packet generators like Colasoft instead of my test app, there's no problem too (Windows 7/8).

    Experimenting further, I moved the logic for setting the ECN bits from my test app to the kernel mode using WFP filtering at layer FWPM_LAYER_OUTBOUND_IPPACKET_V4. Same result - driver's ECN modification for the outbound UDP packet doesn't persist in Windows 7.

    How can I set IP ECN bits of a UDP packet sent from Windows 7?

    Am I missing something in my Winsock application, and/or WFP driver? Or are there some configureable settings  within Windows 7 related to ECN that I could toggle on/off?

    Thanks.

    Wednesday, May 8, 2013 2:56 AM