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Microsoft KM-TEST Loopback adapter - how it works? RRS feed

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    Hi, Community and Microsoft network experts.



    I have a question related to principle of work of Microsoft KM-TEST Loopback adapter. As I know, it should work as follow:

    Any network packets which are sent from this interface - are returned by the adapter to itself.


    Is it correct? Why I'm asking: in Windows 2003/XP this adapter worked exactly in this way. I was able to send a network packet from this interface and capture it back. In modern Microsoft OSes (10/2016/2019) this behavior isn't reproduced - when I send a packet from this interface, sniffers (message analyzer/wireshark) register only one event: one egress packet and no returning packet.

    I tried to change Weak host send/receive on this adapter but it doesn't impact on behavior, anyway - there is no returning packet on this interface.

    Could you, please, clarify, how Microsoft KM-TEST Loopback adapter is working today?

    Thank you in advance.




    • Edited by ns.88.ns Saturday, November 30, 2019 10:32 PM
    Saturday, November 30, 2019 9:58 PM

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    Hello ns.88.ns,

    A quick look at the driver shows that it has very limited functionality - it accepts outbound traffic and discards it. It does not loop back the traffic and is not capable of indicating any (even fictitious) inbound traffic. The sniffers are correctly capturing the traffic through this miniport (i.e. only outbound traffic).

    Gary

    • Marked as answer by ns.88.ns Thursday, December 5, 2019 7:13 PM
    Wednesday, December 4, 2019 9:24 AM

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    So, nobody knows?
    Sunday, December 1, 2019 8:58 PM
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    Hi,

    Based on my research, the following is how Microsoft KM-TEST Loopback adapter works:

    The loopback adapter is quite a useful tool that was designed for testing out the network configurations.

    About more details, you can refer the following article:

    How to Enable Loopback Adapter in Windows 10

    Please Note: Since the web site is not hosted by Microsoft, the link may change without notice. Microsoft does not guarantee the accuracy of this information.

    Hope this can help you, if you have anything unclear, please let me know.

    Have a nice day!

    Ellen



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    Tuesday, December 3, 2019 5:55 AM
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    Hi, Ellen.

    Thank you for the reply. Unfortunately I know that the Microsoft KM-TEST Loopback adapter is

    The loopback adapter is quite a useful tool that was designed for testing out the network configurations.

    Yes, I know well what is the Microsoft KM-TEST Loopback adapter and I know how to enable it. My questiion was quite different:  how it is working now, isn't it? You can read it in my initial post. It seems, you read my post not attentive enough. NBD.

    Unfortunately I can't mark your reply as answer - you just pointed to well known information which is fully useless. It's a pity. Sorry for that.

    Best regards.

    Tuesday, December 3, 2019 9:32 PM
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    Hi,

    Let's look forward some ideas from other forum users.

    Or you could open a support request for deep study.

    https://support.microsoft.com/en-gb/hub/4343728/support-for-business

    Thanks for your understanding and cooperating.

    Have a nice day

    Ellen



    Please remember to mark the replies as answers if they help and unmark them if they provide no help.

    If you have feedback for TechNet Subscriber Support, contact tnmff@microsoft.com.







    Wednesday, December 4, 2019 1:56 AM
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    Hello ns.88.ns,

    A quick look at the driver shows that it has very limited functionality - it accepts outbound traffic and discards it. It does not loop back the traffic and is not capable of indicating any (even fictitious) inbound traffic. The sniffers are correctly capturing the traffic through this miniport (i.e. only outbound traffic).

    Gary

    • Marked as answer by ns.88.ns Thursday, December 5, 2019 7:13 PM
    Wednesday, December 4, 2019 9:24 AM
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    Thank you, Gary.

    You confirmed my guessing and tests. So, Microsoft changed functionality of the adapter since XP/2003.


    • Edited by ns.88.ns Friday, December 6, 2019 9:05 AM
    Thursday, December 5, 2019 7:15 PM
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    Hey Gary,

    Is there no knob that maybe turns on the previous behaviour of mirroring the packets received on the interface?

    And ns.88.ns, maybe you can rip the driver that has your preferred behaviour from XP/2003. If the driver is really simple, maybe you can use it on Windows 10 :)

    Saturday, May 30, 2020 5:52 AM