Interesting WinDbg Issue


I have a strange issue that I?d like feedback on. I was struggling with getting WinDbg to attach to a system via ethernet to do some driver debugging and for days the host would not attach to the target. I have multiple systems in our lab running Windows 10.1607 and no issues with network debugging on any of them except one system. The system in question has a COMExpress module.

I checked all the obvious things:

Firewall disabled.
Ping works between host and target in both directions.
Disabled all other ethernet network ports (system has 4) except the one I?m targeting.
Specified busparams in the dbgsettings for the bus.device.function of the target adapter.
Verified all params to bcdedit are correct.
Correct version of debugging tools
System up-to-date

After failing to get the connection working, I decided to break out Wireshark and collect traces and compare them to a known-good working system. I installed Wireshark on the host and configured my traces simply collecting everything from the target?s IP address. At this point I thought well I should start up WinDbg and viola, target connects to WinDbg and works like a charm. To make sure I wasn?t imaging things, I killed everything, rebooted and started WinDbg and no connection. I went back and forth with this half a dozen times having Wireshark running then not. The target reliably connects to WinDbg when Wireshark is running, but won?t connect without Wireshark running.

Now I?m fairly ignorant about networking, but it would be good to have better understanding of what I?m seeing here. Any thoughts on this would be greatly appreciated.