[stragies]

Was the network port bridged to both PCs all the time (as the description makes it sound, or did only the "active" PC get a functioning network connection? Could you tell from the FDB of the upstream device, if there were more than two MAC addresses active on the port? Did you (hopefully) open it up and make PCB pictures before chucking it?

[simoncion]

This picture from the list of product pictures [0] indicates that the thing acts as an Ethernet bridge. It probably exposes itself as a USB-C gigabit Ethernet device to the machine it's plugged into.

Page four of TFM [1] supports this theory.

Also, this functionality is called out in the product listing and in the manual. I'm over here laughing my ass off because OP got so frightened by this clearly-documented feature that they immediately threw the thing in the trash, rather than first investigating to see if the source of the network traffic was the machines plugged into the device.

[0] <https://m.media-amazon.com/images/I/71GglDmzCYL._SL1500_.jpg> (If this direct link fails, it's the image that has the header "A Stable Gigabit Ethernet Port".

[1] <https://avaccess.com/wp-content/uploads/2024/01/UM-_-iDock-C...> (This is the "DOWNLOAD USER MANUAL" link in the Downloads subsection of the More Information section of [2])

[2] <https://www.avaccess.com/products/idock-c20-kvm-switch-docki...>

[jlward4th]

I'm not an expert on this, but know enough to know the KVM doesn't need its own IP. In fact, the KVM I replaced it with provides ethernet to both my machines (at the same time) without getting its own IP.

[stragies]

The manual, as OP said, does not offer any explanation, why the device might show up with an additional MAC/IP at the upstream switch port, and which services it might offer. OP sounds knowledgeable enough to be able to exclude the possibility, that the additional MAC/IP could be from one of the PCs, like e.g. when playing with VMs using an internal bridge in the Hypervisor.

Maybe the device has a bigger "cousin" device, that includes "control via APP", and this feature was not properly/fully disabled on this one.

[jlward4th]

The network was active for both machines connected to it. And it had its own IP. So 3 MAC addresses in total. I didn't ever open it up. But maybe someone will be interested in buying one and exploring more.