I’m an EE too. Bachelors and Masters. Also specialized in digital design before moving on to optics and quantum. Your analysis is accurate. Well done.
Thanks for the kind words. As you know, decent quality ethernet board connectors often come with emi/rfi filter chips, tiny bitty things either pre-installed on the connector daughter board, or inserted under it prior to its insertion. Apparantly china found a way to put in tiny microprocessors in there instead. Ruh-roh!
They could be programmed to wait awhile, sniff, report back...almost anything. Since they would be at the hardware layers (layers 1 and 2) of the 7 layer OSI model of ethernet, it would be extremely difficult to detect.
Physical inspection could get them, perhaps, but if they’re carefully disguised, good luck. Maybe a tiny height difference.
But done right, software wouldn’t detect them. Not even at the binary level, including firmware or anything.
Basically, it’s a built in, preprogrammed, “at will” sniffer. It could even add or change incoming packets. Or monitor every ISP the board connects to, save and rebroadcast in timed chunks to another ISP...etc.
It’s a computer in between. Perfect “man in the middle.”
And from what I’ve read, the CIA and NSA have things like that already.