Thanks for your reply!

According to the "Universal Serial Bus Class Definitions for Communications Devices v1.2":
In Section 6.3, which describes notifications such as NetworkConnection and ConnectionSpeedChange,
there is no mention of duplex status.In particular, for ConnectionSpeedChange, its data payload
only contains two 32-bit unsigned integers, corresponding to the uplink and downlink speeds.

Since CDC has no way to obtain the duplex status of the device, ethtool displays a default
value of "Half". I think it would be better to display "unknown" instead of potentially showing
incorrect information — for example, my device is actually operating at 1Gbps Full-duplex,
but ethtool shows 1Gbps Half-duplex.