It works with up to 100mbps, and it shows in Network as "USB 10/100LAN", but I know it can do up to 1000mbps, but when trying to add + a new interface, the "USB 10/100/1000 LAN" does not appear as an option. The rest of the dongle works. Ethernet adapter works up to that speed.
How can I make the Mac recognise the full speed of the dongle, namely connect under a "USB 10/100/1000 LAN" connection and actually run full speed?
It says in the box 1000mbps.
I had another adapter, different model, that stopped working, that did show as "USB 10/100/1000 LAN", and did run close to 1000mbps in tests.
It reaches 1000mbps in other laptops and the seller has confirmed other clients, presumably using other laptops or OSs, don't have the problem.
It's a non-branded dongle. I have tried installing Realtek drivers but it didn't solve the problem.
Best Answer
Judging from your screenshots it seems like the LAN cable is not directly plugged into your Mac, instead:
LAN cable→USB 2.0 Hub→4-port USB 2.1 Hub→USB 3.1 MBP ControllerUSB 2 spec does not allow for high speed data connection like 1GBit/s. As mentioned in the system report, the maximum speed is 480MBit/s. Therefore you can't establish a 1000MBit/s connection.
As long as you have one device in this connection tree that is not at least capable of USB 3.0 speeds, you will not get the faster 1GBit/s speed on your LAN connection.
Edit: There is another faster
4-port USB 3.1 Hubbeing mentioned in the system report. I think that since your dongle has so many ports, it also has two different controllers that are being recognized by the Mac and shown as separates Hubs, although they are one dongle.