Recently I purchased a USB Type C to Ethernet adapter cheaply off the internet and I was wondering if it really supported gigabit connections. It was advertised as a 10/100/1000 USB adapter and I was interested in checking if it indeed was capable of achieving such speeds. My new 2018 MacBook Pro, like most new laptops, doesn’t come with a built in ethernet port.
Initially I checked the system report. This can be accessed by clicking the top left Apple Logo > About this Mac > System Report.
However, it gives the following sparse details: 
While it does claim to have a 5Gb/s bandwidth, and by extension support for a gigabit connection, I’m not so sure I can believe it.
Determining the supported link speed
The answer lies in the built application Network Utility.app. You can find that in your Application folder or by using the Spotlight Search.
This Network Utility will display the maximum link speed that is supported by your Ethernet dongle.
Note that you can also verify if your dongle supports gigabit connections by using the free online tool Speedtest.net. Any download speed above 100Mb/s would be indicative of a chipset capable of a gigabit connection.
If you are interested, you can find my main blog here.