MacOS – How to use 3rd-party USB Ethernet adapter with El Capitan

The solution is to try and reset as many network related system preferences as possible. To be more specific:

1. Unplug the Thunderbolt Ethernet adapter.
2. Create and Apply a new default network location (system preferences).
3. Remove all older pre-existing network locations.
4. Remove the following preference files (global and user specific found in /Library/Preferences /Library/Preferences/SystemConfiguration and ~/Library/Preferences):

com.apple.network*.plist NetworkInterfaces.plist

5. Restart your Mac.
6. Connect your Thunderbolt Ethernet adapter as well as the network cable.
7. Add a new Location inside the network system preferences (AGAIN!) and remove the one added previously in step (2).
8. Wait a few minutes (close the system preferences).

Here is what I observed while trying to solve my issue:

I always used to have two Thunderbolt related entries in my network settings:

1. Thunderbolt Ethernet
2. Thunderbolt Bridge

I believe the bridge may be added by default and the ethernet version may be added on demand, when you plug in an ethernet adapter.

While my connection was "broken", however, this Thunderbolt Ethernet service / interface never appeared or worked again, so possibly some of the settings files related to it were broken.

After removing all old references (from the old locations) to it as well as the listed preference files, I now get the following three default services listed, when adding a new location into the network preferences:

1. Thunderbolt Ethernet
2. Wi-Fi
3. Thunderbolt Bridge

If you don't get these three and you are using a Thunderbolt Ethernet adapter, you may have the same problem as I had and should follow the advice above.

I NetBoot with those all the time (Thunderbolt mostly). This is an Apple dongle, right? As long as it's connected before you start up then it'll load the driver.

You can NetBoot in verbose mode. Set the Startup Disk in System Preferences then restart while holding Command-V (I usually set it permanently on test systems: sudo nvram boot-args="-v").

Not seeing any entries from that adaptor's MAC Address in the server's system.log means the traffic isn't making it to the server for some reason. You can confirm by getting a server-side packet trace (assuming you're using en0):

sudo tcpdump -i en0 -s 0 -B 524288 -w ~/Desktop/NetBoot.pcap

I usually filter in Wireshark for bootp or tftp to see how far along things get.

You can get a client-side packet trace by using either a "dumb hub" (not as common these days) or mirroring a port on the switch (assuming your network gear can do this).