I didn't noticed until today but reading this thread https://forum.pjrc.com/threads/44403...+serial+device I had a look to my network settings...

I found 300+ devices in the list ! Removing them one by one with the Network Preference Panel will take me hours !

So I wonder :
1) the cause ?
2) how to remove them the command line (I could write a bash script)
- with networksetup -listallnetworkservices I can get all the declared devices, so I tried
- networksetup -removenetworkservice "Teensy MIDI/Audio 32" with I get an error "You cannot remove Teensy MIDI/Audio 32 because there aren't any other network services on Teensy MIDI/Audio. ** Error: The parameters were not valid."

Further notice :
- on /dev/ I've only one /dev/cu.usbmodem3955991
- I don't understand how tycmd found a board labeled 3955990
- these two numbers have not changed since I plugged the Teensy for the first time, one month ago

Mac OS Sierra 10.12.6
Teensy 3.6

I really like Mac OS but sometimes... PFEEW !