Apple USB Ethernet Adapter has a self-assigned IP address and will not be able to connect to the Internet

Solution 1:

Assuming that there is no firewall running (you can do this by issuing the command sudo pfctl -d at the command line), there are two possibilities that would be causing this:

• A faulty Apple USB Ethernet Adapter
• Network security measures preventing you from obtaining network access

Faulty USB Adapter

This is fairly easy to diagnose; try another one. If another adapter gives you the same results, it's highly likely the issue isn't the adapter. Additionally, to be 100% certain, take the suspect adapter to a different network (or just connect it directly to another computer). If it works there, the adapter isn't faulty.

Network Security Measures

Getting a self assigned IP address means you didn't get a DHCP offer (and accept it). Manually assigning a known good IP and still not being able to browse means your computer is blocked from accessing the network. This could be due to many factors:

• The port is disabled on a switch. This is done to eliminate the possibility of a rogue actor gaining access to the network by simply plugging in a device. This is not the case here as your Win10 machine works when plugged into it

• The switch could be using Mac Address filtering. The Ethernet adapters (the USB adapter and one in your Win10 machine) have unique MAC Addresses (Media Access Control, not "Macintosh") and the switch could be configured to only allow certain MACs access. This is easy to test/bypass by spoofing the USB Adapter's MAC with the Win10 machine's MAC. If it works, you've got your answer.

• The company (I suspect this because this is very uncommon in home networks) has employed some sort of authentication mechanism like RADIUS that will prevent you from gaining access on an unknown/un-trusted device. Spoofing a MAC address will not bypass this and you'll need to contact your IT admin for assistance.

Solution 2:

I had this issue after switching the Ethernet cable from my Windows computer to my Mac. Apparently the router (which has no Wireless capability) was running as a modem only, and not as a router. When this is the case it only issues an IP address to the first device that connects. Resetting the router and connecting to the Mac first solved the issue.