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

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Cannot connect MacBook Pro (Retina, 15-inch, Mid 2015) (10.13.3) to the internet through my Apple USB Ethernet Adapter. I am receiving this error under System Preferences/Network:

  • "Apple USB Ethernet Adapter has a self-assigned IP address and will
    not be able to connect to the Internet."
  • IP Address: 169.254.59.248
  • Subnet Mask: 255.255.0.0

I can connect to the internet with the same ethernet port on my Windows 10 machine. When I replace the IP address with a the Wi-Fi IP address I use to successfully connect to the same network under "Using DHCP with manual address", the Apple USB Ethernet Adapter icon is green and displays the message "Apple USB Ethernet Adapter is currently active and has the IP address xx.xx.xx.252." However there is no actual internet connection (i.e., I cannot visit any website).

According to this solution to a similar problem, I can:

  1. Find and disable whatever firewall is intercepting the DHCP return traffic. According to System Preferences/Security & Privacy/Firewall, my firewall is off. Is there anywhere else I can check for additional firewalls? Would firewalls somehow impact ethernet and Wi-fi differently?
  2. Inspect the network traffic or the router logs to see if and why the Mac DHCP broadcast packet is being ignored. How do I check network traffic on my Mac? I am comfortable using the terminal.

I have also tried steps listed as potential solutions in this post:

  1. To reset the firewall, go to the /Macintosh HD/Library/Preferences/ folder and remove the file called "com.apple.alf.plist," and then restart your computer. On my computer I went to /Library/Preferences/ and ran sudo rm com.apple.alf.plist
  2. If that was already set, try the "Advanced" button, then "Renew DHCP Lease"
  3. Removing their "Ethernet" config from the Network settings and then re-adding

Does anyone have other suggestions? Thanks in advance

Best Answer

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.

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