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

Question

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

Answer 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.

Answer 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.

Answer 3

I troubleshoot this with the tcpdump command.

1. Disconnect the USB device
2. Open System Information / System Report - https://support.apple.com/guide/system-information/get-system-information-syspr35536/mac
3. Select Network on the left
4. Note which devices are there, plug in the USB and refresh.
5. Find the BSD Device Name for the adapter ( it might be en6 for instance )
6. Open terminal app as an admin user (if possible - admin means your account has a check in users and accounts system preference and is not a “standard” account)
7. Type sudo tcpdump -i en6 and press return
8. You have to type your account password (it won’t show on screen)
9. Then when you plug in the Ethernet cable, you should see all the traffic on that adapter.
10. Make sure you set it to DHCP in network settings and you should see it asking for an address and other traffic.

If this is too much information, you can capture the trace to a file and get help from support or a network friend.

• https://developer.apple.com/documentation/network/recording_a_packet_trace

Once you know the DHCP request is being sent you might need ipconfig getpacket en6 to inspect what the DHCP server sent or investigate why the gateway and switch isn’t routing your request to the DHCP server or service.

Answer 4

I had this issue and solutions were impossible to find. There is so much out there about the DHCP service failing and why that might be - that's not the issue here. My setup is that I have a Thunderbolt dock with ethernet (Belkin). 'At some Point' it ended up only handing me a notice of 'Self-Assigned IP'.

The solution, after days and possibly weeks: Restart your computer Go to System Prefs -> network, Delete your thunderbolt service Then Find 'Add Service' Add 'Thunderbolt Ethernet Slot' or whichever fits

• The key is that in my case this was not the same service as before. It is a new entry to the list.

So basically my previous service - which ran for over a year- became useless. The new one works fine. That is as good as it gets for an explanation on my part.

I suggest you try out every service you find on the Add-List until it works :)

Good luck

Answer 5

I had this issue when unplugging my router and trying to hardwire my computer. I called my ISP and found out each time I unplug and go from using a router to not using a router, I had to reboot my modem. I had my Ethernet cable plugged into my computer and modem and once the ISP reboot my modem it said “Connected” and the internet worked. Posting this in case it helps anyone else!