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I am running macOS Catalina 10.15.3 with a USB-C hub from Minix, which has an ethernet port. Inside is an AX88179 chip for which I installed the correct driver. When I start my MacBook or when I plug in my USB-C hub everything works fine. The interface is called 'AX88179 USB 3.0 to Gigabit Ethernet 2'

However, after a few minutes the connection stops working. In the network overview it shows the green dot with 'connected'. When I use the 'Renew DHCP Lease' option the dot becomes orange with the 'Self-assigned IP' message. I see a wrong subnet mask and get an IP that is not within the network (169.254.44.151). The cable is running straight to my modem/switch. WiFi is working just fine all the time.

What I tried:

  • check if my Firewall is off, it is
  • deleted the com.apple.alf.plist file
  • removing and re-adding the ethernet interface in the network pane. This does not work at all.
  • Running sudo tcpdump -i en9 port 67 or port 68 (running sudo ifconfig tells me it is en9) and then renewing the DHCP lease. I get the following line a few times: [time] IP 0.0.0.0.bootpc > broadcasthost.bootps: BOOTP/DHCP, Request from [MAC address I suppose] (oui Unknown), length 300 and am still stuck with the 'Self-assigned IP'.

How can I fix the issue of the dropping ethernet connection and/or the self assigned IP?

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The fact that WiFi is working fine, tells you that the issue isn’t related to your OS. Especially, your firewall can’t be an issue because a firewall won’t allow DHCP traffic then suddenly block it while simultaneously continuing to allow it for another interface. The tcpdump is telling you that the DHCP client that requests the IP from the server is working fine. The “oui unknown” means that the Organizational Unique Identifier (first 3 octets of the MAC address) can’t be found. Which means it can’t identify the chipset.

That leads us to....

This chip, made by ASIX Corp is an off brand, low cost chip used in many discount peripherals also made by off brand and discount manufacturers. In fact, a number of products based on this chip like this Plugable USB to Ethernet not only doesn’t list macOS as supported, it actually says not compatible with Catalina.

The problem then is the adapter and not your Mac. Steer clear of off-brand products and look for adapters that use quality chipsets like Anker USB Ethernet Adapters (I personally use this brand due to their reliability and warranty; 18 months). Generically speaking, look for chipsets from known, market leaders like Intel, Broadcom, Qualcom, Texas Instruments, etc. Chances are, the WiFi adapter used by Apple for its AirPort adapter is a Broadcom.

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