2021 16" Mackbook Pro Ethernet and Wifi not working at the same time

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Level 1

13 points

2021 16" Mackbook Pro Ethernet and Wifi not working at the same time

I am experiencing and interesting problem with the new 2021 16" Macbook Pro and Belkin USB-C to Ethernet Adapter offered by Apple. I am unable to use Ethernet and Wifi at the same time. Either will work alone. When I am connected to the network with WiFI, as soon as I plug in the Belkin Ethernet Adapter all networking stops. Similarly, if the Belkin Ethernet Adapter is connected and working and I turn on WiFi, as soon as it connects, all the network stops. If I unplug the Adapter or turn off WiFi, networking resumes. I've observed that the router will drop the Belkin Ethernet Adapter whenever I attempt to connect both at that same.

The behavior is the same regardless of which of the Macbook's USB-C ports I use. I've also tried Ethernet adapters from other manufacturers and the behavior is also consistent.

Another curious behavior, is none of the Ethernet Adapter I tested are able to pick up an IP address via DHCP. They will work if configured manually.

Currently, I have Ethernet and Wifi working at the same time on an iMac and an older MacBook Pro with no problems. DHCP has always worked. All are configured to have Ethernet as the default service in the Systems Preferences Networking pane.

Has anyone else experienced as similar networking problem?

MacBook Pro 16″, macOS 12.0

Posted on Dec 8, 2021 6:16 PM

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Answer 1

Best reply

Grant Bennet-Alder

Level 10

127,393 points

Dec 8, 2021 7:42 PM in response to toxop

If networking stops when you add or remove an adapter, that suggests you have something interfering with it. The suspect list included Proxies, either intentional or un-intentional, VPN software, anti-Virus software, and some cleaner and Optimizer software.

The "litmus test"is to restart in Safe Mode.

"Works in Safe Mode, fails in regular mode" generally implies "It's something you added"

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Answer 2

Dec 8, 2021 7:38 PM in response to toxop

Packets going toward the Internet are sent to the TOPMost, Working interface shown in

System preferences > network

Since Ethernet is generally faster, the preferred setup is to use Set Service Order (off the gear drop-down) to place Ethernet TopMost. Then if Ethernet is working, it will be used for Internet-bound data transfer.

Generally, your wi-fi connection will remain active, but no Internet-bound traffic will be sent over it. it can still provide Location data if active.

Your Mac CAN support load-sharing over two similar interfaces (such as the two Ethernet ports in a Mac Pro desktop), but ONLY to "managed" devices (Switches or Routers) that can support Link Aggregation Control Protocol (LACP). Otherwise, Internet data will just use the TopMost, Working link.

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Answer 3

toxop Author

Level 1

13 points

Dec 9, 2021 9:05 AM in response to Grant Bennet-Alder

Safe mode helped. It appears the problem is caused by by Intego's Netbarrier. When its not running I am able to use both Ethernet and Wifi at the same time. I will pursue this problem with Intego.

Thanks very much.

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Answer 4

Dec 9, 2021 9:53 AM in response to toxop

Consider not running intego at all.

Effective defenses against malware and ot… - Apple Community

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2021 16" Mackbook Pro Ethernet and Wifi not working at the same time

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