Dropping Ethernet Connection on Big Sur

I experience the same problems after upgrading to Bug Sur. I have tested with several ethernet cables. I think the problem is with the driver for the thunderbolt ethernet adapter as it continues to add new ethX devices until reboot when it resets back to default.

I'm now up to en7 after 6 problems

I did not notice that until you mentioned it. I am now up to en9 ! I have been using:

sudo ifconfig en0 down

sudo ifconfig en0 up

in a terminal window to get it to restart the network service. This always works, so you don't have to reboot. Maybe I should just make a chron job that does this a few times per day ...

@KingBowler: agree with your point about Apple Engineering monitoring these posts. Big Sur has been out for 5 months now, and this is still an issue.

Also, like you, I *need* Wifi on for location services, and to enable Apple Watch unlock for the Mac.

Agree that this is an issue with the OS, or driver versions needed to work with the OS. Whatever it is, it needs to be fixed. I think there's no shortage of instructions from users in this thread to enable Apple engineers to recreate the problem.

There may be an additional issue with external ethernet adapters, but many of us are having the problem with the built-in ethernet in Mac Mini's and iMacs, so it is not necessarily anything to do with your external adapter. It seems to me more likely to be a change to the ethernet "core" code in Big Sur vs. all older OS X versions. I am guessing it was somebody's idea to improve security that has this bad side effect.

Thanks you, @diegoicosta, because based on your post, I also decided to buy a different docking station and it solved my connection problems. I went for the CalDigit TS3 Plus Dock and bought it at the Apple Store. Instead of USB-C, it uses a Thunderbolt 3 connection with the MacBook which some on this forum indicated would be one of the keys to resolving the issue. Well, apparently it does because all network tests run at full speed now all of the time, no more drops to 90Mbps. I can sleep and wake my MacBook and on it goes at top-speed (in my case 512Mbps external internet (speedtest) and 1Gbps internal network to NAS. I have tested the speed many different times over the multiple days since I installed the dock and the results are at max. speed and 100% stable and consistent at all times. Yay!

BTW, for business travels I also bought the portable version CalDigit Thunderbolt 3 Mini Dock. Did less testing but it uses the same Thunderbolt technology and all the tests I did run with it were the same as with the TS3 Plus: exact same speed and stability. Great product.

For those of you who want to buy the dock also, let me share my experience with the monitor. It is immediately recognised and runs plug & play (no additional software required) - but if your monitor is connected with HDMI instead of DisplayPort, make sure you have an ACTIVE DP-to-HDMI adapter or cable. I had an old passive DP-to-HDMI cable at hand so I tried it first but that didn’t work, you really do need the active version. I got the CalDigit one (link) and it solved the problem.

Noticed some updates on this forum today which triggered me to provide a further update on my experiences since I started using the CalDigit TS3 Plus Dock. With now one more week using this Thunderbolt solution. I can confidently say that I have tested all scenarios repeatedly now: Extended very long online hours, Sleep and wake the MacBook, Shutdown and startup or Restart it and the results remain rock solid: stable and consistent top speeds to my NAS and external internet. I also upgraded MacOS Big Sur to 11.3, no issues. Extremely happy and for me the case is closed.

I appreciate that this topic also covers other scenarios (MacBooks with built-in ethernet) and I cannot comment on that but for those who visit this forum with a similar scenario as mine (MacBook Air M1, Big Sur, docking station for Ethernet and other HW connections), the solution is clear now.

Have you ever looked at Console - Crash Reports to see what process crashes? My Macbook Pro runs over Ethernet and Wifi all day long w/o issues.

I've also found that your Wifi source can be problematic too. There have been a couple of time where my Ubiquiti setup was problematic for Macs specifically cause of some obscure setting.

@mr_ggg first time you run it it’s normal for it to throw an error because the last two lines of the install script are in essence a reinitialization (disable then enable). On first run there is nothing to disable.

To properly check if it’s working go to /tmp in terminal, issue the command ‘ls -lat | head’ and towards the top you should see a log file timestamped to the last time the task ran, like below. It will not show in the active launchctl list because it runs on a schedule and finishes execution quite quickly.

-rw-r--r--  1 root   wheel  271 Jun  6 15:41 restart_en0.log

Once it actually does its thing and repairs the ethernet connection it will drop a second log file timestamped to when it detected that the en0 was malfunctioning:

-rw-r--r--  1 root   wheel   10 Jun  6 06:26 restarted_en0.log

I have M1 notebook with Big Sur 11.2.3.

When Mac goes to sleep or shut down, the wired ethernet (via Aukey hub) does not re-connect. Unplugging and replugging the cable does not re-establish connection, If I disconnect the hub (c connector) from the Mac and plug it back, ethernet comes back up.

I will give the terminal kick a go..

usr/bin/sudo ifconfig en0 down

/usr/bin/sudo ifconfig en0 up

Curiously it seems (at least today) it doesn't totally break the network stack forever, but it does take a few seconds to recover. Accessing the NFS share via Finder causes the problem more readily than say straight ls at a shell.

So I ran Wireshark on the server holding the NFS share, which also hosts LDAP, and got the following: lots of spurious retransmissions. Something is getting quite unhappy here.

These start the moment Finder hangs. Given that it involves port 389, looks like in my case this is more related to LDAP rather than NFS, so time to check the Mac's OpenDirectory config. (Either way, shouldn't clog up the entire interface.) However I don't know how much useful information is here -- it could be that these retransmissions are a second-order symptom not immediately related to the root cause.

MY HARDWARE SOLUTION

So I had the issue with a USB ethernet adapter on a MBP (2019, 16"). It's the same disconnect issue that others are having, where I had to unplug/plug back in the USB ethernet adapter after a restart.

After reading through this entire thread (because this issue is REALLY annoying), I solved it by swapping out the ethernet adapter I was using (CableCreations branded, Realtek chipset) with a cheapo AmazonBasics branded one I had lying around (Asix AX88179 chipset). This adapter was NOT plug-and-play; I had to read through the Amazon reviews to find the chipset, and then Google it to find the site for the drivers (https://www.asix.com.tw/en/support), then fight with MacOS to allow me to install it... BUT IT WORKS! No more having to unplug/plug back in the adapter after a restart, and a relatively cheap (free, in my case) solution.

I hope this helps someone.

Have not been here in a long while. I have been using the scrip mentioned a few pages back, and have not had any problems in about 6 months. After so many updates of Big Sur I thought I would uninstall the script to see if anything changed. After two days my ethernet failed again. Interestingly, I also have WiFi on now since I use my Apple watch to unlock this computer. However, even with WiFi on I still could not connect to the web without disabling and reenabling the ethernet. So, I have reinstalled that script. This might be fixed in Monterey, but I had big problems ( unrelated to Ethernet ) after upgrading and had to downgrade back to Big Sur.

FIxed: All I had to do was

sh ./install_en0_watchdog_service.sh

instead of

./install_en0_watchdog_service.sh

No idea why the first line of the script did not do that for me.

After this last update to Big sur 11.3.1 I have started to have this issue on M1 MBP with external ucb-c/ethernet dongle.

Issue seems to temporarily be solved if I remove and re-insert the dongle.

I am seeing the same thing on a 15" 2018 MBP running Big Sur 11.1. I am also seeing this across both wireless and wired connections. I can usually get my wired connection back by unplugging the USB-C -> Ethernet Adapter and plugging it back in. Wireless will require a reboot about 50% of the time. Never had a problem before upgrading to Big Sur.