Dropping Ethernet Connection on Big Sur

ttaylor2258, in the mean time you can use my method to get the network back without rebooting. Open a terminal window, and type:

sudo ifconfig en0 down

You will be prompted to enter your password. Then, hit the up arrow to bring that command back up, and use backspace to change "down" to "up" :

sudo ifconfig en0 up

This turns your ethernet off and then on again, to reset it.

This works for me 100%, I have done it dozens of times. I have not rebooted in weeks. I just leave the terminal window up on my desktop so I can easily do this again when needed.

Also, since you have a new computer, you should call Apple as you should have one year of AppleCare. Just putting something here does not necessarily get their attention, it seems to me this is just for users trying to help each other out. In the past I had a problem with a video card on a used MacBook Pro. That thread had over 500k posts over a few years ! I gave up and sold it. Shortly after that, Apple finally offered a fix. I'm sure they won't be a able to fix this, and they will tell you to do some moronic stuff like reboot, and maybe re-install the OS. But, if more and more people report this it should eventually get their attention. You should also refer them to this thread. On the other hand, if they do have a fix, please post it here.

@mr_ggg sorry for the late reply.

Your ~/bin/restart_en0.sh script (found under home directory, bin subdir) should look like the script 1 below. The script has a few chained conditionals and works like this:

• get the IP address of the gateway by checking the route to the Google DNS server 8.8.8.8
• send a ping to the gateway via en0, and
  • if it succeeds (&&), put the message "en0 alive" into standard output
  • if it fails (||) then start a subshell
    • take down en0
    • ___if successful, bring up en0
    • ______if successful, put the message "restarted" into restarted_en0.log
• redirect all standard output to restart_en0.log

There are two things that may have gone wrong:

1. For some reason your ifconfig command isn't reachable at its standard location /sbin/ifconfig. Please confirm that you can run this command and it's not complaining about 'no such file or directory'
2. For some reason the long lines in the script (version1) got somehow truncated or broken in the wrong place during your copy-paste. The install script works well on my machine but may be stumbling on yours. You may want to paste version 2 below into your ~/bin/restart_en0.sh:

Script version1 with long lines

#!/bin/bash
(
gw=`/sbin/route -n get 8.8.4.4 | /usr/bin/grep gateway | /usr/bin/awk '{print $2}'`
/sbin/ping -c 1 -t 5 -b en0 $gw && /bin/echo en0 alive || ( /sbin/ifconfig en0 down && /sbin/ifconfig en0 up && echo restarted > /tmp/restarted_en0.log )
) &> /tmp/restart_en0.log

Script version 2 with escaped short lines

#!/bin/bash
(
gw=`/sbin/route -n get 8.8.4.4 \
  | /usr/bin/grep gateway \
  | /usr/bin/awk '{print $2}'`
/sbin/ping -c 1 -t 5 -b en0 $gw \
  && /bin/echo en0 alive \
  || ( /sbin/ifconfig en0 down \
      && /sbin/ifconfig en0 up \
         && echo restarted > /tmp/restarted_en0.log 
     )
) &> /tmp/restart_en0.log

I got tired of my issue, and really required an ethernet connection with my laptop. So, after reading some advice, I got myself a Belkin USB C-hub, 6-in-1multiport bla bla model AVC008. Used it for a day, without Wifi enabled, and had no more issues at all.

The other (cheaper) device has a Realtek chip, which kept dropping the ethernet port (only the ethernet port, not the rest of the USB ports) after several minutes. It could only be restored on reconnecting the device.

Matt, same here since months. We exchanged every network component without success. It is definitely not your network hardware. It is solely a Big Sur problem. Otherwise it wouldn't even occur on machines with only Big Sur installed out of the box. All machines still running Catalina run without ANY network problem. Apple has just killed the Ethernet drivers and they seem to be unable (unwilling?) to correct this very annoying error in their software. We are running a company network and urgently needed two new machines. We bought the new M1 24" iMacs and none of them work with correct network settings. Only if you enable jumbo frames in the ethernet hardware settings they seem to work but not stable which is no surprise in a network based on the normal 1500 frame size.

Steffel wrote:

I found a workaround on one of or 27" iMac from 2017 running on Big Sur:

Ethernet works when I set the MTU in the Hardware settings of Ethernet to a value larger than 1500 manually. For example an MTU of 1501 works and I get an obviously stable network connection with the built in Ethernet port.

Curious... I tried this in 11.5.2 (both 1501 and 9000), but browsing NFSv4 in Finder is still able to hang the network stack for a minute or more. I'm beginning to wonder whether or not we're all seeing the same bug with different symptoms, or a cluster of different issues.

drmhv, yes this seems to be a different bug you are facing.

I tried this MTU1501 thing on the two new M1 iMacs and on one M1 Mini and all worked immediately with their built-in ethernet ports. I am not sure this really is a workaround yet, because it must proof to be stable for a longer time and in fact this is still a wrong setup as the MTU is 1500 in the network, not 1501.

However, it seems the MTU setting has something to do with the problem because there is NO connection at all with MTU1500 and FULL connection with MTU set to 1501 on 4 different machines, one Intel and three M1.

If you are still interested in trying to improve this problem I suggest you to make

a new network configuration, named for example "Ethernet only" where the only

interface active will be "Ethernet".

If you try it, please report your positive or negative result, this will be helpful for many users.

OK, it's been 9 days now and no issues. I have never, since installing Big Sur, been able to last more than 5 days without the ethernet dropping. So, maybe a clean install , or Monterey upgrade, but in my case both definitely works.

Had the same experience so I switched to a Thunderbolt connected hub and problem was solved. Apple Store has them (CalDigit) at great price.

I have the same problem since upgrading to Big Sur. iMac 21.5" Late 2015 using the driver AppleBCM5701Ethernet.kext. Wifi keeps going but the built-in Ethernet port dies sometimes within hours sometimes within days. To recover I have to go into network properties, deactivate the ethernet card, then reactivate it. It's getting old fast. And MacOS was installed from scratch on a new SSD so any issues with the upgrade from Catalina are out of the question.

I have same exact issue on BRAND NEW MAC MINI M1. I have same issue with MBP 2019 as well. Everything was fine with laptop until big sur and thought maybe I could get a BRAND NEW COMP and not have issue....GUESS WHAT...SAME THING!!! Only thing that has at least kept me somewhat connected has been disabling "wake for network access", but no guarantee, and it has still done it on both machines.

Yao Bin above said they could get the ethernet to work again by opening their router page, but I wanted to mention that does not work for me. I still have to use "sudo ifconfig en0 down", followed by "sudo ifconfig en0 up", in a terminal window. Also, the original thread does not concern the use of external ethernet devices, I wish someone would start a new thread about that. I don't want to give Apple the impression that any of the things mentioned that may solve external ethernet problems apply to me or the original poster. Our problem concerns internal Ethernet, for example my 2018 Mac Mini.

We did't try Wireshark yet but that's a good idea! We will try that next.

The CISCO switches have quite a good network analyzing software included. However it could not find any problem and the logs don't explain what happens. We assume it is the router that gets confused by an error in the Big Sur ethernet driver's protocol. Probably it is a very trivial error in the driver and this doesn't surprise me because they had to re-write it completely.

What I didn't mention is, that older Intel Macs with Big Sur installed showed exactly the same behavior. After downgrading them to Catalina they worked normal again. Unfortunately you can't downgrade new Macs to Catalina...

We are trying to solve this matter since many months now. But it looks like only Apple will be able to correct this by de-bugging their ethernet drivers.

Regards

Stephan

Unfortunately today, day 5, the network failed again. It came back as soon as I typed this in a terminal window:

sudo ifconfig en0 down

sudo ifconfig en0 up

so, problem NOT SOLVED by resetting SMC

@hthompson94 thank you for your return.

Could you run the following command within a Terminal:

ifconfig -a

and paste the result in your reply.