iMac27 Dropping Ethernet Connection

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I am stumped. For the past 2 days, my iMac27 comes up with a dropped ethernet connection after being turned off or sleeping. Other computers are working just fine on the network, but the iMac has no internet. Running the Network Troubleshooter shows that the cable is disconnected. Changing the cable helped yesterday but not this AM. I have reset permissions and verified disk with Onyx to no avail. I have wiggled cable in iMac port to no avail. Only recent software install was update on Java. Could this be problem?

How to begin to solve this? All ideas would be welcomed.
 

chscag

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Are you running Yosemite on the iMac? Lots of connection problems being reported by iMac users who have Yosemite installed, however, most of those connection problems involve WiFi. Supposedly fixed by 10.10.2 but reports are that many problems still exist.
 
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Dropping Ethernet connection

I solved this problem and several others by performing a clean install of Yosemite OSX 10.10.2 . I don't understand why this helped but it did. I took the old HDD, placed it in a OWC firewire box to use as a archive volume, and installed new SSD with HDD to do this.

This may be helpful to some others.
 
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Good work.

Have posted here many, many times this continuing upgrade of operating systems must have a downside somewhere. Always make a bootable thumb drive of each system and do a format and clean install. For nnstance a 2010 11.3 iMac was released with Snow Leopard OS X.6, and if one were to do each upgrade since, would have been through Lion OS X.7, Mountain Lion OS X.8, Mavericks OS X.9 and now Yosemite OS x.10.
 
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I am having the same ethernet not connected issues on my iMac computer:
iMac (Retina 5K, 27-inch, 2017
macOS Big Sur v 11.2.3

Will find no internet connection occasionally in the morning and sometimes late in the evening after not using for a few hours. Router/WiFi on other systems (iphone, iPad, TV (direct ethernet connection), etc) work fine.

Have to reboot or restart to reconnect the iMac to router via ethernet cable.

Help please. FYI...rely on iMac automatic configuration so not good a troubleshooting.

Thank you in advance.
 

chscag

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The first thing to do is substitute another ethernet cable, a known good one or a new one. Ethernet cables use a RJ 45 type connector which are very susceptible to failing. I have had to replace these types of cables numerous times over the years in the work that I formerly did.

Also try switching to a different port on your router.
 
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Will find no internet connection occasionally in the morning and sometimes late in the evening after not using for a few hours. Router/WiFi on other systems (iphone, iPad, TV (direct ethernet connection), etc) work fine.

Have to reboot or restart to reconnect the iMac to router via ethernet cable.


I think I would be suspecting the internet cable, the cable ends or ethernet receptacle connector on the router or Mac ends.

Have you got another ethernet cable you could try using???


- Patrick
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If after checking/replacing the ethernet cable you still have issues, something else you can try is creating a new ethernet network connection. Here is how you do that:

1. Go to System Preferences -> Network -> Make sure your current Ethernet connection on the left is selected. At the top there is a box labeled Locations: Automatic - click on Automatic and select Edit Location.

2. In the box that open look at the lower left corner for the " + " box and click on it. You are going to create a new location.

3. Give your new location a name - something like Home or what ever you want to call it. Make sure your new location is selected and click done.

4. When the box closes and you are back in the Network box click apply. * It will indicated the ethernet connection is disconnected at first and this is normal as it rebuilds the network connection. (And here I am assuming you have Configure IPv4 set to Using DHCP.)

If you need picture take a look at this article: https://www.support.com/how-to/how-to-fix-wired-or-wifi-connection-on-mac-12831

Lisa
 
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If after checking/replacing the ethernet cable you still have issues, something else you can try is creating a new ethernet network connection. Here is how you do that:

A very good suggestion for them to try Lisa.

Thanks for adding it.


- Patrick
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Thank you for the suggestions. And it happened again. Woke up this morning and no internet connection. I will provide more detail below.
Friend who has his own IT business set up my home system with 3 Netegear Access Points. AP 1 is connected to my iMac with ethernet cable. APs 2 and 3 are located in bedrooms to on either side of my large home to provide good wifi access throughout and outside in patio. They all work perfectly with exception of iMac dropping connection.
Situation this morning.
1. Netgear AP port #3 status light green. So the AP is working shows "connected" to my iMac.
2. System Preferences>Network>: Shows Ethernet 2 as “ yellow” and Status: "Connected. Ethernet 2 using self-assigned IP address and will not be able to connect to the internet"
3. System Preferences>Network>Advanced drop down page: Shows different IPv4 Address and different Subnet Mask, and no Router number.

So for some reason when my iMac goes to sleep after not being used for a few hours it disconnects.
 
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So for some reason when my iMac goes to sleep after not being used for a few hours it disconnects.
No, that is not what the reports are saying. What seems to be happening is that although your iMac is connected to the Netgear, it is not getting an IP assigned/renewed by the DHCP server and therefore cannot connect through Netgear to your ISP Modem and then to the internet.

In System Preferences/Network/Ethernet is the "Configure IPv4" set to "Using DHCP?" And on the Advanced page, is TCI/IP/Configure IPv4 also "Using DHCP?"
 
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System Preferences>Network/ "Configure IPv4: Using DHCP"
System Preferences>Network/ Advanced "Configure IPv4: Using DHCP"

Again, the IPv4 Addresses are different as are the Subnet Mask numbers/addresses. Plus, "no" Router identifier is shown where as when connected, router number is shown.
 
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Also, I "do not" put my computer to sleep. Only the screen saver starts after 1 hour.
 
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System Preferences>Network/ "Configure IPv4: Using DHCP"
System Preferences>Network/ Advanced "Configure IPv4: Using DHCP"

Again, the IPv4 Addresses are different as are the Subnet Mask numbers/addresses. Plus, "no" Router identifier is shown where as when connected, router number is shown.
Yes, the IP numbers will be different. Your router should be issuing a number like 192.168.x.y or 10.x.y.z. But the default internal number start with 169.x.x.x or 127.x.x.x, usually. The system needs some number just to run, so it uses a pre-defined dummy as the feedback number. When it connects to the router, that number is replaced by what the DHCP server in the router assigns, which are in one of the two ranges I gave. Then the router maps the specific number from your machine on the internal network to the IP address assigned to the router from your ISP so that it can then translate incoming and outgoing packets for you. So, again, what seems to be happening is that for some reason the IP is not being renewed and the iMac defaults to the loopback IPs instead of the IP needed to communicate with the router. Given that other devices are renewing, it is some setting in you iMac Network setup.

Did you try what Lisa suggested about a new location? You didn't say whether or not you had done that.

For reference, here are my settings both in System Preferences/Network and in the Advanced tab.
Screen Shot 2021-03-20 at 10.51.50 AM.png

Screen Shot 2021-03-20 at 10.53.39 AM.png
 
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I shutdown and switched iMac ethernet cable connection from port 3 to port 2 on my Netgear Access Point device. Restarted and works fine. Will see how that works.

And my System Preferences>Network/ settings in network and advanced are like yours, only in the network settings, the DNS Server number "192.168.0.1" is visible, but greyed out and not dark black.
 
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And my System Preferences>Network/ settings in network and advanced are like yours, only in the network settings, the DNS Server number "192.168.0.1" is visible, but greyed out and not dark black.
You can change the DNS in the Advanced tab, under DNS. Your setting points to your router, which then gets a setting from your ISP. In my settings I have two Google DNS servers and a CloudFlare server set, then if they fail (they are very reliable) it goes to the router. I find the Google and CloudFlare to be much faster than the default router.
 
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I occasionally have a device that just won't "phone home" to get an IP address. In that case I manually assign one on the stubborn device. To manually set your network settings in the iMac - in advanced under tcp/ip change Using DHCP to manual and input the settings for your network.

Example: IP address: 192.168.0. 50. ( assuming your network has "0" in the third spot.)
Subnet Mask: 255.255.255.0
Router: 192.168.0.1 ( this is only an example as I have no idea what the ip address is of
your local router.)

Look at the settings under System Preferences -> Network -> Advanced -> TCP/IP on a connected Mac will give you all the above information. You can put that in manually on the one having issues if it is not connected BUT be sure to change the IP address!

All you need to do is use the first three sections (192.168.0.xxx )and change the forth one to what ever you like or if it has an IP address make it the manual one so it can not change.

I hope I am explaining this clearly.
 
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If you do what Lisa suggested, make sure you set up DHCP in the router so that it doesn't assign the number you manually entered to any device. If there are two with the same number, the two will conflict and you will see errors on both. Most, if not all, routers allow you to set aside numbers it won't assign.
 
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Switched ethernet connection port on my Netgear AP device from #3 to #2 yesterday. Worked fine this morning and no issues thus far. Fingers crossed. Appreciate all of the support and guidance from this group.
 
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Switched ethernet connection port on my Netgear AP device from #3 to #2 yesterday. Worked fine this morning and no issues thus far. Fingers crossed. Appreciate all of the support and guidance from this group.


As the old saying goes, a good safe port is the best place to be in any storm. ;)

Good quick fixing on your part and let's hope it stays that way.

- Patrick
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