So I have searched far and wide and have not found a solution. I have tried most of what people have posted here (some over 5 years old) to no avail.
The problem: I use my computer connected via Ethernet all the time and it works fine. Then I will lose internet and I will go to the Network preference and renew the DHCP lease on Ethernet and then it will appear as a Self-Assigned IP with a yellow dot. My wifi never stops working and I can continue to use the internet using wifi. Eventually Ethernet will come back on its own (back to a green dot). I have only managed to get it to come back sooner by rebooting my cable modem. Note that I use an Ethernet cable that has been embedded in my wall to the closet which has my cable modem, router, and switch with other Ethernet cables to the other rooms of the apartment. Here is a list of what I have tried:
- Using a different patch cable from my switch to the female Ethernet cable leading to the room with the iMac.
- Unplugging the Ethernet cable from the back of the iMac, from the patch panel, from the switch, from the router.
- Turning the switch on and off.
- Rebooting my router
- Power cycling the router
- Deleting network preferences in
/Library/Preferences/SystemConfiguration - Deleting the firewall settings
- Deleting the Ethernet option and recreating it
- Rebooting the iMac
I did not try using a different Ethernet cable from the switch to the iMac because ultimately I have no problem getting fast connectivity via that cable, its not like I cannot get Ethernet to work, the issue is it going out and then coming back and having to restart the cable modem (and at times the mac too) to get back on ethernet. I am on an iMac 19,1 running OS X Catalina (10.15.7) with plenty of RAM.
So frustrating that physical connection has these issues. Any idea what could cause this?
1 Answer
Any idea what could cause this?
Fundamentally, it is an intermittent problem with the communications over ethernet between your computer and your router.
In most domestic home networks your router provides the DHCP service by which your computer is assigned an IP-address. If your computer cannot get an answer to it's DHCP request at startup, or after an ipconfig renew, the computer will use a self-assigned IP-address and will then normally not be able to route packets correctly to other networks.
So either your router is unreliable and occasionally unresponsive or you have a cabling problem.
It seems you lose Internet access suddenly at times other than system startup, in my experience this is usually a problem with your ISP connection and router. Some router/ISP combinations have fewer outages or recover more quickly. However it could also be caused by bad cabling, especially any that are accessible or subject to heat cycling, movement, etc.
In your case I would at least try replacing the ethernet cables one by one. Since they are cheap. Before doing so I would look at the Ethernet interface statistics and make a careful note of the numbers of low-level errors that it is seeing over a period of a few hours. You can then do a before and after comparison.
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