How to revert to original DNS for ethernet on iMac?


macrumors newbie
Original poster
Jan 13, 2020
A while back I changed my DNS to Cloudflare's I entered and in my DNS Servers list (in System preferences > Network > WiFi > Advanced settings > DNS tab), not knowing that would not let me use a wired connection. I have a message saying "Ethernet has a self-assigned IP address and will not be able to connect to the internet". So I'm stuck using a wireless connection, I haven't had any issues with the internet but want to switch back to a wired connection but can't remember my original DNS. How do I find this? I read another thread with the answer to remove all DNS servers and then press "renew DHCP lease" but I don't know if that's safe to do. I can always change it back to the DNS afterwards (edit: I am using DHCP)
Last edited:


macrumors 68000
Jun 30, 2007
"Ethernet has a self-assigned IP address and will not be able to connect to the internet".
The message is telling you that your Mac is unable to get a an IP address from a DHCP server and so creates (assigns) one itself. Since the DHCP server did not supply router and DNS server addresses you don't have any internet connectivity.

Normally the simplest thing to do is set your Ethernet adapter to use DHCP so that it gets its' router, IP address and DNS servers from your internet (cable?) router DHCP server. Get that going first to verify that you can use both WiFi and Ethernet. If you look in Network preferences (for Wifi, Advanced) you will see the assigned IP address if you have also set it there to use DHCP. They should be different.

Screen Shot 2020-01-14 at 2.13.52 AM.png Screen Shot 2020-01-14 at 2.13.35 AM.png

There are a lot of DNS servers available. If you do do not want to use the server suggested by your internet provider than you can choose one yourself. This selection is typically determined by which DNS servers are fastest (resolve addresses) in the shortest period of time. There are programs such as the one below which one can use to determine which DNS servers are the fastest.

Screen Shot 2020-01-14 at 2.35.49 AM.png

Cloudflare, if I understand it, supplies security services. In terms of the best configuration for their services you would need to consult with them.