For desktops I install a new card and for laptops I go get the USB to Ethernet adapter.
Your post is rather long so I can't guess if you left the WiFi on while using the Ethernet or hard assigned the IP anywhere.
Pretty stumped on this one.
Router: TP-Link Archer C9 (default)/ Netgear (test purposes)/ Airport Extreme (replacement)
Mac Mini: 2014
PC: Old Gateway I don't use much running Windows 7.
I came home to find the internet was down due to the Internet light on the router being orange instead of blue. I rebooted it and the problem persisted so I rebooted it and the cable modem but still no connections. I dug into the routers settings to find under "Internet" all the IP address were blank but the DNS settings would show IP address.
I was able to connect via Wi-Fi and came back to examine the issue further and discovered that under the choices for MAC address that if I cloned my Mac Minis IP I could get online via ethernet.
I only mention my PC because while working on the issue I noticed it was on and that it had blue screened and was doing a dump. I must of left it on the previous night while it was running it's virus update and didn't set it to turn itself off.
So today's my day off and I discovered that none of my devices (Apple TV, Tivo Roamio etc) that connect via ethernet will do so with the exception of my PC. They all claim there is a ethernet plugged in but when I force a connection they claim theres no cable or it just can't connect.
I've restore factory settings on the Archer C9 router but the problem persists. I called my ISP and I'm getting a signal. I can plug the cable modem right into the Mac Mini and I'm good to go.
I then set up my old Netgear router and I'm getting the same results when I run the ethernet cable out of it. The same 'Internet' address read as blanks while the DNS shows actual IP numbers. I was able to play with the MAC address options just like the on the TP-Link and got the same options expect it pulled up a MAC address in the custom field which worked. The Archer wouldn't accept any custom ones I entered. That seemed good expect that the old modem was replaced because it would stop working which is what happened shortly after finding this short term fix.
I went back into the Archer C9 and started looking more into the ISPV6 settings to see if maybe that was part of the problem but I must of changed something I wasn't aware of because it as I reset it back it kicked me out and I can't get back in.
So after googling that and coming up with no way into it I made a run to Best Buy and picked up an Airport Extreme. Now it does detect that I have an internet connection but the ethernet still isn't working on anything. Wi-Fi works all around.
I have found that the ethernet port shows as Self Assigned IP. No internet connection via it but if I turn on and connect via Wi-Fi under Airport Utility it gives me the option to connect to Ethernet which shows an IP and says I'm connected. If I turn off Wi-Fi then the option goes away.
So I'm baffled as to what is causing the ethernet not work on three separate routers and I haven't found anything online that matches with my issue. Any ideas or thoughts?