Ok, since you have already renamed your two iMacs, let's concentrate on the network settings on both.
For clarity, I will name the Ethernet-connected iMac, as iMacE, and the wireless-connected one: iMacW.
Let's start with iMacE.
- Go to System Settings > Network > Ethernet > Details ... > TCP/IP
- Select Renew DHCP Lease.
- Give it a few seconds, then check the following settings: Configure IPv4 = Using DHCP. Note the values for IP Address, and Router Address. These addresses should start with one of the following: 192,172, or 10. If, instead, it starts with 169, this Mac is not "seeing" the DHCP server in your TP-Link router.
Next, let's work with iMacW. The steps will be similar to what we did for iMacE:
- Go to System Settings > Wi-Fi > Select your Wi-Fi network > Details ... > TCP/IP
- Select Renew DHCP Lease.
- Give it a few seconds, then check the following settings: Configure IPv4 = Using DHCP. Note the values for IP Address, and Router Address. These addresses should start with one of the following: 192,172, or 10. If, instead, it starts with 169, this Mac is not "seeing" the DHCP server in your TP-Link router.
For both iMacs, the IP Address of each should be in the same IP range. For example, if your TP-Link's DHCP server is serving IP address in the 192.168.0.x range, each Mac should be in the same range, but with a different last octet. The Router Address should be the same for both ... and pointing back to the LAN-side address of the TP-Link.
If all of this is good, I would like for you to use the Ping command in the Terminal to "ping" between these two iMacs to see if there are any issues with them communicating with each other. I would like for you to ping them from both directions. That is, from iMacE to iMacW, and then, from iMacW to iMacE.
To do so, starting with either iMac, run the Terminal app which is located in the /Applications/Utilities folder. At the Terminal's command prompt, enter: ping -c3 <enter the IP address of the other iMac>, and then press return.
A successful ping would have 3 transmitted & 3 pings received with 0% packet loss. Anything else would indicate an issue with your network. Please repeat this from the other iMac.
It should look something like the following:
Please post back your results.
