When I'm at home I use two general-use computers: a desktop (iMac manufactured Late 2013 running macOS Sierra v. 10.12.6) and a laptop (MacBook Pro manufactured mid-2012 running the same OS as the desktop). I don't use WiFi at home; both computers connect to the internet with a wire. I use the same wire with both computers, detaching and re-attaching one end of it.
Until a few days this worked smoothly, but then the wire's little plastic clasp broke, and I replaced it with a new wire (PATCH CORD CAT .5E FTP STRANDED 26AWG 4 PAIRS TIA /EIA 568A). Now when I attach the wire to one of the computers after it has been attached to the other computer, the newly attached computer doesn't connect to the Internet, even after 5 minutes' wait.
Only after restarting the router (i.e. unplugging it from the outlet, waiting 30 seconds, replugging it, and waiting some 3 minutes) does the Internet connection re-establish. (If I detach the wire from the computer and then reattach it to the same computer without connecting it to the other computer in-between, the Internet connection is established automatically.)
How can I get my computers to behave as in the past, when all I needed to do in order to connect a computer to the Internet was to attach the wire to it?
A partially successful attempt to solve the problem
- On computer A, while connected to the Internet, I opened Settings > Network.
- I took a screenshot.
- I changed the "Configure IPv4" item from Using DHCP to Manually.
- I filled-in the settings as they were captured in the screen cap.
- I clicked "Apply". The Internet connection remained intact.
- I detached the wire from computer A, and attached it to computer B.
- I repeated steps 1-5 on computer B, except instead of taking a new screen cap, I used the one from step 2, so that the settings on both computers were the same. Computer B was unable to connect to the Internet with these settings.
- I detached the wire from computer B, and attached it to computer A. After a few seconds, computer A connected to the Internet automatically.