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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

  1. On computer A, while connected to the Internet, I opened Settings > Network.
  2. I took a screenshot.
  3. I changed the "Configure IPv4" item from Using DHCP to Manually.
  4. I filled-in the settings as they were captured in the screen cap.
  5. I clicked "Apply". The Internet connection remained intact.
  6. I detached the wire from computer A, and attached it to computer B.
  7. 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.
  8. I detached the wire from computer B, and attached it to computer A. After a few seconds, computer A connected to the Internet automatically.
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  • I think it's pretty likely that the wire you have is miswired. Did you wire it yourself or did you buy it preassembled? Are you 100% sure the pins-to-pairs mapping is correct? Oct 2, 2017 at 7:02
  • @DavidSchwartz: I bought it preassembled. There are no pins involved; the connection point looks like one of these.
    – Evan Aad
    Oct 2, 2017 at 7:07
  • It is still possible that by bad luck you happened to get a bad cable. What did the packaging on the cable say? Did it have a category rating? Oct 2, 2017 at 8:33
  • @DavidSchwartz: As far as I recall, the cable was not packaged, or maybe it was inside a nylon bag. What I'll do is, I'll buy a new cable at a different store. Hopefully this will solve the problem. I will report back once I've changed the cable.
    – Evan Aad
    Oct 2, 2017 at 8:40
  • Does the cable have any labeling on it? If not, why do you think it's suitable for your application? Oct 2, 2017 at 8:40

1 Answer 1

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If it really is exactly as you say, it indeed points to the new cable. One more scenario I could see: for ethernet, there are 'straight' cables and such where Rx and Tx are crossed. Up til the early 2000s, the difference did matter, after that, ethernet ports were usually able to guess the right configuration. So maybe the cable is good per se, but between router and macs, guessing went better with the other type.

If that wasn't it, next thing to check would be if dhcp is set to work on both router and macs, unless you know what fixed/static ip is and want to use that. Future helpers will probably benefit, too, if you detail what answers you give to what questions in your step 3.

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  • So what practical advice could you give me to help solve the problem?
    – Evan Aad
    Oct 2, 2017 at 8:54
  • I've changed answer already. But if after sucessfully connecting, you go to settings-network and have the properties of the eth connection displayed, what does it say? What is your ip, and is there a field saying automatic/dhcp OR manual?
    – j.h.
    Oct 2, 2017 at 9:04
  • And, although I might have logged out by the time you read this: what happens if you do not reboot the router?
    – j.h.
    Oct 2, 2017 at 9:16
  • I've added more details to my post. If I do not reboot the router, nothing happens, i.e. the Internet connection does not reestablish automatically, even after 5 minutes' wait.
    – Evan Aad
    Oct 2, 2017 at 9:18
  • But does 2x wizard work without reboot? But first try to give the config of the eth connection when it finally works. You can also log into your router and make sure dhcp is on. It usually is on by default, but who knows. Rebooting and re-running wizards may have lost some setting.
    – j.h.
    Oct 2, 2017 at 9:29

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