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Do you ever find yourself needing to know whether an ethernet port will light up without actually hooking it up to a switch. Or, do you need to know what port on a switch a certain jack is plugged in to. Lucky for you, it’s really easy to make your own ethernet loopback cable.

To start, you’ll need a couple of tools: a wire cutter and a wire stripper. You’ll also need some electrical tape. And, last you’ll need an ethernet cable that you don’t mind cutting up.

Steps:

  1. Cut about 12" off of the end of the cable
  2. Strip off about 2" of the outer insulation
  3. You should see 8 wires paired up (Orange, White-Orange, Green, White-Green, Blue, White-Blue, Brown, and White-Brown). Un-twist each pair.
  4. Strip about an inch off of these four: White-Orange, White-Green, Orange, and Green
  5. Wrap the exposed wires together matching White-Orange to White-Green and Orange to Green
  6. Cover the exposed wire with electrical tape
  7. You can ignore the other 4 wires
  8. Plug the cable into either a network card or a switch. If it was done correctly the link light should light up.
  9. Wrap the end of the cable with tape to "neaten" it up a little
  10. Of course, you’ve still got the other end of the cable, so you might as well make another

I’ve seen this around the internet for anywhere from 5 bucks to 50 bucks. So, aside from the cost of a few feet of tape, a spare ethernet cable, and some time; you’ve saved yourself 50 bucks (or 100 if you made two :-) )

9 Responses to “DIY: Make Your Own Ethernet Loopback Cable”

  1. mike

    so if i want to have a LAN IP to ping a virtual machine on my computer, i will need a loopback cable? cause overwise without a cable in my ethernet slot, i keep geting “media disconnected” in CMD

    Reply
    • sean

      What???
      Why would you interface a virtual machine with a loopback directly? If the host machine has no working NIC, what would a loopback cable do?

      Reply
  2. Ryan

    Never done anything with a virtual machine that needed a network connection to the main computer. I would assume they already had some type of virtual connection built in. Or at least a way to share files between the virtual machine and your actual machine.

    Reply
  3. robert

    Clear, concise instructions. And they work! Who could ask for anything more.

    Reply
  4. Robert

    On standalone Windows XP computer, I can plug this wrap cable into the ethernet port, type IPCONFIG, and see my static IP address. However, under Windows 7, IPCONFIG shows no IP addresses. How can I get Windows 7 to show my static IP address?

    Reply
    • Ryan

      Why worry about the IP on a computer not attached to a network?

      If it’s static, it should show up in the control panel.

      Reply
      • Robert

        For the purpose of checking out an ethernet cable, the system is standalone. Normally, however, it is connected to another computer. The wrap is actually made in a socket where the ethernet cable plugs in. To experiment, I made a wrap cable about 6 inches long.

        If IPCONFIG shows the static IP address, the cable is good. Otherwise, the cable is bad.

        After posting the above, I forgot to bookmark your site.

        The problem was not with Windows 7, but with the length of the wrap cable I was using to experiment. The Windows 7 ethernet card supported 1 GB/sec while the XP ethernet card only went up to 100 MB/sec. Configuring the Windows 7 ethernet to max out at 100 MB/sec solved the problem.

        Does an ethernet card have a way to measure the cable length?

        Reply
        • Ryan

          It’s not distance. It’s the gb vs 100. This is a 100 crossover. Gigabit crossovers are a bit different.

          Reply

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