How To Create Ethernet RJ45 Loopback Adapter

By | 2011/08/03

I’ll show you how to create an ethernet loopback adapter!

A loopback adapter is useful for tricking a network card into believing it is plugged into a network.


Using two wires, connect:

1 to 3
2 to 6


The pin arrangement is 1-8 left to right, with the flat side facing you.

Here are some pictures to illustrate:

01_loopback 02_loopback

Cool!

5 thoughts on “How To Create Ethernet RJ45 Loopback Adapter

  1. Fath

    Hi…

    Yes, but it is only for _non_ gigabit ethernet; most PC/laptop now equipped with the gigabit one. I can’t get it right for my laptop… After some googling, I found the “right” loopback cable wiring for gigabit ethernet, add these: pin 4 connected to pin 7, and pin 5 to pin 8.

    Sadly, it still not working for me; dunno, maybe the RJ-45 not good quality enough?

    And yeah, some of those website tell us to keep the twisting, it is said for lessen the interference from another pair/cable. I try both (I let twisting, and I use exactly as your picture). Both still not working on my gigabit ethernet.

    Reply
    1. Tim

      Fath,

      You probably need to turn off NEXT (Near End Crosstalk) on your Gig-e card.

      Reply
  2. JunLi

    it still not works either on 100M NIC or 1G NIC
    there is just sending packets, no receiving packets , Could you tell me why
    Thank you

    Reply
  3. JunLi

    it still not works either on 100M NIC or 1G NIC
    there are just sending packets, no receiving packets , Could you tell me why
    Thank you

    Reply

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