Make your own Ethernet Loopback connector

Occasionally I have the need for a network card to operate as though it has a live network connection, without it actually being connected to a network. Typically for testing purposes, and occasionally for specific software configurations. To do this I needed a quick and easy way to make a loopback connector. Something small enough to keep in my PC toolkit, yet large enough that it wouldn’t be lost. Mine ended up about the size of a ballpoint pen. The following is a quick “how to” for making an Ethernet loopback connector.

To build this particular loopback connector you will need one (1) spare Category 5e (cat5) cable.

  1. Cut 4 or 5 inches of the end off a network cable, keeping the connector intact.
  2. Cut away two inches of the main sheath covering the eight wires. (Be careful not to cut the wires inside.)
  3. Cut the sheath on Orange-White (2) and Green (6) and twist them together. Tape this pair. (Soldering is optional and preferred)
  4. Cut the sheath on Green-White (3) and Orange (1) and twist them together. Tape this pair as well. (Soldering is optional and preferred)
  5. Leave the other four wires alone. (Optionally tape these down to prevent cross talk*)
  6. Tape the end down to make it look presentable.
  7. Plug RJ-45 plug into your Network Card.

*For a Gigabit Ethernet Loopback you will also need to connect the other four wires as follows:

  1. Cut the sheath on Blue-White and Brown-White and twist them together. Tape this pair. (Soldering is optional and preferred)
  2. Cut the sheath on Blue and Brown and twist them together. Tape this pair as well. (Soldering is optional and preferred)

Updated April 19, 2011 – Added Gigabit Loopback Information.