What is a loopback adapter?


Installers and network technicians have a lot of unique tools on hand for any number scenarios. These can range from $450 line testing equipment to $100 label machines. One tool that is a mainstay for any sort of network deployment is the RJ45 Loopback Adapter. This little tool is slightly larger than a keystone jack but can provide invaluable information about a connection.


How does a Loopback Adapter function?

Getting into how a device works we’ll find out this is one of simplest tools out there. Ethernet uses pairs of wires to Transmit (TX) and Receive (RX) data and information. A traditional 100BASE-TX connection requires only two pairs to function while a 1000BASE-TX connection will require all four pairs. By taking the TX pair and hooking (or looping) them into to the RX position we can create a closed loop which should tell the device the connection is active.


Using the loopback adapter

For our test I have a simple network set up containing a run a solid cat6 cable which is about 10FT long. It’s terminated with a cat6 keystone jack on one end and punched down into a 24 port cat6 patch panel. Then we have a small cat6 patch cable connecting the switch and the patch panel together. The loopback adapter has both a jack and a plug so it can be plugged directly into the keystone jack or, if the jack is in a hard to reach location, can be plugged into a patch cable using the other end.


The Results

What should you expect after plugging the adapter in? It’s quite simple. Either the connectivity light on your device will light up or it won’t. Connectivity light means the connection works and you can move on to the next one. If there is no light, then there might be an issue with the connection that requires further investigation.

Some smart switches have built in loopback protection and this will stop a loopback adapter from working properly. This can be disabled on some switches.



Whether you are a fresh-faced network tech, or a battle-hardened systems administrator one thing is for certain: a loopback adapter is a must have tool for quick and easy network testing. These tools offer the most basic of testing but when time is of the essence, quickly isolating network issues becomes invaluable.