Create Ethernet Loopback Cable with RJ45 Connector

Rashmi Bhardwaj | Blog,BUZZ,Config & Troubleshoot

This article will help us with a small hardware testing tool which helps verify whether the interface port is working or not. The small testing tool is an RJ45 based Ethernet Testing tool which can be created within minutes by connecting wires as per defined below-

Before that, the following are required to make Ethernet Loopback Tester tool

Hardware Prerequisites –


  • Cat5 or Cat6 Cable
  • Crimping tool
  • Cutter
  • RJ-45 Connector

Step 1 –

Remove the jacket of CAT5/6 Cable and cut out one pair (2 Wires) of approx. 4-5 inch length from a total of 4 pairs.

Step 2 –

Follow below pin connectivity –Pin 1 <-> Pin 3

Pin 2 <-> Pin 6

Step 3 –

Crimp the wires in RJ-45 connector through Crimping Tool.

Once the Ethernet Loopback testing tool is ready, let’s verify Ethernet ports on Cisco hardware –

Step 1 –

1st, issue “show interface” command to verify the Ethernet port status. By default the interface output should be – “interface is up and line protocol is down”

Step 2 –

Next, insert the RJ45 testing tool into interface to be verified

Step 3 –

Finally, issue command “show interface” to verify Ethernet port status. The expected output is –“Interface is up and line protocol is down

If the above output is not received, i.e. up/up status, this confirms the interface hardware is malfunctioning.

Related Blogs –

RJ11 vs RJ45

Ethernet Cable vs Patch Cable 




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