Creating or making a RJ45 Ethernet loopback cable/adapter is pretty simple.
Ethernet Loopback Cable / Connector:
A loopback cable redirects the output back into input. This effectively gives the NIC the impression that it is communicating on a network, since its able to transmit and receive communications.
- Cat-5 cable (30cm should be enough)
- RJ-45 connectors
Remove the cable pairs from the cat-5 cable and you need a single pair of approximately 4 inches length per loopback cable.
Next separate the 2 wires at each end of the cable enough to slide into to RJ-45 connector and follow below Pinout details.
Ethernet Loopback cable/connector Pinout Details:
Pin 1 -> Pin 3
Pin 2 -> Pin 6
Next crimp the end cable using Crimping tool. Now RJ45 Ethernet Loop back Cable/Connector is ready.
Using the Ethernet loopback plug with Cisco Routers:
I covered how to use ethernet loopback cable for testing ethernet or fastethernet interfaces on Cisco Routers or Swtiches.
Step 1 Do a “show interface” command on the suspect Cisco ethernet interface. If the interface is up and line protocol is down”
Router#clear int fastethernet 0
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