I have a 6503 running 12.2(18)SXF5 with a SUP-720. In slot 3, we have a 16-port WS-6516A GBIC line card. In each port we have a WS-5486 GBIC plugged into it.

I cant get 2 of the gigabitethernet interfaces to come up. So, while the field techs troubleshoot the fiber patches, I wanted to try to run port diagnostics on my end. Is there a way to loopback an ethernet interface as we can with a serial interface? With a serial/T1 interface, for example, you can plug in a hard loopback plug with pins 1 looped to 4 and 2 looped to 5. Or you can run software loopbacks from the onboard CSU/DSU.

What about the ethernet port? Can I use a hard loopback plug? If so, what should the encapsulation be set for? Are there any software dignostics/loopback tests?

Im doing my own research on Cisco's website, but I thought I would put this question out to everyone for a possible quick answer and feedback.

Thanks, folks.