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Unidirectional link

We have a switch that continues to get unidirectional links. The fiber run is very long and is working off of legacy infrastructure. We have one uplink that can sustain 100MBPS trunk link. However, the moment we plug in the second redundant uplink the port will error disable for unidirectional link. We have tested all of the patch cables involved on the run, replaced the catalyst 3560 v2 switch, and even had a contractor come and out verify the fiber was good between the buildings. No matter what the link will come back as unidirectional. Does anyone have any idea of what this could be? Or any troubleshooting steps we could try next?  We have UDLD port aggressive enabled on both the switch interface and the interface on our distro router.

VIP Super Bronze

Unidirectional link

What type of optics are you using?  Have you replace them?

Unidirectional link

what distances are we talking here? how about the sfp's? are they good?

you might want to do some loopback testing between the switches. I mean put a software or a HW loop on the fibre. is it a DWDM /CWDM , dark fibre?? you can try and isolate which part of the path is causing the problem

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