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Link down on one side and up/up on the other

dbuckley77
Level 1
Level 1

So we have two switches going over a fiber link.  One side is showing up/up and the other is showing down.  Both are hard coded to 100/full.  One side is going through a media converter that has been tested.  The side that is up/up cannot see far end as cdp neighbor or ping across link.

6 Replies 6

Bilal Nawaz
VIP Alumni
VIP Alumni

The provider of that fiber link (if its not you who own the fiber) may have their equipment enabled to transmit light on one side, even if the link is down? I usually leave fiber to negotiate itself rather than hard code, unless its on a nexus using specific SFP's.

Bilal

Please rate useful posts & remember to mark any solved questions as answered. Thank you.

We own the fiber.  This is how it goes:

 

Side a switch to 10/100 media converter via copper ethernet patch cable.  Fiber patch cable to fiber patch panel.  Back of fiber patch panel goes underground via single mode fiber across town (about 3 miles give or take).  that single mode fiber hits a fiber patch panel at site B.  Front of fiber patch panel has fiber patch cable directly to switch.  

 

This is just the last hop in a 4 hop link that we're troubleshooting.  We already proved out the first three hops and they would not work when set to auto, only when hard coded to 100/full at both ends. 

Is the side that is UP/UP the copper side, the media converter may possibly be leaving one side up? I wouldn't rule out a potential fiber break either. Also where the fiber patch goes to the switch have you tried changing the polarity?

Please rate useful posts & remember to mark any solved questions as answered. Thank you.

Yes, the side that shows up/up is the side with the media converter and the copper to the switch.  I have tried flipping the fiber pair at the end where the fiber hits the switch and it took the link down completely.  I'm thinking the issue is most likely something wrong with the fiber on this hop of the link.

It appears you are you are only using media converter to convert the physical medium and not the speed since you have hardcoded both side with 100mb. So, I am assuming both interfaces can support upto 1gig because in that case auto-negotiation won't work as media converter only supports 10/100, and if both interfaces can only support upto 100mb then you don't need to hard code them.as media converter will take care of that.

 

Lot of times just looking at the laser with a naked eye you can tell the difference if one is brighter then the other (caution - they say it can affect your eyesight ;), I would look/test at the laser that's coming from the remote end to media converter and then look at the laser that's going back to the remote end. Also, if there is any unused fiber interface on a switch or if you have a pc with a fiber nic that supports 100 mb I will just directly plug it there to rule out a faulty media converter.

 

 

clappen
Level 1
Level 1

Hi, I had the same problem and I found this topic with google. In my case the solution was to add this command on the interface:

speed nonegotiate

 

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