Troubleshooting Fiber Cables

[keinpesto]

There is a single mode optical fiber cable in our datacenter going from a Cisco N5K to another N5K across different racks. The link appears to be dead and I'm hoping to fix it, but I have little to no experience with fiber.

The LED light of the SFP+ ports on both switches are off (not lighting up). What I've tried so far:

• Successfully sent lights end-to-end through the cable.

• Verified the port configurations and made sure that the ports were not in shutdown state.

• Changed the SFP transceiver module + SMF cable to a new port on one of the N5Ks. As soon as I connected this to an unused port, the light went from orange to off. So I verified the Cisco N5K troubleshooting whitepaper which indicates that LED in off states means that the transceiver module may not be receiving power or has been manually disabled.

• Purchased a new transceiver module, connected the SMF cable to it; the LED lights are still off on both ends.

Any ideas on what I should try next? Thanks.

[Leo Laohoo]

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@keinpesto wrote:

There is a single mode optical fiber cable in our datacenter going from a Cisco N5K to another N5K across different racks.

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Single mode from one rack to another?   Is the horizontal cabling multi-mode?

[marce1000]

        >...

• >Successfully sent lights end-to-end through the cable.

               What do you mean by that ? How was that accomplished ?

 M.

[reccon]

Sometimes it happens that the signal at the receiver is too bad.
Then the LED at the SFP module stays off as well.

You can check that with the command
"sh int transceiver"
(on both sides/switches)

You will get al result like this
Port Temperature Voltage Tx Power Rx Power
--------- ----------- ------- -------- --------
Te1/1/1 40.8 3.23 -2.2 -2.5

Compare the RX Power result you get with the specifications of your SFP+ module.

If you have a RX Power value of -40 that means the receiver doesn't get a signal at all.

[GEORGIOSBEKOS]

Can you please share the type of SFP, type of connector LC/PC , SC/PC .....

Also try to change Tx, Rx from one side even if fiber are duplex.

Best regards.