Commands for troubleshooting SFP optical levels OTDR test

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Commands for troubleshooting SFP optical levels OTDR test:To troubleshoot a link flapping port that has been err-disabled, use these diagnostic tools to isolate whether the fault lies in the fiber optics or the copper cabling.

Fiber Troubleshooting: SFP Optical Levels


Use Digital Optical Monitoring (DOM) to check the “light levels” of your fiber transceivers. This identifies if the signal is too weak (dirty fiber/long distance) or too strong (blinding the receiver).
Command: show interfaces transceiver detail.


What to look for:


Rx Power (Receive): The most critical metric. For standard 10G-SR, it should

Command: show interfaces transceiver detail.


What to look for:


Rx Power (Receive): The most critical metric. For standard 10G-SR, it should typically be between -2 dBm and -9 dBm.


Tx Power (Transmit): Shows the strength of the laser leaving the switch. If low, the SFP itself may be failing.


Alarms/Warnings: Look for ++ (high alarm), + (high warning), – (low warning), or — (low alarm) next to the readings.


Common Fix: Clean the fiber tips and SFP ports with a fiber cleaning kit.

Read also: [Solved]link flap cisco switch port error disabled

Copper Troubleshooting: Cable TDR Test


The Time-Domain Reflectometer (TDR) test can detect physical faults (shorts or breaks) in copper Ethernet cables and even tell you how many meters away the fault is.


Step 1: Start the test


bash
test cable-diagnostics tdr interface

Step 2: Wait 5–10 seconds, then view results


bash
show cable-diagnostics tdr interface

Interpreting Results:


Normal / Terminated: The cable is healthy and connected.


Open: The cable is broken or unplugged at the distance shown (e.g., “Open at 15 meters”).
Short: Two wires in the same pair are touching, likely due to a crushed cable or bad crimp.

Verify Hardware Recognition


If an SFP isn’t showing any data, confirm the switch actually recognizes the hardware:
Check Inventory: show inventory (look for the SFP’s serial number and PID).
Check Logs: show logging | include transceiver to see if the switch rejected an “unsupported” third-party module

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