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Tx Power Low


I am having some problems getting a stable connection after upgrading some interfaces from 1000BaseSX to 10GBase-LRM on our network.

The connections are between a 4900M switch (X2-10GB-LRM) and 3750X switches (SFP-10G-LRM), over Multimode fiber (and using mode conditioning patch cables).

I am seeing the following error being logged.

%SFF8472-5-THRESHOLD_VIOLATION: Te1/1/2: Tx power low alarm; Operating value: -40.0 dBm, Threshold value: -10.5 dBm.

The 4900M is running 12.2(54)SG1 and the 3750X is running 12.2(58)SE.

It is also showing up on a number of the connections throughout the network and there are a high number of input/CRC errors on the interface.

Running the following command shows that the Optical Transmit Power is below the threshold as suggested by the log.

#show int Te1/1/2 transceiver detail

ITU Channel not available (Wavelength not available),

Transceiver is internally calibrated.

mA: milliamperes, dBm: decibels (milliwatts), NA or N/A: not applicable.

++ : high alarm, +  : high warning, -  : low warning, -- : low alarm.

A2D readouts (if they differ), are reported in parentheses.

The threshold values are calibrated.

                              High Alarm  High Warn  Low Warn  Low Alarm

          Temperature         Threshold  Threshold  Threshold  Threshold

Port       (Celsius)          (Celsius)  (Celsius)  (Celsius)  (Celsius)

--------- ------------------  ----------  ---------  ---------  ---------

Te1/1/2    30.7                75.0        70.0        0.0      -5.0    

                              High Alarm  High Warn  Low Warn  Low Alarm

           Voltage            Threshold  Threshold  Threshold  Threshold

Port       (Volts)            (Volts)    (Volts)    (Volts)    (Volts)

---------  ---------------    ----------  ---------  ---------  ---------

Te1/1/2    3.20                  3.63        3.46        3.13      2.97 

           Optical            High Alarm  High Warn  Low Warn  Low Alarm

           Transmit Power     Threshold  Threshold  Threshold  Threshold

Port       (dBm)              (dBm)      (dBm)      (dBm)      (dBm)

---------  -----------------  ----------  ---------  ---------  ---------

Te1/1/2    -40.0                3.5        0.5        -6.5      -10.5    

          Optical            High Alarm  High Warn  Low Warn  Low Alarm  

          Receive Power      Threshold  Threshold  Threshold  Threshold

Port      (dBm)              (dBm)      (dBm)      (dBm)      (dBm)

-------    -----------------  ----------  ---------  ---------  ---------

Te1/1/2    -7.6                3.5        0.5        -8.0      -12.4

Any suggestions on what the issue might be? Transceiver problem? Cabling issue?

Thanks for your help.

InayathUlla Sharieff
Cisco Employee


The Tx power low alarm message are generated when the Optical Transmitted Power is less than required or when the monitoring done by

on-transceiver hardware is not reading the values properly. Usually that indicates a problem at L1 or that we are exceeding the distance limits.

If there is any patch panel in between the line on fiber?

 X2-10GBase-LR is a long reach module, however you are using a fiber cable of

35 - 50 feet distance long.

You should use an optical attenuator to prevent damage. LR (long reach)

modules are intended for cables that are multiple kilometers long. The

maximum distance for LR is 10 km, versus the SR (short reach) module, whose

maximum distance is 300 m.

Please follow the next steps in order to continue troubleshooting the issue:

 1.       Could you please try Reseating the transceiver and fiber cable.

2.       If you have another transceiver, let's try to swap it out to see if the messages stop. If they do, then we have a faulty transceiver.

3.       If the message continues after the replacement, let's try changing the fiber please.

4.       Can you try to connect the same cable to other interface and check the issue?




We are using LRM not LR optics. 10GBASE-LRM supports distances up to 220m.

The distance between the switches is around 40-50 meters. There are mode conditioning patch cables from the switches to the fibre patch panels in the building.


Had this problem too, when connecting 3750X to 6506E via 10G links.

Solved it by downgrading to stable IOS on 3750X (from 15.2(2)E to 15.0.2 SE8).

Problem is on TX side, not on RX side; SFP is instructed by IOS to transmit on very low power, it is not the issue with cabling.

Hope it works for you too.

Hi, I'm experiencing a similar issue,  did the solution of down grading the image have any impact?