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Beginner

Rx power high warning

Hi,

 

I have an Rx power high warning message in my router.

can I leave my router running with this message as it's just a warning or should I install an attenuator because in the long run the router will be damaged?

 

I use multimode fiber and SFP

 

Regards,

2 ACCEPTED SOLUTIONS

Accepted Solutions
Hall of Fame Master

Re: Rx power high warning

The underlying problem should be addressed. or it will eventually cause the SFP to fail prematurely.

 

In my experience however that's a very unusual situation for a multimode fiber connection. Usually the transmit power isn't such that it will over-run a receiver.

 

Can you share the output of "show interface transceiver detail" for the affected interface?

Hall of Fame Master

Re: Rx power high warning

Ah OK, that's more normal to see with singlemode.

 

From the output, you are in the "warning" and not "alarm" range so it is relatively safe to continue operating like that. If it were my network and that was an important link , I'd put a 5 dB optical attenuator inline.

 

If you're US-based.,m you can pick one up via Amazon for US$5.99.

https://www.amazon.com/Fiber-Attenuator-Singlemode-Simplex-Fixed/dp/B001B1HOOM

 

8 REPLIES 8
Hall of Fame Master

Re: Rx power high warning

The underlying problem should be addressed. or it will eventually cause the SFP to fail prematurely.

 

In my experience however that's a very unusual situation for a multimode fiber connection. Usually the transmit power isn't such that it will over-run a receiver.

 

Can you share the output of "show interface transceiver detail" for the affected interface?

Beginner

Re: Rx power high warning

i was wrong, I use a monomode SFP and fiber

 

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)
--------- ------------------  ----------  ---------  ---------  ---------
Gi1/0/25    27.3                89.0        85.0        -5.0       -9.0

                              High Alarm  High Warn  Low Warn   Low Alarm
           Voltage            Threshold   Threshold  Threshold  Threshold
Port       (Volts)            (Volts)     (Volts)    (Volts)    (Volts)
---------  ---------------    ----------  ---------  ---------  ---------
Gi1/0/25   3.29                  3.60        3.50        3.10       3.00

           Optical            High Alarm  High Warn  Low Warn   Low Alarm
           Transmit Power     Threshold   Threshold  Threshold  Threshold
Port       (dBm)              (dBm)       (dBm)      (dBm)      (dBm)
---------  -----------------  ----------  ---------  ---------  ---------
Gi1/0/25    -5.6                 1.0        -3.0        -9.5      -13.5

           Optical            High Alarm  High Warn  Low Warn   Low Alarm
           Receive Power      Threshold   Threshold  Threshold  Threshold
Port       (dBm)              (dBm)       (dBm)      (dBm)      (dBm)
-------    -----------------  ----------  ---------  ---------  ---------
Gi1/0/25    -0.2         +       1.0        -3.0       -19.0      -23.0


Hall of Fame Master

Re: Rx power high warning

Ah OK, that's more normal to see with singlemode.

 

From the output, you are in the "warning" and not "alarm" range so it is relatively safe to continue operating like that. If it were my network and that was an important link , I'd put a 5 dB optical attenuator inline.

 

If you're US-based.,m you can pick one up via Amazon for US$5.99.

https://www.amazon.com/Fiber-Attenuator-Singlemode-Simplex-Fixed/dp/B001B1HOOM

 

VIP Expert

Re: Rx power high warning

I recall (?) asking Cisco about this, and was told, physical damage isn't likely but the receiver could "misread" an overpowered RX.

Normally, as Marvin notes, this isn't an issue on low powered optics. What kind of SPF? What's the fiber cable length?
Beginner

Re: Rx power high warning

I use an 1000BaseLX GLC-LH-SMD SFP with 2 meters of fiber

 

 

VIP Expert

Re: Rx power high warning

2 meters is often quoted as a minimum, but I'm unable to find real confirmation via standards.

If you can obtain an attenuator, for $6 dollars, I would seriously consider Marvin's suggestion to install one. That would seem an inexpensive way to get your power level within spec.

Beginner

Re: Rx power high warning

it's ok

thanks everybody

Highlighted
Beginner

Re: Rx power high warning

this isn't an issue on low powered optics. What kind of SPF? What's the fiber cable length?

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