How to edit threshold values for optical links?

Matthew Matheus · ‎01-11-2013

I have a switch where the current power threshold is set to -20.0db. The problem is that the receive power fluctuates between -19.9db to -20.1db, which is causing it to throw alarms on my solarwinds monitoring server. What I would like to do is change it to a different warning threshold, but I can't seem to find the command to do so.

This is a catalyst 3750 running IOS version 12.2(55)SE3

Here is an example of the output in question:

DC_3750#sh interface g1/0/1 trans detail

ITU Channel not available (Wavelength not available),

Transceiver is externally 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)

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

Gi1/0/1 40.9 110.0 93.0 -3.0 -9.0

High Alarm High Warn Low Warn Low Alarm

Voltage Threshold Threshold Threshold Threshold

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

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

Gi1/0/1 3.24 4.00 3.70 2.90 2.80

Optical High Alarm High Warn Low Warn Low Alarm

Transmit Power Threshold Threshold Threshold Threshold

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

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

Gi1/0/1 2.9 8.1 7.0 -2.0 -4.0

Optical High Alarm High Warn Low Warn Low Alarm

Receive Power Threshold Threshold Threshold Threshold

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

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

Gi1/0/1 -20.1 - 0.7 -1.0 -20.0 -24.1

Marvin Rhoads · ‎01-12-2013

You cannot modify the power levels that are built into the transceiver (or more specifically IOS and associated MIBs supporting the transceiver) that trigger warnings and alarms.

While you could change the SolarWinds NPM setup to not manage that resource, it would defeat the purpose of the tool.

In reality -20.0 dBm is a generous threshold and if you are regularly seeing receive power levels that low you should consider evaluating the use of the optical span and either:

a) taking steps to improve it (e.g. are all your spans OM3 or better fiber etc. if multimode, inspecting and cleaning all patch locations' ferrules) or

b) looking at things like extended reach optics if it is a single mode span.

Hope this helps.

Matthew Matheus · ‎01-14-2013

That is quite helpful, however I have a bit of confusion, as the other end of the link has a threshold of -40db. Both ends of the link are using ZX transceivers, so why the difference in thresholds?

Marvin Rhoads · ‎01-14-2013

-40 dBm - really? That's astonishingly low.

The data sheet I am looking at (Table 2 here) for Cisco ZX SFP transceivers indicates -3 to -23 dBm as the receive power range rating.

Can you please tell me the model of transceiver you are using (excerpt from "show inventory" or "show inventory detail" depending on your platform)?

Matthew Matheus · ‎01-16-2013

Here is the inventory detail:

NAME: "GigabitEthernet1/0/51", DESCR: "1000BaseZX SFP"

PID: Unspecified , VID: , SN: ECL1447036A

Here is the thresholds on that interface:

show interface g1/0/51 trans detail

ITU Channel not available (Wavelength not available),

Transceiver is externally 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)

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

Gi1/0/51 26.3 95.5 90.5 -9.4 -44.4

High Alarm High Warn Low Warn Low Alarm

Voltage Threshold Threshold Threshold Threshold

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

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

Gi1/0/51 3.25 4.00 3.60 3.00 0.00

Optical High Alarm High Warn Low Warn Low Alarm

Transmit Power Threshold Threshold Threshold Threshold

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

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

Gi1/0/51 3.0 8.0 6.0 -1.0 -3.0

Optical High Alarm High Warn Low Warn Low Alarm

Receive Power Threshold Threshold Threshold Threshold

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

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

Gi1/0/51 -1.1 0.0 0.0 -40.0 -40.0

Marvin Rhoads · ‎01-17-2013

That Gi1/0/51 interface transceiver detail output in your last output above looks odd. The Optical Receive Power low warn and low alarm thresholds are the same. Also, -40 dBm is usually what is reported by Cisco transceivers when no signal is detected.

Is is possible that that particular interface is not a genuine Cisco transceiver?

This is diverting a bit from your original question. Given the first transceiver's built-in threshold, you cannot override that. It is programmed in based on the device's ability to reliably convert the received optical signal to usable bits for the MAC layer to process.