[Cisco] informal workaround for Bug CSCvg59274 “ASR9901 FAN Problem”

I found out the way to recover from the situation of Bug number “CSCvg59274“.

It’s still informal workaround but I think this is the only way without affectin the connection.

[phenomenon]
This is exactly we faced on our lab.
– – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – –
1. Remove the FAN of the three.
2. Wait for about one minute.
3. Inserted it back, LED of the FAN got green but soon it’ll be blank.
4. Type “admin show env fan” and it shows speed is blank[-]
5. You can see the following message.
  Fan Speed Sensor 0 has raised an alarm for device error
5. The other two fan’s speed is so high like 15000.
– – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – –

[Verification]
If you plug out and in FAN immediately like within 30 seconds,
the status of FAN will be normal by LED and CLI.

But about 60seconds has passed and other FAN’s speed gets high(10000 – 15000rpm),
the FAN you plug in will be abnormal status.

The LED may get green temporary but it will be blank soon.

[informal workaround]
This is awesome discovery by coincident.
You will need to take full responsibility for your action.

Assume the following situations.
There are three FANs in the rear side of Cisco ASR9901.
FAN0 is the one you face the “CSCvg59274”
FAN1 and FAN2 are normal.

– – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – –
(1) The LED of FAN0 is blank and the speed of FAN1 and FAN2 is so quickly because of CSCvg59274.
(2) Unplug the FAN0 to make it semi-inserted. Of course it’s not recognized by ASR9901.
(3) Unplug the FAN1 or FAN2(just choose one of the normal FANs) to make it semi-inserted.
I choose FAN1 this time as an example.FAN1 is not recognized by ASR9901.
(4) Plug the FAN0 completely.
(5) Plug the FAN1 completely.
(6) The FAN1 will be normal soon.
(7) The LED of FAN0 will be green after a while

– – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – –

The key point is you need do from (3) to (5) very quickly.
Maybe within 5 seconds.
Make sure you insert them back very quickly because if only one FAN is working,ASR9901 will be off automatically.
I’m not sure it’s because of IOS XR Release 6.4.1.
But it’s the fact Cisco ASR9901 no longer is able to work with only one FAN.

If you see the following error messages,check the CSCvg59274 and this article again.
PKT_INFRA-FM-4-FAULT_MINOR : ALARM_MINOR :sensor in a failure state :CLEAR :0/FT2: Fan Speed Sensor 0 has raised an alarm for device error

– – – – – – – – – – – – – – – – – – – – – – – – – – – – –
https://bst.cloudapps.cisco.com/bugsearch/bug/CSCvg59274
– – – – – – – – – – – – – – – – – – – – – – – – – – – – –

I’m not sure if this operation is good.
I hope Cisco will update about this bug soon.
I will update here if I get more information.

Another way to resolve this bug is only rebooting(power off and power on) ASR9901 I guess.

[2019/03/05]
The operation flow.

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