I have an alarm showing up on an MX480 after removing unused PEMs: "PEM 2 Absent". The mx480 only has 2 FPCs populated, which keeps it fully redundant with 2 PEMs online (each zone is 25%). However, I would like to clear the alarm showing up so it stops triggering our monitoring system, and I am not having luck finding documentation on clearing it. It looks like the mx480 only allows clearing of fpc alarms (no "clear chassis alarms", etc). I appreciate the help.


I understand from your query that in your Juniper MX480 box , you are currently running MX480 with 2 x PEMs installed and the third one which was installed previously has been removed. The MX480 is equipped with only 2 x FPCs.

The problem you face is that in the chassis alarms it shows 'PEM 2 Absent' but this keeps bothering your network monitoring station.


Based on your situation , I guess the reason you are seeing 'PEM 2 Absent' in chassis alarms is that when you initially power on the Juniper MX480 , it was having 3 x PEMs while fourth PEM was not there. Since the chassis initially didn't boot up with fourth PEM from the beginning , it didn't mention fourth PEM in chassis alarms because it knew when it was powered on , it has only 3 x PEMs working.

Now you removed the third PEM while chassis was powered on. As this moment , system is thinking that I was online with 3 x PEMs installed but now third PEM is removed , and it starts reporting in chassis alarms.

To get rid of chassis alarms , you could try to reboot the Juniper MX480 (in a maintenance window) if you chassis alarms / traps are bothering NMS. When you reboot the MX480 , the system will believe that it now has 2 x PEMs initially installed after powered on , hence will not report the third PEM missing.

Below is the command to reboot whole chassis :-

user@MX480> request system reboot both-routing-engines 

Alternatively , you can power off both REs , then power off PEM Modules and then turn on PEM Modules to get router on back.

user@MX480> request system power-off both-routing-engines 

I am not sure whether it will work or not but lets give it a try.

  • Thanks, I was afraid that might be it.. but still a better solution than having the PEMs reinserted. Thanks, I will give it a try! – The Original AI Oct 14 '20 at 4:41
  • @TheOriginalAI. Please accept my answer if it is right – NABEEL NASIR Oct 14 '20 at 4:42

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