I have one query with regard to PEM (Power Entity Modules) in Juniper routers. On MX series routers, 4 x PEM Modules are installed.
However in case 1 x PEM is not receiving power (like Input Power Supply is gone ) but PEM itself is physically there then Juniper router reports 2 x chassis alarms , with one being that 'PEM Not Ok' while other 'PEM Input Failure'.
Below is example that I took from Juniper KB (https://kb.juniper.net/InfoCenter/index?page=content&id=KB29614&cat=SRX_5400&actp=LIST)
Only PEMs 0 and 1 are cabled. The result is these alarms:
lab@mx240> show chassis alarms 4 alarms currently active Alarm time Class Description 2014-10-23 17:43:35 UTC Major PEM 3 Input Failure 2014-10-23 17:43:35 UTC Major PEM 3 Not OK 2014-10-23 17:43:35 UTC Major PEM 2 Input Failure 2014-10-23 17:43:35 UTC Major PEM 2 Not OK
In the KB they mentioned the CAUSE like this :-
This may be a hardware issue with the PEM, or an issue with the power supply to the PEM.
and solution they mentioned is like this :- "If a PEM was cabled, but the circuit breaker was shut off, or the PEM was not receiving any voltage for some other reason, the same alarms and show chassis power output would be seen. It is important to verify that the PEM is receiving the correct voltage (which may require an electrician) before assuming it is a hardware issue with the PEM"
How could we distinguish between two cases? How could we know that whats the real fault? Is it PEM become faulty (PEM Not Ok) or is it input to PEM gone?
We have to extend the such alarms to both Network Field Team and Power Team and hence this distinguish is necessary. In case PEM Input Not OK , the power team will take action and would fix the source. and in case PEM went faulty, Network field team guys will inspect and replace PEM Module.