What is the cause of high utilization of cpu on fpc.Below is the output of which depicts utilization as 99 but router is running just fine.

show chassis fpc 
                     Temp  CPU Utilization (%)   Memory    Utilization (%)
Slot State            (C)  Total  Interrupt      DRAM (MB) Heap     Buffer
  0  Online            69     99         14       512        17         43
  1  Online            69     99         14       512        17         43

But on the other hand routing-engine showing CPU as 94 percent idle.

show chassis routing-engine 
Routing Engine status:
    Temperature                 52 degrees C / 125 degrees F
    DRAM                      1536 MB (1536 MB installed)
    Memory utilization          35 percent
    CPU utilization:
      User                       4 percent
      Background                 0 percent
      Kernel                     2 percent
      Interrupt                  0 percent
      Idle                      94 percent
    Model                          RE-ACX-2100
    Serial ID                      xxxxxxxxxxx
    Start time                     2017-12-20 16:18:07 PKT
    Uptime                         510 days, 12 hours, 52 minutes, 41 seconds
    Last reboot reason             0x1:power cycle/failure 
    Load averages:                 1 minute   5 minute  15 minute
                                       0.18       0.13       0.08

What could be the cause of such high utilization on fpc?
Second what is the difference/significance between two cpu utilizations?

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    Dec 15, 2019 at 2:50

1 Answer 1


The two CPU utilisation figures are for the forwarding plane/line card and the routing engine respectively.

For the control-plane, you can run show system processes extensive to get an idea as to which process is consuming the most CPU on the Routing Engine.

For the forwarding-plane, you'll need to jump on the FPC or FEB depending on your device model. Use start shell pfe network feb0 to open up a session to the forwarding engine on your ACX and then run:

show sched

show threads

to get an indication about what is using all the FPC CPU. It may be that you're doing something like IPSEC or NAT at a high PPS rate.

  • Dear Benjamin i get this error [[May 19 18:43:48.759 LOG: Err] unit 0 START_BY_START_ERR asserted]]. and it is just printed continuesly.
    – Terminator
    May 19, 2019 at 18:44

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