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[Junos] How to check console port rate

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Article ID: KB34747 KB Last Updated: 27 Sep 2019Version: 1.0
Summary:

For kernel, messages/hostbound traffic via em0/em1 interfaces, electric noise/keyboard input/storm from console port are all treated as interrupts. High interrupt input can be impactful because it has the highest priority in kernel processing and may starve other processes.

Note: Interrupt is an important part of kernel processing and console port is one source of interrupt.  Console is normally treated as the “last resort” when other access methods  are not working. Most users keep it connected but lightly used.

For em0/em1 interface statistics, we can issue 'show interface em0/em1 extensive' to determine/compare if the rate is normal or not. Depending on the driver and platform, the console port can have different names such as uart, sio, irq .etc. This article helps to determine if there’s any current/previous console interrupt storm caused by external factors such as cable/terminal server.

Solution:
  1. Identify the console interface name

    root@user-re0> show system boot-messages | match console 
    uart0: console (9600,n,8,1) 
  2. Check interrupt total count/rate

    > show system virtual-memory
    ...
    interrupt        total       rate
    irq4: uart0      3976        0 <-- lightly used console
    irq14: ata0      401699      2
    ‚Äč

When unusually high total interrupt/rate is observed with light/no usage of console, check the external factors such as term server/console cable.

irq4: uart0          114462750     0 <-- Total is high for a management port. If it’s not frequently used, then it indicates an external issue.

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