Some times the alarm 'CB 19.44 MHz clock failure' alam reported on an MX router and no clksyncd core dump is generated. This article explains how we can verify the health of the clock.
show chassis alarms
Apr 28 01:53:48
1 alarms currently active
Alarm time Class Description
2024-04-21 16:03:20 UTC Major CB 0 19.44 MHz clock failure
Control board (CB) on MX Chassis is responsible for providing clocking for the MPC line cards. In the event of hardware failure of clocking mechanism on CB, MPC cards can lose the clocking source.
Following procedure can be used for verifying the clock status of CB.
Step 1 :-
Check the register values. Sometimes the register value may be correct but still alarm may be present.
Not a working CB:This indicate clock is having hardware fault
> start shell user root Password: root@:/var/home/labroot # /usr/sbin/spc 0 0 0 1 Read at register address 0x0000 returns 0xff --> Not an expected register value for the CB. root@:/var/home/labroot # /usr/sbin/spc 1 0 0 1 Read at register address 0x0000 returns 0xff --> Not an expected register value for the CB.
Working CB:
> start shell user root Password: root@:/var/home/labroot # /usr/sbin/spc 0 0 0 1 Read at register address 0x0000 returns 0xbd --> Expected register value for the proper working CB. root@:/var/home/labroot # /usr/sbin/spc 1 0 0 1 Read at register address 0x0000 returns 0xb8 --> Expected register value for the proper working CB.
Step 2:-
Enter into root shell mode:
botanix-re0> start shell user root
Password:
Issue the command below root shell mode.
botanix-re0/var/home/full # cbc -a | grep DPC_CLK_DETECT
0x0050: DPC_CLK_DETECT: 0x00c28f08
Convert the hex register value received from above command into binary using third-party online tool. You can easily find the hex-to-binary tools on the Internet.
The 26th bit of converted Binary number from hex conversion is used for verifying clock failure. If this digit is ‘1’ (as highlighted ) then we can conclude that clock is functioning correctly. If it is ‘0’ then it indicates loss of clock signal.
Ex. Bad Clock:-
0x00c28f08 ---Hex To Binary---> 00000000110000101000111100001000 ---> Bad Clock
Ex. Good Clock:-
botanix-re1/var/home/full # cbc -a | grep DPC_CLK_DETECT
0x0050: DPC_CLK_DETECT: 0x04c08c08
0x04c08c08 ---Hex To Binary---> 00000100110000001000110000001000 ---> Good Clock
As a temporary workaround, perform a re-seat of CB to check if it restore the clock value if not, then it is a hardware issue. Hence, the card may need to be replaced.
2024-05-16 : Article Created
2025-10-02 : Added SRX5400 to the Categories.