Troubleshooting Tip: HA Synchronization failure due to priority value in 'modem' interface

The HA is out of sync due to configuration differences on the system.interface of the modem. Below is an example output from both the primary and secondary FortiGates.

The current primary is JJ-01 and the secondary is JJ-02

JJ-01 (global) # diagnose sys ha checksum show global system.interface modem
[name]='modem': 11325d912af10e25f6bcb92630b3f9ad
[vdom]='root': af813d778dc917407271953725916b8d
[mode]='pppoe': 632411fff2fc45f885c30ff48328f46d
[distance]='1': 2776ea2c12bd88353378e4f38ad7dbda
[priority]='0': 422564ccdae72258a309ba4b9381abaf
[status]='down': 05dacc64cf3afdf7b1749ebc31aa9d82
[type]='physical': 39d37257932bbbeb5593b348f9a9ce57
[snmp-index]='11': 5f3edb8c0ea96286b8b35c11770c8fd9

JJ-02 (global) # diagnose sys ha checksum show global system.interface modem
[name]='modem': 11325d912af10e25f6bcb92630b3f9ad
[vdom]='root': af813d778dc917407271953725916b8d
[mode]='pppoe': 632411fff2fc45f885c30ff48328f46d
[distance]='1': 2776ea2c12bd88353378e4f38ad7dbda
[status]='down': 05dacc64cf3afdf7b1749ebc31aa9d82
[type]='physical': 39d37257932bbbeb5593b348f9a9ce57
[snmp-index]='11': 5f3edb8c0ea96286b8b35c11770c8fd9

The difference is that in JJ-FW-01, the priority value is set to 0.

The configuration is as given below:

JJ-01 (global) # show system interface modem
config system interface
    edit "modem"
        set vdom "root"
        set mode pppoe
        set distance 1
        set priority 0
        set status down
        set type physical
        set snmp-index 11
    next
end

JJ-02 (global) # show system interface modem
config system interface
    edit "modem"
        set vdom "root"
        set mode pppoe
        set distance 1
        set status down
        set type physical
        set snmp-index 11
    next
end

The integer value range for the priority value is 1 to 64435.

JJ-01 (modem) # set priority
priority Enter an integer value from <1> to <65535> (default = <1>).

This configuration is a read-only setting, which means that even an admin with super_admin privileges is not allowed to configure this value. The following message will be displayed when the configuration to change the priority value is attempted.

JJ-01 (modem) # set priority 1
cannot change read-only setting.

Workaround:

Perform a failover to make JJ-02 the primary. Reboot JJ-01 which was previously the primary, and allow it to reconnect to HA. This will restore the priority settings on the system interface modem to the default value of 1. The HA will remain in sync if JJ-01 is set to be the primary again.