Automatic Switchover; Limitations Of Automatic Switchover; Reversion After Switchover; Chapter 2 Managing Module Redundancy - Juniper SERVICE AVAILABILITY - CONFIGURATION GUIDE V 11.1.X Configuration Manual

module redundancy actions, issue the redundancy lockout command for the primary
line module slot before issuing the adapter disable or adapter enable commands.

Automatic Switchover

Provided you have not issued the redundancy lockout command for the primary
line module, the router switches over to the spare line module automatically if it
detects any of the following failures on the primary line module:

Limitations of Automatic Switchover

If automatic switchover is enabled on a slot (the default configuration) and a spare
line module is available, issuing some CLI commands for the primary line module
causes a switchover (Table 3 on page 9).
You can also disable automatic switchover on individual slots. For more information,
see "Configuring Line Module Redundancy" on page 10.

Table 3: Commands That Can Cause Automatic Switchover

Reversion After Switchover

You can install only one spare line module in the group of slots covered by the
redundancy midplane or redundancy group. If the router is using the spare line
module, no redundancy is available. Reverting to the primary module as soon as
possible is desirable. By default, the router does not automatically revert to the
primary module after switchover; however, you can configure it to do so.
(See "Configuring Line Module Redundancy" on page 10.) Before reversion can take
place, the primary line module must complete the POST diagnostics.
Power-on self-test (POST) failure
Software-detected unrecoverable error
Software watchdog timer expiration
Primary line module failure to respond to keepalive polling from the SRP module
Removal, disabling, or reloading of the primary line module
Missing or disabled primary line modules when the router reboots
Resetting the primary line module using the concealed push button
Command
slot disable primary-line-module-slot
reload slot primary-line-module-slot
Chapter 2: Managing Module Redundancy
Reason for Automatic Switchover
The command disables the primary line module
but not the primary I/O module or IOAs.
The command is equivalent to pushing the reset
button on the primary line module.
Line Module Redundancy Overview
9