# Understanding 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:

- 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

## 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).

You can also disable automatic switchover on individual slots. For more information, see Configuring Line Module Redundancy.

Table 3: Commands That Can Cause Automatic Switchover

Command | Reason for Automatic Switchover
--- | ---
slot disable primary-line-module-slot | The command disables the primary line module but not the primary I/O module or IOAs.
reload slot primary-line-module-slot | The command is equivalent to pushing the reset button on the primary line module.

#### Related Documentation

- Line Module Redundancy Overview
- Understanding Reversion After Switchover
- Configuring Line Module Redundancy
- Managing Line Module Redundancy