# Activating High Availability

The line module can operate in one of the two redundancy modes—stateless switchover and high availability. When you activate high availability, the router uses mirroring to keep the configuration and state of the standby line module coordinated with the configuration and state of the active line module.

To activate high availability:

1. From Global Configuration mode, launch Redundancy Configuration mode.
   host1(config)#redundancy
2. In Redundancy Configuration mode, configure high availability as the redundancy mode and specify the line module pair (primary and secondary) for stateful switchover.
   host1(config-redundancy)#mode high-availability slot 11 16

   In this example, the line module that resides in slot 11 is assigned as the primary module and the line module installed in slot 16 is assigned as the standby or secondary module.

   A warning message is displayed prompting you to confirm (enter y for yes, n for no) whether you want to proceed with the reloading of the secondary line module in the high availability pair. If you enter yes, the line module pair is set for stateful switchover after a reload operation is completed on the secondary line module. If you enter no, the high availability setting is not saved on the line module pair.

   | Note: You can specify only two pairs of line modules for high availability operation. If you attempt to configure high availability for more than two pairs of line modules, an error message states that the maximum number of line-module high availability pairs are already configured on the router and the setting is not saved.

#### Related Documentation

- Guidelines for Activating High Availability
- Stateful Line Module Switchover Modes
- Application Support for Stateful Line Module Switchover
- line-card switch
- mode
- show redundancy history
- show redundancy line-card