# Understanding 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.) Before reversion can take place, the primary line module must complete the POST diagnostics.

#### Related Documentation

- Understanding Automatic Switchover
- Line Module Redundancy Overview