# Line Module Redundancy Overview

You can install an extra line module in a group of identical line modules to provide redundancy if one of the modules fails.

The process by which the router switches to the spare line module is called switchover. Line modules can operate in one of the two redundancy modes: stateless switchover or high availability. Stateless switchover is the default redundancy mode. During stateless switchover, the line, circuit, and IP interfaces on the I/O module or one or more IOAs appear to go down temporarily. The duration of the downtime depends on the number of interfaces and the size of the routing table, because the router must reload the interface configuration and the routing table from the SRP module.

If the line module software is not compatible with the running SRP module software release, a warning message appears on the console.

| Note: This section does not cover behavior of line modules in high availability redundancy mode. For information about stateful line module switchover, seeManaging Stateful Line Module Switchover.

#### Related Documentation

- Line Module Redundancy Requirements
- Configuring Line Module Redundancy
- Managing Line Module Redundancy
- Stateful Line Module Switchover Overview
- Guidelines for Configuring Stateful Line Module Switchover