# Line Module Redundancy Requirements

The requirements for line module redundancy depend on the type of router that you have.

| Note: The information in this section does not apply to the ERX310 Broadband Services Router, which does not support line module redundancy.

## ERX7xx Models and ERX14xx Models

To use this feature on ERX7xx models and ERX14xx models, you must also install a redundancy midplane and a redundancy I/O module. For a detailed explanation of how the router provides redundancy for line modules and procedures for installing the modules, see the ERX Hardware Guide.

## E120 and E320 Routers

To configure line module redundancy on the E120 or E320 Broadband Services router, you must also install an ES2-S1 Redund IOA in either slot 0 or slot 11. The ES2-S1 Redund IOA is a full-height IOA. For a detailed explanation of how the router provides redundancy for line modules and procedures for installing the modules, see the E120 and E320 Hardware Guide.

On E120 and E320 routers, each side of the chassis is treated as a redundancy group. The lowest numbered slot for each side acts as the spare line module, providing backup functionality when an ES2-S1 Redund IOA is located directly behind it. When the line module does not contain an ES2-S1 Redund IOA, it is considered a primary line module.

The router accepts the following redundancy groups:

- ES2 4G LM as backup and ES2 4G LM as primary
- ES2 10G Uplink LM and ES2 10G Uplink LM as primary
- ES2 10G LM as backup and ES2 10G LM
- ES2 10G ADV LM as backup and ES2 10G ADV LM as primary
- ES2 10G ADV LM as backup and ES2 10G LM as primary

Also, you cannot configure stateless switchover redundancy for the ES2-S1 Service IOA.

In a redundancy group of line modules, if an ES2 10G LM functions as the primary line module and an ES2 10G ADV LM operates as the standby module, a stateless switchover happens from the primary to the secondary line module when the primary line module has encountered a failure. After the switchover occurs, the ES2 10G LM starts functioning as the standby module and the ES2 10G ADV LM becomes the primary module.

In such a scenario, you cannot use the redundancy revert command in Global Configuration mode or redundancy revertive command in Privileged Exec mode to revert the ES2 10G LM as the primary module.

We recommend that you lock out all the ES2 10G ADV LMs in the redundancy group to prevent a stateless switchover from ES2 10G LMs to ES2 10G ADV LMs. Using ES2 10G ADV LMs as the backup modules for ES2 10 ADV LMs that operate as primary modules is undefined.

### IOA Behavior When the Router Reboots

On E120 and E320 routers, stateless switchover is based on the combined states of the line module and the IOAs that are installed in the affected slot.

When the router reboots and the formerly configured primary line module is not present, or is present and fails diagnostics, it switches to a spare line module and takes inventory of the IOAs. If the IOA is present and new, the router reverts back to the primary line module so that the spare line module can service other active primary line modules.

When the router reboots and a slot contains a line module and one active and one inactive IOA, the inactive IOA remains in that state.

### Line Module Behavior When Disabling or Enabling IOAs

On E120 and E320 routers, a line module reboots when you issue the adapter disable or adapter enable commands for an associated IOA.

When you issue the adapter disable or adapter enable commands, the line module (primary or spare) currently associated with that IOA reboots. If the IOA is protected by a line module redundancy group, an automatic line module redundancy switchover or revert can be triggered by the line module reboot. To prevent undesired line module redundancy actions, issue the redundancy lockout command for the primary line module slot before issuing the adapter disable or adapter enable commands.

#### Related Documentation

- Line Module Redundancy Overview
- Configuring Line Module Redundancy
- Managing Line Module Redundancy
- Stateful Line Module Switchover Overview
- Stateful Line Module Switchover Platform Considerations