[Contents] [Prev] [Next] [Index] [Report an Error] [No Frames]

JUNOSe 9.1.x System Basics Configuration Guide > Managing Modules > Line Module Redundancy

Line Module Redundancy

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. During 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.

Module 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 ERX-310 router, which does not support line module redundancy.


ERX-7xx Models and ERX-14xx Models

To use this feature on ERX-7xx models and ERX-14xx 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 Router and E320 Router

To configure line module redundancy on the E120 router or the E320 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 spare line module only backs up a line module of the same type. For example, an ES2 4G LM spare line module backs up any ES2 4G LM, but does not back up an ES2 10G Uplink LM. The router accepts the following redundancy groups:

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

IOA Behavior When the Router Reboots

On E120 and E320 routers, 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 there is a slot that 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.

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:

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 (see Table 42).

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





 Table 42:  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.

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. It is desirable to revert to the primary module as soon as possible. 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.

Configuring Line Module Redundancy

You can modify the default redundancy operations on the router
as follows:

redundancy lockout

redundancy revertive

Managing Line Module Redundancy

When the router is running and a redundancy group is installed, you can manage the redundancy situation as follows:

redundancy force-switchover

redundancy revert

[Contents] [Prev] [Next] [Index] [Report an Error] [No Frames]