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. To use this feature, you must also install a redundancy midplane and a redundancy I/O module. For a detailed explanation of how the system provides redundancy for line modules and procedures for installing the modules, see the ERX Installation and User Guide.

The process by which the system switches to the spare line module is called switchover or failover. During switchover, the line, circuit, and IP interfaces on the I/O module 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 system 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.

Automatic Switchover

Provided you have not issued the redundancy lockout command for the primary line module, the system switches over to the spare line module automatically if it detects any of the following failures on the primary
line module:

• Power-on self-test (POST) failure
• Software-detected unrecoverable error
• Software watchdog timer expiration
• Primary line module failure to respond to keepalive polling from the SRP module
• Removal, disabling, or reloading of the primary line module
• Missing or disabled primary line modules when the system reboots
• Resetting the primary line module using the concealed push button

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 5-6).

You can also disable automatic switchover on individual slots. See Configuring Line Module Redundancy, later in this chapter.

Table 5-6 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.
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. If the system 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 system does not automatically revert to the primary module after switchover; however, you can configure it to do so. (See Configuring Line Module Redundancy, later in this chapter.) 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 system
as follows:

• Disable automatic switchover on a slot.
• Enable automatic reversion after switchover.

    redundancy lockout

• Use to prevent the system from switching automatically to a spare line module if the primary module in the specified slot fails.
• The redundancy force-failover command overrides the redundancy lockout command.
• Example

host1(config)#redundancy lockout 5 

• Use the no version to restart redundancy protection for the slot.

    redundancy revertive

• Use to enable the system to revert from all spare line modules to the associated primary line modules automatically.
• Reversion takes place when the primary line module is once again available unless you specify a time of day. In that case, reversion takes place only when the primary module is available and after the specified time.
• Example

host1(config)#redundancy revertive 23:00:00 

• Use the no version to disable automatic reversion.

Managing Line Module Redundancy

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

• Force switchover manually.
• Force reversion manually.

    redundancy force-failover

• Use to force the system to switch from the primary line module in the specified slot to the spare line module.
• The command causes a single switchover. When you reboot, the system will revert to the configured setting for this slot.
• The redundancy force-failover command overrides the redundancy lockout command.
• Example

host1#redundancy force-failover 5 

• There is no no version.

    redundancy revert

• Use to force the system to revert to the primary line module in the specified slot.
• The system acts on this command immediately unless you specify a time or a time and date that the action is to take place.
• The command causes a single reversion. When you reboot, the system uses the configured setting for this slot.
• Example

host1#redundancy revert 4 23:00:00 5 September 200X

• There is no no version.

Monitoring Line Module Redundancy

You can use show commands to monitor the status of redundancy groups and line modules.

    show environment

• Use to display information about the hardware installed for redundancy.
• See ERX System Basics Configuration Guide, Chapter 4, Managing the System, for details and examples.

    show hardware

• Use to display detailed information about the line modules and SRP modules.
• See Monitoring Modules, later in this chapter, for details and examples.

    show redundancy

• Use to display the configuration for line module redundancy.
• Field descriptions

• slot - slot in which the line module resides
• hardware role - function of the line module: primary or spare
• redundancy midplane type - identifier for the type of midplane
• redundancy midplane rev - hardware revision number of the redundancy midplane
• lockout config - status of redundancy on this line module

• protected - line module redundancy is enabled
• locked out - line module redundancy is disabled

• backed up by slot - slot that contains the line module that is a spare for this primary line module
• sparing for slot - slot that contains the primary line module for which this line module is a spare

• Example

In the following example, the user issues a show redundancy command, then a force failover command. Finally, the user issues another show redundancy command. The two displays show how the states of the primary and spare line modules change.

host1#show redundancy

  automatic reverting is off

       hardware     redundancy midplane    lockout     backed up     sparing

slot     role          type    rev          config      by slot      for slot

----   --------     -------------------     ------     ---------     --------

 2       ---           ---     ---            ---         ---          ---

 6       ---           ---     ---            ---         ---          ---

 8      spare           6       0             ---         ---          ---

 9      primary         6       0          protected      ---          ---

host1#redundancy force-failover 9

host1#show redundancy

  automatic reverting is off

       hardware     redundancy midplane    lockout     backed up     sparing

slot     role          ID      rev          config      by slot      for slot

----   --------     -------------------     ------     ---------     --------

 2       ---           ---     ---            ---         ---          ---

 6       ---           ---     ---            ---         ---          ---

 8      spare           6       0             ---         ---           9

 9      primary         6       0          protected       8           ---

    show version

• Use to display information about each module in the system.
• See ERX System Basics Configuration Guide, Chapter 4, Managing the System, for details and examples.