SRP Module Redundancy

This section covers general issues of SRP module redundancy. For information about managing NVS in a system that contains two SRP modules, see Managing NVS Cards on SRP Modules.

The SRP module uses a 1:1 redundancy scheme. When two SRP modules are installed in the system, one acts as a primary and the second as a redundant module. Both SRP modules share a single SRP I/O module located in the rear of the chassis.

After you install two SRP modules, the modules negotiate for the primary role. A number of factors determine which module becomes the primary; however, preference is given to the module in the lower slot. The SRP modules record their latest roles and retain them the next time you switch on the system.

With the default software settings, if the primary SRP module fails, the redundant SRP module assumes control without rebooting itself. For information about preventing the redundant SRP module from assuming control, see Managing Line Module Redundancy, earlier in this chapter.

When the redundant SRP module assumes control, the following sequence of events occurs:

1. The original primary SRP module reboots and assumes the redundant role.
2. The redundant SRP module restarts and assumes the primary role without reloading new code. (When upgrading software, you must reload the software on the redundant SRP module. See ERX Installation and User Guide, Appendix E, Installing ERX System Software.)
3. All line modules reboot.

The following actions activate the redundant SRP module:

• Failure of the primary SRP module (hardware or software)
• Pushing the recessed reset button on the primary SRP module (see Figure 5-1)
• Issuing the srp switch command

Figure 5-1 SRP module

Installing a Redundant SRP Module

You can install a redundant SRP module into a running system, provided that the redundant SRP module has a valid software release on its NVS card. Access to a software release in NVS ensures that the redundant SRP module can boot; the release need not be the same as that on the primary SRP module. To install a redundant SRP module into a running system, follow these steps:

Warning: Do not insert any metal object, such as a screwdriver, or place your hand into an open slot or the backplane when the system is on. Remove jewelry (including rings, necklaces, and watches) before working on equipment that is connected to power lines. These actions prevent electric shock and serious burns.

Caution: When handling modules, use an antistatic wrist strap connected to the systems's ESD grounding jack, and hold modules by their edges. Do not touch the components, pins, leads, or solder connections. These actions help to protect modules from damage by electrostatic discharge.

1. Install the redundant SRP module into the open SRP slot (slot 6 or 7 for the ERX-1400 series; slot 0 or 1 for the ERX-700 series).

For detailed information about installing the SRP module, see the ERX Installation and User Guide.

2. Wait for the redundant SRP module to boot, initialize, and reach the standby state.

When the module is in standby state, the REDUNDANT LED is on and the ONLINE LED is off. If you issue the show version command, the state field for the slot that contains the redundant SRP module should be standby.

3. Synchronize the NVS file system of the redundant SRP module to that of the primary SRP module.
4. Reboot the redundant SRP module.

    reload slot

• Use to reboot a selected slot on the router.
• Example

host1#reload slot 7

• There is no no version.

    synchronize

• Use to force the file system of the redundant SRP module to synchronize with the NVS file system of the primary SRP module.
• If you synchronize the redundant SRP module with the primary SRP module and the redundant module is armed with a release different than the one it is currently running, the redundant SRP module is automatically rebooted to load the armed release.
• Example

host1#synchronize

• There is no no version.

Managing SRP Module Redundancy

You can prevent the redundant SRP module from taking over when:

• The primary SRP module experiences a software failure.
• You push the reset button on the primary SRP module.

Note: If you do not configure this option, when troubleshooting an SRP module, disconnect the other SRP module from the system. This action prevents the redundant SRP module from taking over if you push the reset button on the primary SRP module.

To configure this option:

1. Issue the disable-switch-on-error command.
2. Synchronize the NVS file system of the redundant SRP module to that of the primary SRP module.

Refer to the commands and guidelines in the previous section and below.

    disable-switch-on-error

• Use to prevent the redundant SRP module from taking over if the primary SRP module experiences a software failure or if you push the reset button on the primary SRP module.
• Issue the sync command immediately before you issue this command.
• If you issue the disable-switch-on-error command, and later issue the srp switch command, the redundant SRP module waits about 30 seconds before it takes over from the primary SRP module.
• Example

host1(config)#disable-switch-on-error

• Use the no version to revert to the default situation, in which the redundant SRP module takes over if the primary SRP module experiences a software failure.

    synchronize

• Use to force the NVS file system of the redundant SRP module to synchronize with the NVS file system of the primary SRP module.
• If you synchronize the redundant SRP module with the primary SRP module and the redundant module is armed with a release different than the one it is currently running, the redundant SRP module is automatically rebooted to load the armed release.
• Example

host1#synchronize

• There is no no version.

Switching to the Redundant SRP Module

To switch immediately from the primary SRP module to the redundant SRP module, issue the srp switch command. You can configure the system to prompt you if the modules are in a state that could lead to loss of configuration data or NVS corruption.

    srp switch

• Use to switch from the primary SRP module to the redundant SRP module.
• If you specify the force keyword, the procedure will fail if the SRP modules are in certain states, such as during a synchronization. In these cases, the system will display a message that indicates that the procedure cannot currently be performed and the reason why. However, if the SRP modules are in other states that could lead to a loss of configuration data or an NVS corruption, the system displays a message that explains the state of the SRP modules, and asks you to confirm (enter yes or no) whether you want to proceed.
• If you do not specify the force keyword, the procedure will fail if the SRP modules are in any state that could lead to a loss of configuration data or an NVS corruption, and the system will display a message that explains why the command failed.
• When you issue this command, the system prompts you for a confirmation before the command takes effect.
• If you issue the disable-switch-on-error command, and later issue the srp switch command, the redundant SRP module waits about 30 seconds before it takes over from the primary SRP module.
• If the system does not contain a redundant SRP module, this command has no effect.
• Example

host1#srp switch

host1#srp switch force

• There is no no version.

Upgrading Software on a Redundant SRP Module

For information about upgrading software on SRP modules, see ERX Installation and User Guide, Appendix E, Installing ERX System Software

Monitoring the Status LEDs

You can determine the redundancy state of line modules and SRP modules by examining their status LEDs. See Table 5-4 for a description of the LEDs functions. In addition, if you issue the show version command, the state field for the slot that contains the redundant SRP module should be standby.

Table 5-4 Function of the online and redundant LEDs 

ONLINE LED	REDUNDANT LED	State of the Module
Off	Off	Module is booting or is an inactive primary line module.
On	Off	Module is active, but no redundant module is available.
Off	On	Module is in standby state.
On	On	Module is active, and a redundant module is available.