SRP Module Behavior

The SRP module uses a 1:1 redundancy scheme. When two SRP modules are installed in the router, one acts as a primary and the second as a redundant module. On ERX-7xx models, ERX-14xx models, and the ERX-310 router, both SRP modules share a single SRP I/O module located in the rear of the chassis. On the E120 router and the E320 router, both SRP modules share an SRP IOA 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 router.

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 SRP Module Redundancy.

On E120 and E320 routers, the switch fabric is distributed between the SFMs and the SRP modules. If the primary SRP module fails a diagnostic test on its resident slice of switch fabric, then it abdicates control to the redundant SRP module if both of the following are true:

• The standby SRP module does not indicate any error.
• The standby SRP module passes diagnostics on its attached fabric slice.

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 Installing JUNOSe 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 25 and Figure 26)
• Issuing the srp switch command
• Issuing the redundancy force-switchover command

  Figure 25: SRP Module on ERX-7xx Models and ERX-14xx Models

  

  Figure 26: SRP Module on the E120 Router and the E320 Router

  

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