Understanding Srp Module Redundancy - Juniper JUNOSE SOFTWARE FOR E SERIES 11.3.X - SERVICE AVAILABILITY CONFIGURATION GUIDE 2010-10-08 Configuration Manual

JunosE 11.3.x Service Availability Configuration Guide

Understanding SRP Module Redundancy

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NOTE: This section does not cover NVS cards or the behavior on systems
running high availability features such as hitless SRP switchover. For
information about managing NVS in a router that contains two SRP modules,
see Managing Flash Cards on SRP Modules in the JunosE System Basics
Configuration Guide. For information about managing high availability in a
router, see "Managing Stateful SRP Switchover" on page 35.
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 ERX7xx
models, ERX14xx models, and the ERX310 router, both SRP modules share a single SRP
I/O module located in the rear of the chassis. On the E120 and E320 routers, both SRP
modules share an SRP IOA located in the rear of the chassis.
NOTE: The ERX310 router does not support SRP module redundancy. For
this reason, any references to synchronization that may appear in command
output or system messages do not apply to the ERX310 router.
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-numbered 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 takes control without rebooting itself. For information about preventing the
redundant SRP module from taking control, see "Managing SRP Module Redundancy"
on page 21.
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 gives back 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 takes control, the following sequence of events occurs:
The original primary SRP module reboots and takes the redundant role.
1.
The redundant SRP module restarts and takes the primary role without reloading new
2.
code. (When upgrading software, you must reload the software on the redundant
SRP module. See Installing JunosE Software in the JunosE System Basics Configuration
Guide.)
All line modules reboot.
3.
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