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JUNOSe 11.1.x Service Availability Configuration Guide
When the primary SRP module has verified that all line modules are up, the redundant
SRP module takes over control of the router by becoming the active SRP module.
The primary, and formerly active, SRP module reboots to the armed release and
serves as the standby SRP module.
All applications on the newly active SRP module are restarted. Each application
reconstructs itself from the mirrored data, restoring its state and configuration as it
was before the switchover. Forwarding through the fabric is interrupted for about 1
second on the E120 and E320 routers and about 4 seconds on the ERX1440 router.
The SRP switchover restarts the routing protocols and triggers a graceful restart
because the routes need to be recomputed. This recalculation can take up to 90
seconds. Data continues to be forwarded through routes that were learned before
the upgrade of the line module control planes.
Line Module Forwarding Plane Upgrade
While the applications on the SRP module and the line modules reconstruct
themselves, they also begin to build up the new state for the forwarding subsystem.
All applications on the line module signal the system when they are ready to start
the forwarding upgrade.
Because upgrading the forwarding plane affects forwarding through the chassis for
up to 30 seconds on the E120 and E320 routers and about 50 seconds on the
ERX1440 router, unified ISSU does not proceed until the routing protocols have
signaled that route reconvergence has completed. Unified ISSU then instructs all line
modules to simultaneously upgrade their forwarding subsystems.
The line modules then perform the following steps:
1.
2.
3.
4.
5.
Related Topics
70
Unified ISSU Upgrade Phase Overview
Halt forwarding through the line modules. Although any links to external devices
remain up, incoming data is dropped.
Update any changed programmable hardware devices.
Update the forwarding subsystem with the new release and upgraded
configuration data.
Update the routing tables with the reconverged routes.
Resume forwarding.
Unified ISSU Phases Overview on page 63
Halt of Unified ISSU During Upgrade Phase Overview on page 100
Halting Unified ISSU During Upgrade Phase on page 100
issu start
show issu
halt
reload
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