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Unified ISSU Phases Overview
The JUNOSe software includes software modules that
operate the following hardware components:
- SRP module
- Line module control plane
- Line module forwarding plane
A unified in-service software upgrade replaces
the currently operating software on each of these components with
a higher-numbered release. The unified ISSU also upgrades or re-creates
the state and configuration data of the configured applications.
Before you begin the in-service software upgrade,
you must first prepare the router for the upgrade. See Before You Begin a Unified In-Service Software Upgrade for more information.
The in-service software upgrade takes place in
three phases:
- Initialization Phase—When you issue the issu initialize command, unified ISSU verifies whether
all prerequisites for the upgrade have been met. The router is prepared
for the upgrade. The configuration that has been mirrored to the standby
SRP module is upgraded according to the upgrade release. This phase
can last from a few minutes up to 40 minutes depending on the number
of software releases across which the router is being upgraded.
- Upgrade Phase—When you issue the issu
start command, unified ISSU again verifies whether all
prerequisites for the upgrade have been met. During this phase the
line module control plane and forwarding plane are upgraded and all
three hardware components are resynchronized.how long does this take
- Service Restoration Phase—This phase automatically
begins without user intervention when the upgrade phase has completed.
During this final phase, the router is returned to a normal, runtime
state.
The following sections describe these phases in
more detail.
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