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JunosE 11.3.x Service Availability Configuration Guide
Unified ISSU Overview
102
Unexpected T3 Behavior During Unified ISSU on page 135
Unavailability of TACACS+ Services During Unified ISSU on page 135
Interruption in Traffic Forwarding for Layer 3 Routing Protocols During Unified
ISSU on page 135
Recommended Settings for Routing Protocol Timers During Unified ISSU on page 138
Upgrading Router Software with Unified ISSU on page 139
Halt of Unified ISSU During Initialization Phase Overview on page 142
Halting Unified ISSU During Initialization Phase on page 142
Halt of Unified ISSU During Upgrade Phase Overview on page 143
Halting Unified ISSU During Upgrade Phase on page 143
Monitoring the Status of the Router During Unified ISSU on page 144
In software releases numbered lower than Release 6.0, all line modules are reloaded
when an SRP switchover occurs. This reload disconnects user sessions and disrupts
forwarding through the chassis. Stateful SRP switchover was introduced in JunosE Release
6.0 to minimize the impact to the router of a stateful switchover from the active SRP
module to the standby SRP module. Stateful SRP switchover (high availability) maintains
user sessions during the switchover and data forwarding through the router continues
to flow with little impact, thus improving the overall availability of the router.
The unified in-service software upgrade (unified ISSU) feature further extends router
availability. Unified ISSU enables you to upgrade the router to a higher-numbered software
release without disconnecting user sessions or disrupting forwarding through the chassis.
A conventional software upgrade—one that does not use the unified ISSU process—causes
a router-wide outage for all users. Only static configurations (stored on the flash card)
are maintained across the upgrade; all dynamic configurations are lost. A conventional
upgrade takes 30-40 minutes to complete, with additional time required to bring all
users back online.
When you perform a unified in-service software upgrade on a router that has one or more
modules that do not support unified ISSU, these modules alone are upgraded by means
of the legacy, conventional upgrade process. The unsupported modules undergo a cold
reboot at the beginning of the unified ISSU process, and are held down until the in-service
software upgrade is completed. Connections that pass through the unsupported modules
are lost. The interfaces on these modules pass into a down state, which causes the
physical layer and link layer to go down during the unified in-service software upgrade
for those modules.
Applications that do not support unified ISSU applications cannot maintain state and
configuration with minimal traffic loss across the upgrade to a higher-numbered release.
When you attempt a unified in-service software upgrade on a router on which a unified
ISSU-challenged application is configured, the unified in-service software upgrade cannot
proceed. You must unconfigure the unified ISSU-challenged application to successfully
perform the unified ISSU.
Copyright © 2010, Juniper Networks, Inc.
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