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Router Behavior During a Unified In-Service Software Upgrade
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Copyright © 2010, Juniper Networks, Inc.
The following behaviors are characteristic of a unified in-service software upgrade.
Connections that were established before you begin the unified ISSU are maintained
across the upgrade. Any such connection that was forwarding data continues to do so
during and after the upgrade.
New connections are denied until the upgrade is completed.
Packet loss during the upgrade is limited. Bandwidth through the modules is reduced,
but the impact is minimal.
Graceful restart protocols do not time out during the unified ISSU.
The unified in-service software upgrade has a minimal effect on the control and data
planes. During the SRP module upgrade phase, forwarding through the fabric is
interrupted for about 1 second on the E120 and E320 routers and about 4 seconds on
the ERX1440 Broadband Services Router. During the line module upgrade phase,
forwarding through the chassis is interrupted for about 15 seconds on the E120 and
E320 routers and for about 50 seconds on the ERX1440 router.
Diagnostic software is not run on any modules during a unified in-service software
upgrade.
The router undergoes a cold restart if you attempt to upgrade the software to a
lower-numbered version with unified ISSU. The unified in-service software upgrade
must be to a higher-numbered release than the running release.
Additional memory is consumed during a unified in-service software upgrade. Available
memory on a line module might not be sufficient due to the module's configuration.
Unified ISSU can detect this limitation during the upgrade procedure and exit the
process, gracefully.
During the unified ISSU process, with a high availability line-module pair configured
on a router, the primary line module supports unified ISSU. In such a scenario, the
secondary line module is disabled when unified ISSU is performed and is cold booted
after the unified ISSU procedure is complete. High availability mode is reactivated after
the secondary line module comes back online, if the line module HA configuration
continues to remain enabled on the secondary module. For more information about
how the stateful line module switchover functionality behaves during a unified ISSU
process, see "Managing Stateful Line Module Switchover" on page 67.
Unified ISSU Phases Overview on page 107
Application Support for Unified ISSU on page 115
Hardware and Software Requirements Before Beginning a Unified ISSU on page 104
Upgrading Router Software with Unified ISSU on page 139
Chapter 5: Configuring a Unified In-Service Software Upgrade
103
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