Cisco Catalyst 4500 Series, Software Configuration Manual

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Catalyst 4500 Series Switch, Cisco IOS Software Configuration Guide - Cisco IOS XE 3.9.0E and IOS 15.2(5)E
Chapter 7 Configuring the Cisco IOS In-Service Software Upgrade Process
About ISSU
Changeversion Deployment Scenario
The typical issu changeversion command usage scenario is for experienced users with a large installed
base. These users typically validate a new image using a topology and configuration similar to their
production network. The validation process should be done using both the existing multi-command
process and the new
issu changeversion command process. Once users certify an IOS software image
and want to roll it out broadly, they can use the single command process to perform an efficient upgrade
of their network.
Aborting an In-Progress Changeversion Procedure
The issu changeversion command functionality is designed to perform an ISSU software upgrade
without user intervention. However, status messages are displayed to the console as the upgrade
transitions through the various states. If any anomalies are noticed during the automatic upgrade,
perhaps with peers or other parts of the network, you can use the
issu abortversion command to
manually abort the upgrade at any point in the process prior to the commitversion operation.
Guidelines for Performing ISSU
Be aware of the following guidelines while performing the ISSU process:
• Even with ISSU, it is recommended that upgrades be performed during a maintenance window.
•
The new features should not be enabled (if they require change of configuration) during the ISSU
process.
Note
Enabling them will cause the system to enter RPR mode because commands are only supported
on the new version.
•
In a downgrade scenario, if any feature is not available in the downgrade revision of the Cisco IOS
software handle, that feature should be disabled prior to initiating the ISSU process.
Versioning Capability in Cisco IOS Software to Support ISSU
Before the introduction of ISSU, the SSO mode of operation required each supervisor engine to be
running the same versions of Cisco IOS software.
Note
The operating mode of the system in a redundant HA configuration is determined by exchanging version
strings when the standby supervisor engine registers with the active supervisor engine.
The system entered SSO mode only if the versions running on the both supervisor engines were the same.
If not, the redundancy mode changes to RPR. With ISSU capability, the implementation allows two
different but compatible release levels of Cisco IOS images to interoperate in SSO mode and enables
software upgrades while packet forwarding continues. Version checking done before ISSU capability
was introduced is no longer sufficient to allow the system to determine the operating mode.