Guidelines For Performing Issu - Cisco Catalyst 4500 series Administration Manual

Chapter 5 Configuring Virtual Switching Systems
The in command option schedules an automatic ISSU upgrade to begin after a certain amount of time
has elapsed. This option specifies the number of hours and minutes (hh:mm format) that must elapse
before an upgrade will occur, with a maximum value of 99:59.
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 XE 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:
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Compatibility Matrix
ISSU requires additional information to determine compatibility between software versions. Therefore,
a compatibility matrix is defined that contains information about other IOS XE software image with
respect to the one in question.
This compatibility matrix represents the compatibility of two software versions, one running on the
active and the other on the standby supervisor engine, and to allow the system to determine the highest
operating mode it can achieve. Incompatible versions will not be able to progress to SSO operational
mode. Because SSO is a pre-requisite for a VSS, incompatibility will also lead to the loss of VSS
relationship between the supervisors engines in the two switches.
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Even with ISSU, it is recommended that upgrades be performed during a maintenance window.
As explained in Traffic and Network Protocol Disruption During ISSU in a VSS, page
on VSS may cause loss of network connectivity to both the VSS switches at some point during the
process (although not at the same time). The mitigation steps as explained in that section must be
implemented.
The new features should not be enabled (if they require change of configuration) during the ISSU
process.
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 XE software handle, that feature should be disabled prior to initiating the ISSU process.
Software Configuration Guide—Release IOS XE 3.6.0E and IOS 15.2(2)SG
In-Service Software Upgrade (ISSU) on a VSS
5-57, ISSU
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