Guidelines For Performing Issu - Cisco Catalyst 4500 Series Software Configuration Manual

Chapter 5 Configuring Virtual Switching Systems

Guidelines for Performing ISSU

Be aware of the following guidelines while performing the ISSU process:
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Note
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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.
The compatibility matrix represents the compatibility relationship a Cisco IOS XE software image has
with all of the other Cisco IOS XE software versions within the designated support window (for example,
all of those software versions the IOS XE software image "knows" about) and is populated and released
with every IOS XE software image. The matrix stores compatibility information between its own release
and prior releases. It is always the newest release that contains the latest information about compatibility
with existing releases in the field. The compatibility matrix is available within the Cisco IOS XE
software image and on Cisco.com so that users can determine in advance whether a successful upgrade
can be achieved using the ISSU process.
You can perform the ISSU process when the old and new Cisco IOS XE software are compatible. The
compatibility matrix information stores the compatibility among releases as follows:
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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.
Compatible—The base-level system infrastructure and all optional HA-aware subsystems are
compatible. An in-service upgrade or downgrade between these versions will succeed with minimal
service impact. The matrix entry designates the images to be compatible (C).
Base-level compatible—One or more of the optional HA-aware subsystems is not compatible. An
in-service upgrade or downgrade between these versions will succeed; however, some subsystems
will not be able to maintain state always during the transition from the old to the new version of
Cisco IOS XE. The matrix entry designates the images to be base-level compatible (B).
Incompatible—A core set of system infrastructure exists in Cisco IOS XE that must be able to
interoperate in a stateful manner for SSO to function correctly. If any of these required features or
subsystems is not interoperable, then the two versions of the Cisco IOS XE software image are
declared to be incompatible. An in-service upgrade or downgrade between these versions is not
Catalyst 4500 Series Switch, Cisco IOS Software Configuration Guide - Cisco IOS XE 3.9.xE and IOS 15.2(5)Ex
In-Service Software Upgrade (ISSU) on a VSS
5-57, ISSU
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