Cisco Catalyst 4500 Series Software Configuration Manual page 420

How to Perform the ISSU Process
Prerequisites
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Note
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Perform the following steps at the active supervisor engine:
Command or Action
Step 1
Switch> enable
Step 2
Switch# issu loadversion
active-image-new [standby-slot]
standby-image-new [forced]
Catalyst 4500 Series Switch, Cisco IOS Software Configuration Guide - Cisco IOS XE 3.9.xE and IOS 15.2(5)Ex
8-22
Ensure that the new version of Cisco IOS XE software image is already present in the file system of
both the active and standby supervisor engines. Also ensure that appropriate boot parameters
(BOOT string and config-register) are set for the active and standby supervisor engines.
auto-boot must be enabled for ISSU to succeed.
Optionally, perform additional tests and commands to determine the current state of peers and
interfaces for later comparison.
Ensure the system (both active and standby supervisor engines) is in SSO redundancy mode. If the
system is in RPR mode, you can still upgrade the system using the ISSU CLI commands, but the
system will experience extended packet loss during the upgrade.'
Refer to the Stateful Switchover document for more details on how to configure SSO mode on
supervisor engines.
For ISSU to function, the IOS XE file names on the active and standby supervisor engines must
match.
[
active-slot]
Chapter 8 Configuring the Cisco IOS XE In Service Software Upgrade Process
Purpose
Enables privileged EXEC mode.
Enter your password if prompted.
Starts the ISSU process and (optionally) overrides the
automatic rollback when the new Cisco IOS XE software
version is detected to be incompatible.
It may take several minutes after entering the issu
loadversion command for Cisco IOS XE software to load
onto the standby supervisor engine and for the standby
supervisor engine to transition to SSO mode. This causes
the standby supervisor engine to reload with the new
software image.
If you use the forced option, the standby supervisor engine
is booted with the new software image. After the software
image is loaded on the standby supervisor engine, if the
software image is incompatible, the system is forced to the
RPR mode. Otherwise the system will continue in the SSO
mode.