Cisco Catalyst 4500 Series Software Configuration Manual page 287

Chapter 5 Configuring Virtual Switching Systems
Figure 5-11 States of VSS Active and Standby during Command Execution
During the ISSU process, several show commands are available to evaluate the success of each command
before proceeding to the next step.
ISSU using the Single Command Sequence (issu changeversion)
The use of multiple ISSU commands dictates an additional level of care to ensure no service disruption.
However, in some scenarios, this upgrade procedure might be cumbersome and of minimal value. A
typical example is during a network upgrade that involves performing an ISSU upgrade on a large
number of Catalyst 4500 switches. In these cases, we recommend that you first perform the manual (four
command) ISSU upgrade procedure on one VSS (possibly in a lab environment) to verify successful
upgrade. Then, use the single issu changeversion procedure to perform an automatic ISSU on the rest
of the Catalyst 4500 switches in the network.
The issu changeversion command launches a single-step complete ISSU upgrade cycle. It performs the
logic for all four of the standard commands (issu loadversion, issu runversion, issu acceptversion, and
issu commitversion) without user intervention, streamlining the upgrade through a single CLI step.
Additionally, issu changeversion allows the upgrade process to be scheduled for a future time. This
enables you to stage a number of systems to perform upgrades sequentially when a potential disruption
would be least harmful.
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Catalyst 4500 Series Switch, Cisco IOS Software Configuration Guide - Cisco IOS XE 3.9.xE and IOS 15.2(5)Ex
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In-Service Software Upgrade (ISSU) on a VSS
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Chassis running
the pre-upgrade
version
Chassis
undergoing
reboot
Chassis running
the post-upgrade
image
SSO Active
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Switch.
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