Cisco Catalyst 4500 Series Software Configuration Manual page 288

In-Service Software Upgrade (ISSU) on a VSS
After the standby supervisor engine initializes and the system reaches a terminal state (SSO), the
upgrade process is complete and the BOOT variable is permanently written with the new IOS XE
software image. Hence, a reset on any RP will keep the system booting the new software image. Console
and syslog messages will be generated to notify anyone monitoring the upgrade that the state transition
has occurred.
Similar to the normal ISSU upgrade procedure, the in-progress upgrade procedure initiated by the
issu changeversion command can be aborted with the issu abortversion command. If the system detects
any problems or detects an unhealthy system during an upgrade, the upgrade might be automatically
aborted.
When the issu runversion command is entered during the four step manual upgrade process, if any
incompatible ISSU clients exist, the upgrade process reports them and their side effects, and allows the
user to abort the upgrade. While performing a single-step upgrade process, when the process reaches the
runversion state, it will either automatically continue with the upgrade provided the base clients are
compatible, or automatically abort because of client incompatibility.
Changeversion: "quick" option
The issu changeversion command provides a "quick" option that can reduce the time required to
perform the automatic ISSU upgrade. When the quick command option is applied, the ISSU upgrade
state transition differs from that illustrated in
loadversion stage remains the same as described in the figure, but the runversion and commitversion
stages are combined. This progression skips the step in the upgrade procedure that loads the old software
version on the new standby (old active) supervisor, thereby reducing the time required for the automatic
ISSU upgrade by about a third.
Scheduled Changeversion: "in" and "at" Options
issu changeversion provides in and at command options that enable you to schedule a future automatic
ISSU upgrade.
The at command option schedules an automatic ISSU upgrade to begin at a specific time. This option
specifies an exact time (hh:mm, 24 hour format) in the next 24 hours at which the upgrade will occur.
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.
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Chapter 5 Configuring Virtual Switching Systems
Figure 5-9. With this option, the state progression upto the