Cisco Catalyst 4500 series Administration Manual page 276

In-Service Software Upgrade (ISSU) on a VSS
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.
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.
Software Configuration Guide—Release IOS XE 3.6.0E and IOS 15.2(2)SG
5-60
Chapter 5 Configuring Virtual Switching Systems
Figure 5-9. With this option, the state progression upto the
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