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Software Configuration Guide—Release IOS XE 3.6.0E and IOS 15.2(2)SG
OL-30933-01
Chapter 5 Configuring Virtual Switching Systems
In-Service Software Upgrade (ISSU) on a VSS
• The type of the pre- and post-upgrade images must match precisely. Identical. ISSU is not supported
from a Universal_lite to a Universal image, or vice versa. ISSU is also not supported from a k9
image to a non-k9 image, or vice versa.
• VSS must be functionally in SSO mode; that is, both switches must be powered up and operational,
with one supervisor engine running as the SSO active, and the other as the SSO standby.
• The pre- and post-upgrade Cisco IOS XE software image files must both be available in the local
file systems (bootflash, SD card, or USB) of both the Active and the standby supervisor engines
before you begin the ISSU process.
Both supervisor engines should be running the pre-upgrade image, and should have booted from the
image location in the local file system. (bootflash, SD card, or USB).
Note The show version command can be used to confirm that the supervisor engine has actually
booted from the pre-upgrade image location in the local filesystem.
Note Auto-boot must be enabled in the rommon for ISSU to succeed. The config-register value
displayed in the output of show version can be used to confirm this.
• It is advisable to take measures to mitigate the effects of switch down-time. ISSU in a VSS will
result in loss of service on non-MEC links, and peers must be prepared for this. On links connected
over MECs, Nonstop Forwarding (NSF) must be configured and working properly. If you do not
have NSF enabled, see the Cisco Nonstop Forwarding document for further information on how to
enable and configure NSF.
• Autoboot is turned on and the current booted image matches the one specified in the BOOT
environmental variable. For details on how to configure and verify these, please refer to “Modifying
the Boot Field and Using the boot Command” section on page 3-27.
• The no ip routing command is not supported - both before starting the ISSU process, and at any
time during the ISSU process.
• Save the image on the same partition in both supervisor engines (e.g. if it is saved at slot0: in the
active supervisor engine it should be saved at slaveslot0:). Similarly if it is at bootflash: in the active
supervisor engine, it should be at savebootflash: in the standby supervisor engine.
About Performing ISSU
Note Do not make any hardware changes while performing ISSU.
Before you perform ISSU, you should understand the following concepts:
• Performing an ISSU Upgrade: Two Methods, page 5-58
• Guidelines for Performing ISSU, page 5-61
Performing an ISSU Upgrade: Two Methods
There are two ways to perform an ISSU upgrade:
• manually using a sequence of four commands
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