Issu Process - Cisco Catalyst 4500 Series Configuration Manual

About Performing ISSU

ISSU Process

The ISSU process allows you to perform a Cisco IOS XE software upgrade or downgrade while the
system continues to forward packets. (For an illustration of the commands used during the ISSU process,
refer to
infrastructure—Cisco NSF with SSO and hardware redundancy—and eliminates downtime associated
with software upgrades by allowing changes while the system remains in service (see
SSO and NSF mode support configuration and runtime state synchronization from the active to the
standby supervisor engine. For this process, the IOS XE software image on both the active and the
standby supervisor engines must be the same. When images on active and standby supervisor engines
are different, ISSU allows the two supervisor engines to be kept in synchronization even when these two
versions of Cisco IOS XE support different sets of features and commands.
Figure 6-3
Control
plane
Data
plane
Software Configuration Guide—Release IOS XE 3.3.0SG and IOS 15.1(1)SG
6-6
Figure 6-8.) Cisco IOS XE ISSU takes advantage of the Cisco IOS XE high availability
High Availability Features and Hardware Redundancy in the ISSU Process
Active
Supervisor NSF/SSO
Engine
Line cards
Chapter 6 Configuring the Cisco IOS XE In Service Software Upgrade Process
Management Management
Standby
plane plane
Supervisor
Engine
Figure 6-3).
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