Cisco Catalyst 4500 Series Software Configuration Manual page 364

About ISSU
After you have copied the Cisco IOS software to both file systems, load the new version of Cisco IOS
software onto the standby supervisor engine (see
Without the ISSU feature, you cannot have SSO or NSF functioning between the active and standby
Note
supervisor engines when they are running two different versions of Cisco IOS image.
Figure 7-5
Catalyst 4500 Series Switch, Cisco IOS Software Configuration Guide - Cisco IOS XE 3.9.0E and IOS 15.2(5)E
7-8
Load New Version of Cisco IOS Software on the Standby Supervisor Engine
Load new version
Cisco IOS Cisco IOS
12.x(y)S 12.x(y)S
Cisco IOS Cisco IOS
12.x(z)S 12.x(z)S
Active
NSF/SSO
Supervisor Supervisor
Engine
Line cards
Chapter 7 Configuring the Cisco IOS In-Service Software Upgrade Process
Figure 7-5).
of Cisco IOS
on standby
Cisco IOS Cisco IOS
12.x(z)S 12.x(y)S
Standby
Engine