Cisco Catalyst 4500 Series Software Configuration Manual page 365

Chapter 7 Configuring the Cisco IOS In-Service Software Upgrade Process
After a switchover (NSF or SSO, not RPR), the standby supervisor engine takes over as the new active
supervisor engine (see
Figure 7-6
Figure 7-6).
Switch Over to Standby Supervisor Engine
Cisco IOS Cisco IOS
12.x(y)S 12.x(y)S
Old
Active NSF/SSO NSF/SSO
Supervisor Switchover Switchover
Engine
Line cards
Catalyst 4500 Series Switch, Cisco IOS Software Configuration Guide - Cisco IOS XE 3.9.0E and IOS 15.2(5)E
Run new version
of Cisco IOS
on standby
Cisco IOS Cisco IOS
12.x(z)S 12.x(y)S
New
Active
Supervisor
Engine
About ISSU
7-9