Cisco Catalyst 4500 Series Software Configuration Manual page 408

About Performing ISSU
After a switchover (NSF/SSO, not RPR), the standby supervisor engine takes over as the new active
supervisor engine (see
Figure 8-6
Catalyst 4500 Series Switch, Cisco IOS Software Configuration Guide - Cisco IOS XE 3.9.xE and IOS 15.2(5)Ex
8-10
Chapter 8
Figure 8-6).
Switch Over to Standby Supervisor Engine
Run new version
of Cisco IOS XE
the new active
Cisco IOS XE Cisco IOS XE Cisco IOS XE
3.x.y.SG 3.x.y.SG 3.x.y.SG
Old
Active NSF/SSO NSF/SSO
Supervisor
Supervisor Switchover Switchover
Engine
Line cards
Configuring the Cisco IOS XE In Service Software Upgrade Process
Cisco IOS XE Cisco IOS XE Cisco IOS XE
3.z.y.SG 3.z.y.SG 3.z.y.SG
New
Active
Engine