Manual
Cisco IOS In Service Software Upgrade Process
Information About Performing ISSU
4
Cisco IOS Release 12.2(28)SB
Information About Performing ISSU
Before you perform ISSU, you should understand the following concepts:
• ISSU Process Overview, page 4
• Stateful Switchover Overview, page 10
• NSF Overview, page 12
• Versioning Capability in Cisco IOS Software to Support ISSU, page 13
• ISSU-Capable Protocols and Applications, page 14
• SNMP Support for ISSU, page 15
• Compatibility Verification Using Cisco Feature Navigator, page 15
ISSU Process Overview
The ISSU process allows you to perform a Cisco IOS software upgrade or downgrade while the system
continues to forward packets. Cisco IOS ISSU takes advantage of the Cisco IOS high availability
infrastructure—Cisco NSF with SSO and hardware redundancy—and eliminates downtime associated
with software upgrades or version changes by allowing changes while the system remains in service (see
Figure 1). Cisco IOS software high availability features combine to lower the impact that planned
maintenance activities have on network service availability, with the results of less downtime and better
access to critical systems.
SSO mode supports configuration synchronization. When images on the active and standby RPs are
different, this feature allows the two RPs to be kept in synchronization although they may support
different sets of commands.