Cisco Cisco IOS Software Release 12.2(33)SRE

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The Cisco IOS In Service Software Upgrade (ISSU) process allows Cisco IOS software to be updated or 
otherwise modified while packet forwarding continues. In most networks, planned software upgrades are 
a significant cause of downtime. ISSU allows Cisco IOS software to be modified while packet 
forwarding continues, which increases network availability and reduces downtime caused by planned 
software upgrades. This document provides information about ISSU concepts and describes the steps 
taken to perform ISSU in a system. 

This document also provides information about Enhanced Fast Software Upgrade (eFSU) concepts. For 
further information about eFSU, see Enhanced Fast Software Upgrade on the Cisco 7600 Series Router, 
Release 12.2(33)SRB1. 

Your Cisco IOS software release may not support all of the features documented in this module. To reach 
links to specific feature documentation in this module and to see a list of the releases in which each feature is 
supported, refer to 

.

Use Cisco Feature Navigator to find information about platform support and Cisco IOS and Catalyst OS 
software image support. To access Cisco Feature Navigator, go to 

. An 

account on Cisco.com is not required.

 lists the release history for this feature.

Use Cisco Feature Navigator to find information about platform support and software image support. 
Cisco Feature Navigator enables you to determine which Cisco IOS and Catalyst OS software images 
support a specific software release, feature set, or platform. To access Cisco Feature Navigator, go to 

. An account on Cisco.com is not required.

 lists only the Cisco IOS software release that introduced support for a given feature in a given 

Cisco IOS software release train. Unless noted otherwise, subsequent releases of that Cisco IOS 
software release train also support that feature.