Cisco Cisco IOS Software Release 12.2(20)S

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Development of the Stateful Switchover (SSO) feature is an incremental step within an overall program 
to improve the availability of networks constructed with Cisco IOS routers. 

is particularly useful at the network edgeSSO provides protection for network edge devices with dual 
Route Processors (RPs) that represent a single point of failure in the network design, and where an 
outage might result in loss of service for customers.

SSO has many benefits. Because the SSO feature maintains stateful protocol and application 
information, user session information is maintained during a switchover, and line cards continue to 
forward network traffic with no loss of sessions, providing improved network availability. SSO provides 
a faster switchover relative to HSA, RPR, and RPR+ by fully initializing and fully configuring the 
standby RP, and by synchronizing state information, which can reduce the time required for routing 
protocols to converge. Network stability may be improved with the reduction in the number of route flaps 
had been created when routers in the network failed and lost their routing tables.

This document describes the Stateful Switchover (SSO) feature in Cisco IOS software.

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, use the 

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.