Cisco Cisco IOS Software Release 12.2(25)S

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The FHRP—SSO Aware HSRP feature alters the behavior of Hot Standby Router Protocol (HSRP) when 
a router with redundant Route Processors (RPs) is configured for Stateful Switchover (SSO) redundancy 
mode. One RP is active, and the other RP is standby. SSO enables the standby RP to take over if the 
active RP fails.

With this feature, HSRP SSO information is synchronized to the standby RP, allowing traffic that is sent 
using the HSRP virtual IP address to be continuously forwarded during a switchover without a loss of 
data or a path change. Additionally, if both RPs fail on the active HSRP router, then the standby HSRP 
router takes over as the active HSRP router.

The feature is enabled by default when the redundancy mode is SSO.

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12.2(25)S

This feature was introduced.

12.2(27)SBC

This feature was integrated into Cisco IOS Release 12.2(27)SBC.