Prior to the implementation of the Broadband High Availability Stateful Switchover feature, unplanned control plane and dataplane
failures resulted in service outages and network downtime for PPPoX sessions. Cisco HA features, including SSO, enable network
protection by providing fast recovery from such failures. The Broadband High Availability Stateful Switchover feature eliminates
a source of outages by providing for stateful switchover to a standby processor while continuing to forward traffic. SSO protects
from hardware or software faults on an active Route Processor (RP) by synchronizing protocol and state information for supported
features with a standby RP, ensuring no interruption of sessions or connections if a switchover occurs.
The SSO feature takes advantage of RP redundancy by establishing one of the RPs as the active processor, designating the other
RP as the standby processor, and then synchronizing critical state information between them. Following an initial (bulk) synchronization
between the two processors, SSO dynamically maintains RP state information between them. A switchover from the active to the
standby processor occurs when the active RP fails, when it is removed from the networking device, or when it is manually taken
down for maintenance. The standby RP then takes control and becomes the active RP, preserving the sessions and connections
for the supported features. At this time, packet forwarding continues while route convergence is completed on the newly active
RP. A critical component of SSO and Cisco HA technology is the cluster control manager (CCM) that manages session re-creation
on the standby processor. The Broadband High Availability Stateful Switchover feature allows you to configure subscriber redundancy
policies that tune the synchronization process. For more information, see the Configuring Subscriber Redundancy Policy for Broadband HA Stateful Switchover.
The Broadband High Availability Stateful Switchover feature works with the Cisco NSF and SSO HA features, to maintain PPPoX
sessions. NSF forwards network traffic and application state information so that user session information is maintained after
a switchover.
For information about High Availability and stateful switchover, see the "High Availability Overview" chapter in the
Cisco ASR 1000 Series Aggregation Services Routers Software Configuration Guide
.