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
.