Cisco Cisco IOS Software Release 12.0(22)S

This document describes the Multicast Subsecond Convergence feature in Cisco IOS Release 12.0(22)S 
and includes the following sections:

The Multicast Subsecond Convergence feature in Cisco IOS Release 12.0(22)S comprises a 
comprehensive set of features and protocol enhancements that provide for improved scalability and 
convergence in multicast-based services. This feature set provides for the ability to scale to larger 
services levels and to recover multicast forwarding after service failure in subsecond time frames.

Multicast subsecond convergence allows you to send Protocol Independent Multicast (PIM) router-query 
messages (PIM hellos) every few milliseconds. In previous releases, you could send the PIM hellos every 
few seconds. By enabling a router to send PIM hello messages more often, this feature allows the router 
to discover unresponsive neighbors more quickly. As a result, the router can implement failover or 
recovery procedures more efficiently.

The Multicast Subsecond Convergence feature set enhances both enterprise and service provider 
network backbones by providing almost instantaneous recovery of multicast paths after unicast routing 
recovery. Forwarding performance is unaffected by this new feature and is comparable to previous 
releases of Cisco 12.0 S software.

12.0(22)S

This feature was introduced.