Multicast Non-Stop Routing

Multicast non-stop routing (NSR) provides hitless-failover support on all platforms for IPv4 multicast features (default and non-default VRFs): PIM-DM, PIM-SM, and PIM-SSM.

If multicast NSR is enabled, the software state is kept in sync between the active and standby modules. The standby module is NSR ready when the software state of the standby and active modules are in sync. When the standby module is NSR ready, a hitless-failover does not result in a disruption to the multicast forwarding state or traffic

If Multicast NSR is not enabled, or if the standby module is not NSR ready, the software state of the standby and active modules are not in sync. In this case, after a switchover or failover occurs, the new active module enters protocol learning phase for a duration of 55 seconds. During this phase, it learns the protocol state information from its PIM neighbors and local clients. During this period, new multicast flows will not be forwarded, but the existing mutlicast flows (which existed prior to switchover or failover) are forwarded in hardware without any disruption. At the end of the period, all the existing flows are deleted from hardware and they are reprogrammed as per the newly learned state information. Multicast traffic will incur a slight disturbance until the new active module reprograms the hardware with new forwarding state information.

The following message is displayed on the console of the active and standby modules to indicate that the standby module is NSR ready:

Mcastv4 is NSR ready