Multicast Redundancy
The Junos OS supports nondisruptive, graceful Routing Engine switchover and graceful restart for some routing protocols in the case of Routing Engine or routing process failure. You can configure many routing protocols to continue to forward packets during the Routing Engine switchover or routing process restart. To support graceful Routing Engine switchover, the router must have two Routing Engines installed and be configured properly. For more information about graceful Routing Engine switchover, see the Junos High Availability Configuration Guide.
Graceful restart of routing protocol processes is required for graceful switchover. By default, graceful restart is disabled and must be enabled at the [edit routing-options graceful-restart] hierarchy level.
PIM sparse mode uses a mechanism called a generation identifier to indicate the need for graceful restart. Generation identifiers are included by default in PIM hello messages, as specified in the Internet draft draft-ietf-pim-sm-v2-new-10.txt. An initial generation identifier is created by each PIM neighbor to establish device capabilities. When one of the PIM neighbors restarts, it sends a new generation identifier to its neighbors. All neighbors that support graceful restart and are connected by point-to-point links assist by sending multicast updates to the restarting neighbor.
The restart phase is completed either when the PIM state becomes stable or when the restart interval timer expires. If the neighbors do not support graceful restart or if they connect to each other using multipoint interfaces, the restarting router uses a restart interval timer to define the restart period.
Graceful restart is compatible with the use of all multicast protocols. However, only PIM benefits from this feature. The router does not forward multicast packets for protocols other than PIM during graceful restart or switchover, because all other multicast protocols must completely restart after a routing process failure.
To configure graceful restart for PIM, include the graceful-restart statement at the [edit routing-options] hierarchy level, and include the pim statement at the [edit protocols] hierarchy level:
For more information about graceful restart for PIM sparse mode, see Configuring PIM Sparse Mode Graceful Restart and the Junos Multicast over Layer 3 VPNs Feature Guide. For more information about graceful restart and other routing protocols, see the Junos OS High Availability Configuration Guide .
