Multicast Nonstop Forwarding; Multicast Configuration Submodes - Cisco XR 12000 Series Configuration Manual

Information About Implementing Multicast Routing
Although you should configure BGP or Multiprotocol BGP for optimal MSDP interdomain operation,
Note
this is not considered necessary in the Cisco IOS XR software implementation. For information about
how BGP or Multiprotocol BGP may be used with MSDP, see the MSDP RPF rules listed in the
Multicast Source Discovery Protocol (MSDP), Internet Engineering Task Force (IETF) Internet draft.

Multicast Nonstop Forwarding

The Cisco IOS XR nonstop forwarding (NSF) feature for multicast enhances high availability (HA) of
multicast packet forwarding. NSF prevents hardware or software failures on the control plane from
disrupting the forwarding of existing packet flows through the router.
How does multicast NSF work? The contents of the Multicast Forwarding Information Base (MFIB) are
frozen during a control plane failure. Subsequently, PIM attempts to recover normal protocol processing
and state before the neighboring routers time out the PIM hello neighbor adjacency for the problematic
router. This behavior prevents the NSF-capable router from being transferred to neighbors that will
otherwise detect the failure through the timed-out adjacency. Routes in MFIB are marked as stale after
entering NSF, and traffic continues to be forwarded (based on those routes) until NSF completion. On
completion, MRIB notifies MFIB and MFIB performs a mark-and-sweep to synchronize MFIB with the
current MRIB route info.
Note Nonstop forwarding is not supported for PIM bidirectional routes. If a PIM or MRIB failure (including
RP failover) happens with multicast-routing NSF enabled, PIM bidirectional routes in the MFIBs are
purged immediately and forwarding on these routes stops. Routes are reinstalled and forwarding
recommences after NSF recovery has ended. This affects only bidirectional routes. PIM-SM and
PIM-SSM routes are forwarded with NSF during the failure. This exception is designed to prevent
possible multicast routing loops from forming when the control plane is not able to participate in the
BiDir Designated Forwarder election.

Multicast Configuration Submodes

Cisco IOS XR software moves control plane CLI configurations to protocol-specific submodes to
provide mechanisms for enabling, disabling, and configuring multicast features on a large number of
interfaces.
Cisco IOS XR software allows you to issue most commands available under submodes as one single
command string from global configuration mode.
For example, the ssm command could be executed from the multicast-routing configuration submode
like this:
RP/0/0/CPU0:router(config)# multicast-routing
RP/0/0/CPU0:router(config-mcast-ipv4)# ssm range
Alternatively, you could issue the same command from global configuration mode like this:
RP/0/0/CPU0:router(config)# multicast-routing ssm range
The following multicast protocol-specific submodes are available through these configuration
submodes:
•
Multicast Configuration Guide
MCC-20
Multicast-Routing Configuration Submode, page MCC-21
Implementing Multicast Routing on Cisco IOS XR Software Cisco ASR 9000 Series Routers
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