Vrf-Aware Msdp; Multicast Nonstop Forwarding - Cisco XR12000 Series Configuration Manual

Multicast Nonstop Forwarding

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.

VRF-aware MSDP

VRF (VPN Routing and Forwarding) -aware MSDP enables MSDP to function in the VRF context. This in
turn, helps the user to locate the PIM (protocol Independent Multicast) RP on the Provider Edge and use
MSDP for anycast-RP.
MSDP needs to be VRF-aware when:
• Anycast-RP is deployed in an MVPN (Multicast MVPN) in such a manner that one or more PIM RPs
• The PIM RP is deployed in an MVPN in such a manner that it is not on a PE and when the customer
Multicast Nonstop Forwarding
The Cisco IOS XR Software 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.
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 information.
Nonstop forwarding is not supported for PIM bidirectional routes. If a PIM or MRIB failure (including
Note
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.
Cisco IOS XR Multicast Configuration Guide for the Cisco XR12000 Series Router, Release 5.1.x
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in the anycast-RP set are located on a PE. In such a deployment, MSDP needs to operate in the VRF
context on the PE.
multicast routing type for the MVPN is BGP and the PEs have suppress-shared-tree-join option configured.
In this scenario, there is no PE-shared tree link, so traffic may stop at the RP and it does not flow to
other MVPN sites. An MSDP peering between the PIM RP and one or more PEs resolves the issue.
Implementing Multicast Routing on Cisco IOS XR Software
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