Multicast Source Discovery Protocol; Vrf-Aware Msdp; Multicast Nonstop Forwarding - Cisco ASR 9000 Series Configuration Manual

Multicast Source Discovery Protocol

• VC label-based load balancing.
Multicast Source Discovery Protocol
Multicast Source Discovery Protocol (MSDP) is a mechanism to connect multiple PIM sparse-mode domains.
MSDP allows multicast sources for a group to be known to all rendezvous points (RPs) in different domains.
Each PIM-SM domain uses its own RPs and need not depend on RPs in other domains.
An RP in a PIM-SM domain has MSDP peering relationships with MSDP-enabled routers in other domains.
Each peering relationship occurs over a TCP connection, which is maintained by the underlying routing
system.
MSDP speakers exchange messages called Source Active (SA) messages. When an RP learns about a local
active source, typically through a PIM register message, the MSDP process encapsulates the register in an
SA message and forwards the information to its peers. The message contains the source and group information
for the multicast flow, as well as any encapsulated data. If a neighboring RP has local joiners for the multicast
group, the RP installs the S, G route, forwards the encapsulated data contained in the SA message, and sends
PIM joins back towards the source. This process describes how a multicast path can be built between domains.
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
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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 Layer-3 Multicast Routing on Cisco IOS XR Software