H3C Technologies H3C S7500E Series Switches - Manual (Page 208)

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2) Receivers send join messages to the nearest RP to join in the RPT rooted as this RP. In this
example, Receiver joins the RPT rooted at RP 2.
3) RPs share the registered multicast information by means of SA messages. In this example, RP 1
creates an SA message and sends it to RP 2, with the multicast data from Source encapsulated in
the SA message. When the SA message reaches RP 2, RP 2 decapsulates the message.
4) Receivers receive the multicast data along the RPT and directly join the SPT rooted at the
multicast source. In this example, RP 2 forwards the multicast data down the RPT. When
Receiver receives the multicast data from Source, it directly joins the SPT rooted at Source.
The significance of Anycast RP is as follows:
z Optimal RP path: A multicast source registers with the nearest RP so that an SPT with the optimal
path is built; a receiver joins the nearest RP so that an RPT with the optimal path is built.
z Load balancing between RPs: Each RP just needs to maintain part of the source/group
information within the PIM-SM domain and forward part of the multicast data, thus achieving load
balancing between different RPs.
z Redundancy backup between RPs: When an RP fails, the multicast source previously registered
on it or the receivers previous joined it will register with or join another nearest RP, thus achieving
redundancy backup between RPs.
z Be sure to configure a 32-bit subnet mask (255.255.255.255) for the Anycast RP address, namely
configure the Anycast RP address into a host address.
z An MSDP peer address must be different from the Anycast RP address.
Multi-Instance MSDP
MSDP peering relationship can be built between multicast-enabled interfaces that belong to the same
instance. Through exchanges of SA messages between MSDP peers, the MSDP mechanism makes
VPN multicast transmission between different PIM-SM domains possible.
A multicast router running multiple MSDP instances maintains an independent set of MSDP
mechanism for each instance it supports, including SA cache, peering connection, timers, sending
cache, and cache for exchanging information with PIM, while one instance is isolated from another;
therefore, interoperability between MSDP and PIM-SM is available only within the same instance.
Protocols and Standards
MSDP is documented in the following specifications:
z RFC 3618: Multicast Source Discovery Protocol (MSDP)
z RFC 3446: Anycast Rendezvous Point (RP) mechanism using Protocol Independent Multicast
(PIM) and Multicast Source Discovery Protocol (MSDP)