678 CHAPTER 48: MSDP CONFIGURATION
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Usually an Anycast RP address is configured on a logic interface, like a loopback
interface.
Figure 202 Typical network diagram of Anycast RP
The work process of Anycast RP is as follows:
1 The multicast source registers with the nearest RP. In this example, Source registers
with RP 1, with its multicast data encapsulated in the register message. When the
register message arrives to RP 1, RP 1 decapsulates the message.
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:
■ 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.
■ 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.
■ 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.
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CAUTION:
■ 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.
■ An MSDP peer address must be different from the Anycast RP address.
SA message
Source Receiver
Router A
Router B
RP 1 RP 2
PIM-SM
MSDP peers
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