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CX11x, CX31x, CX710 (Earlier Than V6.03), and CX91x Series Switch Modules V100R001C10 Configuration Guide 12

The documents describe the configuration of various services supported by the CX11x&CX31x&CX91x series switch modules The description covers configuration examples and function configurations.
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Introduction to MSDP

Introduction to MSDP

This section describes the definition, purpose, and benefits of MSDP.


Multicast Source Discovery Protocol (MSDP) is an inter-domain multicast solution developed for interconnection among multiple Protocol Independent Multicast Sparse Mode (PIM-SM) domains. It is used to discover information about multicast sources in other PIM-SM domains.

MSDP can be deployed only on an IPv4 network and the intra-domain multicast routing protocol must be PIM-SM. MSDP is valid only for the Any-Source Multicast (ASM) model.


In PIM-SM mode, a source designated router (DR) registers to a rendezvous point (RP) and a receiver DR sends Join messages to the RP. Therefore, the RP can obtain information about all multicast sources and group members. With network expansion, administrators divide a PIM-SM network into multiple PIM-SM domains to facilitate control of multicast resources. In this case, the RP in a PIM-SM domain cannot obtain multicast source information in other PIM-SM domains. MSDP is introduced to solve this problem.

MSDP establishes MSDP peers between routers (usually RPs) in different PIM-SM domains to exchange Source-Active (SA) messages, so that the peers share multicast source information. MSDP allows multicast users in a PIM-SM domain to receive multicast data from multicast sources in other domains.


For details about PIM-SM, see PIM (IPv4) Configuration.

MSDP sets up peer relationships between Internet Service Provider (ISP) networks. In general, an ISP does not want to rely on other ISPs to provide services to its own users. The ISP wants to improve the network security and prevent complaints on service interruption caused by RP faults of other ISPs' networks. MSDP allows ISPs to exchange multicast data with the Internet using RPs.

MSDP is developed to implement inter-domain multicast. When MSDP is enabled on devices within a PIM-SM domain, it has another function: Anycast RP. Anycast RP supports several RPs with the same address in a PIM-SM domain. MSDP peer relationships are established between these RPs so that the multicast source can register to the closest RP and the multicast receiver can join the closest RP. In this manner, burdens on a single RP are released, and RP backup is implemented.


MSDP implements inter-domain multicast and provides the following advantages for ISPs:
  • A PIM-SM domain provides services using the local RPs, decreasing the dependency on RPs in other PIM-SM domains. MSDP controls whether source information in a domain is transmitted to another domain, improving network security.
  • If there are only receivers in a domain, the receivers can receive multicast data when they report the group memberships in the local PIM-SM domain but not on the entire network.
  • Devices in a PIM-SM domain do not need to maintain multicast source information and routing entries on the entire network, saving system resources.
Updated: 2019-08-09

Document ID: EDOC1000041694

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