Chapter 30 Msdp Configuration; Msdp Overview; Introduction - 3Com 8800 Configuration Manual

3Com Switch 8800 Configuration Guide

Chapter 30 MSDP Configuration

30.1 MSDP Overview

30.1.1 Introduction

Multicast source discovery protocol (MSDP) is used to discover multicast source
information in other PIM-SM domains. No ISP would like to forward multicast traffic
depending on the RP of competitors, though it has to obtain information from the source
and distribute it among its members, regardless of the location of the source RP. MSDP
is proposed to solve this problem. MSDP describes interconnection mechanism of
multiple PIM-SM domains. MSDP allows the RPs of different domains to share the
multicast source informatin, but all these domains must use PIM-SM as their
intro-domain multicast routing procotocol.
A RP configured with MSDP peer notifies all of its MSDP peers of the active multicast
source message in its domain via SA (Source Active) message. In this way, multicast
source information in a PIM-SM domain is transmitted to another PIM-SM domain.
MSDP peer relationship can be established between RPs in different domains or in a
same domain, between a RP and a common router, or between common routers. The
connection between MSDP peers is TCP connection.
MSDP makes a PIM-SM domain independent of the RP in another PIM-SM domain.
After getting multicast source information in that domain, the receiver here can join
directly to the SPT of the multicast source in that domain.
Another application of MSDP is Anycast RP. In a domain, configure a certain interface
(usually Loopback interface) on different routers with a same IP address; designate
these interfaces as C-RPs; and create MSDP peer relationship among them. After the
unicast route convergence, the multicast source can select the nearest RP for
registration, and the receiver can also select the nearest RP to add into its RPT. The
RPs exchange individual registration source information via MSDP peers. Therefore,
every RP knows all multicast sources of the entire domain; and every receiver on each
RP can receive multicast data from all the multicast sources in the entire domain.
By initiating registration and RPT joining to the nearest RP, MSDP implements RP load
sharing. Once an RP turns invalid, its original registered source and receivers will
select another nearest RP, implementing redundant RP backup.
In addition, MSDP only accepts the SA messages from the correct paths and excludes
redundant SA messages through RPF check mechanism, and prevents the flooding of
SA messages among MSDP peers by configuring Mesh Group.
Chapter 30 MSDP Configuration
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