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MSDP C
ONFIGURATION
MSDP Overview
Introduction
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 multicast source RP. MSDP is proposed
to solve this problem. Multicast source discovery protocol (MSDP) describes
interconnection mechanism of multiple PIM-SM domains. It is used is to discover
multicast source information in other PIM-SM domains. MSDP allows the RPs of
different domains to share the multicast source information, but all these domains
must use PIM-SM as their intro-domain multicast routing protocol.
though it has to obtain information from the source and distribute it among its
members, regardless of the location of the multicast source RP. MSDP is proposed
to solve this problem. Multicast source discovery protocol (MSDP) describes
interconnection mechanism of multiple PIM-SM domains. It is used is to discover
multicast source information in other PIM-SM domains. MSDP allows the RPs of
different domains to share the multicast source information, but all these domains
must use PIM-SM as their intro-domain multicast routing protocol.
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.
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.
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.
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.
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.
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.
excludes redundant SA messages through RPF check mechanism, and prevents the
flooding of SA messages among MSDP peers by configuring Mesh Group.