MSDP Deployment

General Guidelines for MSDP

In GÉANT2 the Multicast Source Discovery Protocol is used to communicate the availability of multicast sources between Autonomous Systems. MSDP-speaking PIM-SM RPs flood knowledge of active sources to each other. MSDP-speaking RPs communicate with each other via TCP sessions. It is possible that the Source Active messages transmitted over the TCP session contain a packet of data, which the MSDP-speaking RPs can forward down their group-specific shared trees, with the SPT-bit set.

The Multicast Source Discovery Protocol (MSDP) is developed for support the Any Source Multicast model. It should not be used in a Source Specific Multicast context.

MSDP uses the multicast routing (see MBGP guidelines) table in order to determine whether to accept or not the source announcement.

Enabling MSDP without MBGP can lead to multicast "black hole", thus no Multicast traffic can go out from that domain.

An MSDP mesh group can be used in the stub PIM domain where MBGP peering is not possible, and also for reducing the SA storm in single domain.

GÉANT2-Specific MSDP Guidelines

MSDP should be enabled on all GÉANT2 routers, on their Loopback0 interface respectively. On Juniper routers, the routing table associated to MSDP (for exported and imported routes) is inet.4.

The GÉANT2 network peers with other PIM domains by way of external MSDP (eMSDP) sessions. The peering sessions are configured in one of three ways:

• Single Access circuit
  A single eMSDP session is configured between physical interfaces for all instances where the GÉANT2 network peers with another PIM domain by way of a single point of access.
  
  
• Singly Homed Dual Access circuits
  In cases where there are two circuits (primary and back-up) between the neighbour PIM domain's router and one GÉANT2 router, a single eMSDP session is configured between the loopback interfaces of the two routers.
  
  
• Dual Homed Access Circuit
  In cases where GÉANT2 has multiple access circuits with a PIM domain that terminate on different routers, then multiple eMSDP peerings are established between the physical interfaces of the GÉANT2 routers and those in the external domain.

The RPF check for SAs learned from another PIM domain is carried out purely on the AS path to the originator of the SA.