IP multicast routing protocols

IP multicast routing protocols allow a set of multicast routers to build or join multicast distribution trees when a terminal requests to receive traffic from a certain group. A distribution tree specifies a unique transmission path between the source of multicast traffic and each subnet that contains at least one member of the group. By controlling the path that multicast traffic must follow in the network in order to reach all receivers, distribution trees ensure efficient transmission of multicast traffic within the network (only one copy of each packet is transmitted on each branch of the tree).

Several multicast routing protocols have been defined, each with its own particular characteristics, making them suitable for use in different environments. Similar to unicast routing protocols, which are divided into Interior Gateway Protocol (IGP) and Exterior Gateway Protocol (EGP), dynamic multicast routing protocols are classified into two main families:

• dynamic routing protocols that allow the construction of limited distribution trees within a multicast domain: these are the MIGP (Multicast Interior Gateway Protocol) intra-domain multicast routing protocols;

  Note :

  the notion of IP multicast domain is an administrative notion, defining a set of IP routers activating the same multicast routing protocol. In theory, this notion is independent of the notion of unicast IP domain; in reality, however, the notion of IP multicast domain generally coincides with that of Autonomous System (AS).

• dynamic routing protocols that connect multicast domains by building distribution trees that span several domains: these are the MEGP (Multicast Exterior Gateway Protocol) inter-domain multicast routing protocols.

This great variety and protocol richness sometimes makes it difficult to understand how all these protocols work and how they cooperate or interoperate. A detailed overview of the most important multicast routing protocols in IPv4 and IPv6 networks is given here.

As such, this dossier is structured around the following elements:

• a detailed description and analysis of the main multicast routing protocols currently in use within a multicast domain, including PIM-SM, PIM-DM, PIM-BIDIR, PIM-SSM, DVMRP and MOSPF, along with an analysis of the advantages, disadvantages and current deployments of each;

• A presentation of the different RP rendezvous point router discovery mechanisms, including BSR, Auto-RP, Anycast-RP, Embedded-RP ;

• finally, a description of solutions for multicast...