Multicast allows a single source to simultaneously exchange traffic with many other machines.
Multicast is commonly used for broadcasting - a single computer can provide a audio or video feed to thousands of listeners. Multicast can also be used for group videoconferencing, such as between the Access Grid immersive videoconferencing rooms.
Access by sites to multicast traffic requires a request to the AARNet Network Operations Centre.
AARNet's multicast service uses the IETF's inter-domain multicast protocols, namely: MBGP, PIM-SM and MSDP.
To allow multicast traffic to take a differing path from unicast traffic, BGP runs a distinct multicast address family. BGP which seeks to negotiate this address family is named “multiprotocol BGP” or MBGP. If a site does not wish to engineer multicast and unicast traffic doesn differing paths then simply use the same routing policies for unicast and multicast BGP route filtering.
Protocol Independent Multicast (PIM) uses the unicast forwarding table (populated by some unicast routing protocol) to build the reverse path forwarding tree for each source. Multicast traffic is forwarded down into this tree.
Protocol Independent Multicast – Sparse Mode (PIM-SM) is a refinement where sources explicitly register with the PIM-SM rendevous point. This allows the tree to be built correctly from the beginning, thus avoiding forwarding multicast traffic down paths where there are no participants. AARNet runs PIM-SM internally. We recommend that sites do the same.
AARNet implements administrative scoping.