The invention provides a method and system for multicast packet routing, in which only selected routers in a network subset (in a preferred embodiment, those routers on the border of the domain) maintain routing information external to the network subset, while all other routers in the network subset (non-border routers) maintain only information regarding routing within the network subset, including which border routers are on the path from the multicast source device or to the destination devices. The network subset is preferably a domain or other routing domain. A multicast distribution tree is maintained, using protocol messages which are transmitted from leaf nodes toward a root of the tree, while data packets to be multicast are distributed from the root toward the leaf nodes. In each network subset, such as a routing domain, each multicast packet is associated with a multicast distribution tree. The multicast distribution tree is associated with an upstream border router (UBR) and a set of downstream border routers (DBRs). The UBR and DBRs maintain complete routing information for each multicast source device, while all other routers in the network subset maintain routing information only to the UBR and DBRs. A "JOIN" or "PRUNE" protocol message associates a particular UBR with a particular multicast source device, so that non-border routers within the network subset only have to maintain routing information to border routers, while still being able to correctly maintain a multicast distribution tree rooted at a node outside the network subset.
展开▼
