9.4 Multicast Routing Protocols
9.4.3
Multicast open shortest path first

Described in RFC 1584, MOSPF is intended for use within a single routing domain, such as a network controlled by a single organization. MOSPF is dependent on the use of OSPF as the accompanying unicast routing protocol. In an OSPF/MOSPF network, each router maintains an up-to-date image of the topology of the entire network. MOSPF works by including multicast information in OSPF link-state advertisements. An MOSPF router learns which multicast groups are active on which LANs.

This link-state information is used to construct multicast distribution trees. MOSPF builds a distribution tree for each (source, group) pair and computes a tree for active sources sending to the group. The tree state is cached, and trees must be recomputed when a link-state change occurs or when the cache times out.

MOSPF is best suited for environments that have relatively few (source, group) pairs active at any given time. This protocol will work less well in environments that have many active sources or environments that have unstable links.

Note: Cisco routers do not support MOSPF.