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Summary: Multicast Routing in Datagram Internetworks
and Extended LANs
STEPHEN E. DEERING and DAVID R. CHERITON
Stanford University
Multicasting, the transmission of a packet to a group of hosts, is an important service for improving
the efficiency and robustness of distributed systems and applications. Although multicast capability
is available and widely used in local area networks, when those LANs are interconnected by store-
and-forward routers, the multicast service is usually not offered across the resulting internetwork. To
address this limitation, we specify extensions to two common internetwork routing algorithms-
distance-vector routing and link-state routing-to support low-delay datagram multicasting beyond
a single LAN. We also describe modifications to the single-spanning-tree routing algorithm commonly
used by link-layer bridges, to reduce the costs of multicasting in large extended LANs. Finally, we
discuss how the use of multicast scope control and hierarchical multicast routing allows the multicast
service to scale up to large internetworks.
Categories and Subject Descriptors: C.2.1 [Computer-Communication Networks]: Network
Architecture and Design-network topology, packet networks, store and forward networks; C.2.2
[Computer-Communication Networks]: Network Protocols-protocol architecture; C.2.5
[Computer-Communication Networks]: Local Networks
General Terms: Algorithms, Design, Performance
Additional Key Words and Phrases: Broadcast, datagram, distance-vector routing, hierarchical
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