Multicast Routing Protocols - D-Link DES-3326SR User Manual

DES-3326SR Layer 3 Fast Ethernet Switch User's Guide
removes all of the prune information it has gathered from it's
memory, and the entire process repeats. This gives all
subsequent routers on the network a chance to receive
multicast packets from all multicast sources on the network. It
also gives all users a chance to join a given multicast group.

Multicast Routing Protocols

This section contains an overview of two multicast routing
protocols – Distance Vector Multicast Routing Protocol
(DVMRP), and Protocol Independent Multicast-Dense Mode
(PIM-DM). The most commonly used routing protocol (not a
multicast routing protocol), the Routing Information Protocol, is
discussed in a later section.
Distance Vector Multicast Routing Protocol (DVMRP)
The Distance Vector Multicast Routing Protocol (DVMRP) was
derived from the Routing Information Protocol (RIP) with the
introduction of multicast delivery trees constructed from
information about the 'distance' from the local router back
toward the multicast source. DVMRP uses an RPM algorithm
to construct its multicast delivery trees.
The first multicast packet received by a multicast router using
DVMRP is flooded to all interfaces except the one on which the
packet was received. Subsequent prune messages are used to
prune branches of the delivery tree that are either not on the
shortest path back to the multicast source, or that have no
active multicast group members. A 'graft' message is added
that allows a previously pruned branch of the multicast
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