D-Link DES-3326SR User Manual page 108

DES-3326SR Layer 3 Fast Ethernet Switch User's Guide
delivery tree to be reactivated. This allows for lower latency
when a leaf router adds a new member to a multicast
membership group. Graft messages are forwarded one hop
(one router) back at a time toward a multicast source until they
reach a router that is on an active branch of the multicast
delivery tree.
If there is more than one multicast router on a network, the
one that has the shortest path back to the multicast source is
elected to forward multicast packets from that source. All
other routers will discard multicast packets from that source.
If two multicast routers on a network have the same distance
back to a multicast source, the router with the lowest IP
address is elected.
DVMRP also supports tunnel interfaces, where two multicast
routers are connected through a router that cannot process
multicast packets. This allows multicast packets to cross
networks with routers that are not multicast-aware.
Protocol-Independent Multicast – Dense Mode
There are two protocols in Protocol Independent Multicast
(PIM), Protocol Independent Multicast-Dense Mode (PIM-DM)
which is used when the multicast destinations are closely
spaced, and Protocol Independent Multicast-Sparse Mode (PIM-
SM) which is used when the multicast destinations are spaced
further apart. PIM-DM is most commonly implemented in an
intranetwork (LAN) where the distance between users is
minimal.
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