Protocol-Independent Multicast (Pim) - D-Link DES-3326 User Manual

DES-3326 Layer 3 Fast Ethernet Switch User's Guide
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 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 (PIM)

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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Switch Management and Operating Concepts