DES-3326S Layer 3 Fast Ethernet Switch User’s Guide
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Switch Management and Operating Concepts
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.
Routing Protocols
Routing Information Protocol (RIP)
The Routing Information Protocol is a distance-vector routing
protocol. There are two types of network devices running RIP –
active and passive. Active devices advertise their routes to
others through RIP messages, while passive devices listen to
these messages. Both active and passive routers update their
routing tables based upon RIP messages that active routers
exchange. Only routers can run RIP in the active mode.
Every 30 seconds, a router running RIP broadcasts a routing
update containing a set of pairs of network addresses and a
