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Terminology and Concepts
893-01006-C
1-25
In Figure 1-9, the packets flow as follows:
• A single stream of packets flows from each IGMP group within the multicast
server into the router.
• The router knows that IGMP clients from each IGMP group exist in ELAN A,
so the router forwards a single copy of each IGMP stream to the BUS in
ELAN A.
• The BUS in ELAN A treats the multicast packets as broadcast packets and
forwards them to all of the LECs registered in the ELAN.
• LEC 1 forwards the packets from the IGMP group 1 flow to all of the Ethernet
clients in the switch that have joined IGMP group 1.
• LEC 1 forwards the packets from the IGMP group 2 flow to all of the Ethernet
clients in the switch that have joined IGMP group 2.
• The router knows that an IGMP client exists in ELAN B, so the router
forwards a single copy of the stream from IGMP group 2 to the BUS in
ELAN B.
• The BUS in ELAN B forwards the multicast packets to all of the LECs that
are registered within the ELAN.
• Only LEC 1 in ELAN B forwards the packets on to any Ethernet clients.
• LEC 2 does not have a client or instance of IGMP group 2, and it does not
forward any of the multicast packets from IGMP group 2 to any Ethernet
clients.
LEC 2 in ELAN B has an instance of IGMP group 3. No flows exist for IGMP
group 3. As a result, IGMP multicast traffic is neither received by LEC 2 nor
forwarded to any Ethernet clients.
Note:
IGMP group 1 packets are never forwarded to ports that have not joined
IGMP group 1, and the same is true for IGMP group 2 packets.