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Chapter 9
Multicast
gives the switch the CGMP message. With the CGMP message, the switch
can assign the multicast group to the port of the requesting host. You can see
the entire process in Figure 9.11.
F I G U R E 9 . 1 1
CGMP Join process
Host Management
Host management is performed by the router. The router continues to
receive IGMP messages from the host. Then the router converts the message
into a CGMP message and forwards it to the switch. The switch then per-
forms the port maintenance as directed by the router. This process is fol-
lowed for the multiple types of message that the host can generate.
The CGMP Leave process is done in the same manner. The router receives
the request and then informs the switch that the multicast group address
needs to be removed from the Content Addressable Memory (CAM) table
for the host's port.
Routing Multicast Traffic
U
p to this point, we have been discussing the host side of multicast.
You have learned how hosts interact with switches and routers to join multi-
cast groups and receive the traffic. It is now time to move on to discuss how
HostA sends
IGMP report for
224.2.165.145.
Router receives report,
creates GDA and USA,
and enables multicast
forwarding on interface FE0/0.
HostB
HostA
HostC
Router1
Switch 1
1
2
2
1
3
Switch receives CGMP Join.
Establishes a multicast CAM
entry for port 2/1.
3
2/1
2/2
V1
2/3
FE0/0
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