Filter
Top Products
7-24
Advanced Concepts
IP Multicast (IGMP)
Advanced Concepts
Once the switch learns the port location of the hosts belonging to any partic-
ular multicast group, it can direct group traffic to only those ports, resulting
in bandwidth savings on ports where group members do not reside. The
following example illustrates this operation.
Figure 7-13 shows a network running IGMP.
■ PCs 1 and 4, Switch #2, and all of the routers are members of an IP
multicast group. (The routers operate as queriers.)
■ Switch #1 ignores IGMP traffic and does not distinguish between IP
multicast group members and non-members. Thus, it is sending large
amounts of unwanted multicast traffic out the ports to PCs 2 and 3.
■ Switch #2 is recognizing IGMP traffic and learns that PC #4 is in the IP
multicast group receiving multicast data from the video server (PC X).
Switch #2 then sends the multicast data only to the port for PC #4, thus
avoiding unwanted multicast traffic on the ports for PCs #5 and #6.
Figure 7-13. The Advantage of Using IGMP
PC X
Video
Server
Router
Router
PC #1
Video
Client
Switch # 1
Router
Router
Switch # 2
PC #2
PC #3
PC # 4
Video
Client
PC # 5
PC #6
Multicast
Data Stream
IGMP is NOT
Running Here
IGMP IS
Running Here
SEDONA.BK : sed_7.fm5 Page 24 Thursday, February 27, 1997 10:11 AM