HP ProCurve Switch 212M Management And Configuration Manual page 104

Configuring the Switch
IP Multicast (IGMP) Service Features—Multimedia Traffic Control
Figure 6-19. The Advantage of Using IGMP
The next figure (6-20) shows a network running IP multicasting using IGMP
without a multicast router. In this case, the IGMP-configured switch runs as a
querier.
PCs 2, 5, and 6 are members of the same IP multicast group.
IGMP is configured on switches 3 and 4. Either of these switches can operate
as querier because a multicast router is not present on the network. (If an
IGMP switch does not detect a querier, it automatically assumes this role,
assuming the querier feature is enabled—the default—within IGMP.)
6-40
Router
Router
IGMP is NOT
Running Here
Switch # 1
PC #1
Video
PC #3
Client
PC #2
Router
Router
IGMP IS
Switch # 2
Running Here
PC # 4
Video
Client
PC # 5
Multicast
Data Stream
PC X
Video
Server
PC #6