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5-4
C
HAPTER
5: I
NTERNET
G
ROUP
M
ANAGEMENT
P
ROTOCOL
(IGMP) S
NOOPING
Figure 5-2 shows the format of a typical IGMP snooping version 1
message that is received after an IGMP snooping query in a multicast
group has been completed.
Figure 5-2
Format of an IGMP Version 1 Message
When IGMP snooping is running on a CoreBuilder
®
5000 hub, it allows
multicast traffic to ports where:
■
IGMP Report packets for that multicast group have been observed.
■
Multicast routing protocols have been observed.
Figure 5-3 shows a typical multicast packet path after snooping has
occurred.
Figure 5-3
Multicast Packet Path after Snooping
0 3 4 7 8 15 16 31
4-bit
IGMP
Version
4-bit
IGMP
Type
8-bit
Unused
16-bit checksum
32-bit group address (Class D IP Address)
Host 2
Host 1Host 3
Multicast
Router
Host 3 sends a
Multicast Packet
CoreBuilder
®
5000 Hub