3Com S7906E - Switch, Configuration Manual

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1-2
Figure 1-1 Before and after IGMP snooping is enabled on the Layer 2 device
Multicast packet transmission
without IGMP Snooping
Source
Multicast router
Host A
Receiver
Host B
Host C
Receiver
Multicast packets
Layer 2 switch
Multicast packet transmission
when IGMP Snooping runs
Source
Multicast router
Host A
Receiver
Host B
Host C
Receiver
Layer 2 switch
IGMP snooping forwards multicast data to only the receivers requiring it at Layer 2. It brings the
following advantages:
z
Reducing Layer 2 broadcast packets, thus saving network bandwidth.
z
Enhancing the security of multicast traffic.
z
Facilitating the implementation of per-host accounting.
Basic Concepts in IGMP Snooping
IGMP Snooping related ports
As shown in Figure 1-2 , Router A connects to the multicast source, IGMP snooping runs on Switch A
and Switch B, and Host A and Host C are receiver hosts (namely, multicast group members).
Figure 1-2 IGMP snooping related ports
Router A Switch A
Switch B
GE2/0/1 GE2/0/2
GE2/0/3
GE2/0/1
GE2/0/2
Receiver
Receiver
Host A
Host B
Host C
Host D
Source
Multicast packets
Router port
Member port
Ports involved in IGMP snooping, as shown in Figure 1-2 , are described as follows: