HP A5500 EI Switch Series, Руководство по настройке

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14
IGMP snooping configuration
IGMP snooping overview
IGMP snooping is a multicast constraining mechanism that runs on Layer 2 devices to manage and
control multicast groups.
Principle of IGMP snooping
By analyzing received IGMP messages, a Layer 2 switch that runs IGMP snooping establishes mappings
between ports and multicast MAC addresses, and forwards multicast data based on these mappings.
When IGMP snooping is not running on the switch, multicast packets are flooded to all devices at Layer
2. When IGMP snooping runs on the switch, multicast packets for known multicast groups are multicast
to the receivers, rather than being broadcast to all hosts, at Layer 2.
Figure 11 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 that require the data at Layer 2. It has the
following advantages:
•
Reducing Layer 2 broadcast packets, saving network bandwidth
•
Enhancing the security of multicast traffic
•
Facilitating the implementation of per-host accounting