Specifications

195
DCS-3950 series Ethernet switch manual
Chapter 11 IGMP Snooping
11.1 Introduction to IGMP Snooping
IGMP (Internet Group Management Protocol) is a protocol used in IP multicast. IGMP
is used by multicast enabled network device (such as a router) for host membership query,
and by hosts that are joining a multicast group to inform the router to accept packets of a
certain multicast address. All those operations are done through IGMP message
exchange. The router will use a multicast address (224.0.0.1) that can address to all hosts
to send a IGMP host membership query message. If a host wants to join a multicast group,
it will reply to the multicast address of that a multicast group with a IGMP host
membership reports a message.
IGMP Snooping is also referred to as IGMP listening. The switch prevents multicast
traffic from flooding through IGMP Snooping, multicast traffic is forwarded to ports
associated to multicast devices only. The switch listens to the IGMP messages between
the multicast router and hosts, and maintains multicast group forwarding table based on
the listening result, and can then decide to forward multicast packets according to the
forwarding table.
DCS-3950 series switch provides IGMP Snooping and is able to send a query from
the switch so that the user can use DCS-3950 series switch in IP multicast.
11.2 IGMP Snooping Configuration
11.2.1 IGMP Snooping Configuration Task List
1. Enable IGMP Snooping
2. Configure IGMP Snooping
1. Start IGMP Snooping function
Command Explanation
Global configuration mode
Ip igmp snooping
No ip igmp snooping
Start IGMP Snooping function; the ‘ No ip
igmp snooping’ command will shut down
the IGMP snooping function globally.
2． Configure IGMP Snooping
Command Explanation
Global configuration mode
Ip igmp snooping vlan <vlan-id>
No ip igmp snooping vlan <vlan-id>
Start IGMP Snooping function on the
specified vlan.’ No ip igmp snooping vlan