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Configuring IGMP snooping querier
Before you configure IGMP snooping querier, complete the following tasks:
•
Enable IGMP snooping in the VLAN.
•
Determine the IGMP general query interval.
•
Determine the IGMP last-member query interval.
•
Determine the maximum response delay for IGMP general queries.
•
Determine the source address of IGMP general queries.
•
Determine the source address of IGMP group-specific queries.
Enabling IGMP snooping querier
In an IP multicast network that runs IGMP, a multicast router or Layer 3 multicast switch sends IGMP
queries, so that all Layer 3 multicast devices can establish and maintain multicast forwarding entries, in
order to forward multicast traffic correctly at the network layer. This router or Layer 3 switch is called the
"IGMP querier."
However, a Layer 2 multicast switch does not support IGMP, and therefore cannot send general queries
by default. When you enable IGMP snooping querier on a Layer 2 switch in a VLAN where multicast
traffic is switched only at Layer 2 and no multicast routers are present, the Layer 2 switch sends IGMP
queries, so that multicast forwarding entries can be established and maintained at the data link layer.
To enable IGMP snooping querier:
Step Command
Remarks
1.
Enter system view.
system-view
N/A
2.
Enter VLAN view.
vlan
vlan-id
N/A
3.
Enable IGMP snooping
querier.
igmp-snooping
querier
Disabled by default
IMPORTANT:
In a multicast network that runs IGMP, you do not need to configure an IGMP snooping querier because
it may affect IGMP querier elections by sending IGMP general queries with a low source IP address.
Configuring parameters for IGMP queries and responses
CAUTION:
In the configuration, make sure that the IGMP general query interval is larger than the maximum response
delay for IGMP general queries. Otherwise, multicast group members might be deleted by mistake.
You can modify the IGMP general query interval based on actual condition of the network.
A multicast listening host starts a timer for each multicast group that it has joined when it receives an
IGMP query (general query or group-specific query). This timer is initialized to a random value in the
range of 0 to the maximum response delay advertised in the IGMP query message. When the timer value
decreases to 0, the host sends an IGMP report to the multicast group.
