H3C Technologies H3C WX6000 Series Access Controllers - Manual (Page 329)

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Enabling IGMP Snooping Querier
In an IP multicast network running IGMP, a multicast router or Layer 3 multicast switch is responsible for
sending IGMP general queries, so that all Layer 3 multicast devices can establish and maintain
multicast forwarding entries, thus to forward multicast traffic correctly at the network layer. This router or
Layer 3 switch is called IGMP querier.
However, a Layer 2 multicast switch does not support IGMP, and therefore cannot send general queries
by default. By enabling IGMP Snooping on a Layer 2 switch in a VLAN where multicast traffic needs to
be Layer-2 switched only and no multicast routers are present, the Layer 2 switch will act as the IGMP
Snooping querier to send IGMP queries, thus allowing multicast forwarding entries to be established
and maintained at the data link layer.
Follow these steps to enable IGMP Snooping querier:
To do... Use the command... Remarks
Enter system view system-view —
Enter VLAN view vlan vlan-id —
Enable IGMP Snooping querier igmp-snooping querier
Required
Disabled by default
It is meaningless to configure an IGMP Snooping querier in a multicast network running IGMP. Although
an IGMP Snooping querier does not take part in IGMP querier elections, it may affect IGMP querier
elections because it sends IGMP general queries with a low source IP address.
Configuring IGMP Queries and Responses
You can tune the IGMP general query interval based on actual condition of the network.
Upon receiving an IGMP query (general query or group-specific query), a host starts a timer for each
multicast group it has joined. This timer is initialized to a random value in the range of 0 to the maximum
response time (the host obtains the value of the maximum response time from the Max Response Time
field in the IGMP query it received). When the timer value comes down to 0, the host sends an IGMP
report to the corresponding multicast group.
An appropriate setting of the maximum response time for IGMP queries allows hosts to respond to
queries quickly and avoids bursts of IGMP traffic on the network caused by reports simultaneously sent
by a large number of hosts when the corresponding timers expire simultaneously.
z
For IGMP general queries, you can configure the maximum response time to fill their Max
Response time field.
z
For IGMP group-specific queries, you can configure the IGMP last-member query interval to fill
their Max Response time field. Namely, for IGMP group-specific queries, the maximum response
time equals to the IGMP last-member query interval.