Enabling Igmp Snooping Querier; Configuring Igmp Queries And Responses - HP A5500 SI Switch Series Configuration Manual

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.
Follow these steps to enable IGMP snooping querier:
To do...
Enter system view
Enter VLAN view
Enable IGMP snooping querier
CAUTION:
It is meaningless to configure an IGMP snooping querier in a multicast network that runs IGMP.
Although an IGMP snooping querier does not participate in IGMP querier elections, it might affect
IGMP querier elections because it sends IGMP general queries with a low source IP address. For more
information about IGMP querier, see the chapter "IGMP configuration."

Configuring IGMP queries and responses

You can set the IGMP general query interval based on actual conditions of the network.
After 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.
For IGMP general queries, configure the maximum response time to fill the Max Response time
•
field.
For IGMP group-specific queries, configure the IGMP last-member query interval to fill the Max
•
Response time field. Namely, for IGMP group-specific queries, the maximum response time equals
to the IGMP last-member query interval.
Configuring IGMP queries and responses globally
Follow these steps to configure IGMP queries and responses globally:
To do...
Enter system view
Use the command...
system-view
vlan vlan-id
igmp-snooping querier
Use the command...
system-view
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Remarks
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Required
Disabled by default
Remarks
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