564 CHAPTER 42: IGMP SNOOPING CONFIGURATION
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:
c
CAUTION: 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.
■ For IGMP general queries, you can configure the maximum response time to fill
their Max Response time field.
■ 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.
Configuring IGMP queries and responses globally
Follow these steps to configure IGMP queries and responses globally:
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
To do… Use the command… Remarks
Enter system view system-view -
Enter IGMP Snooping view igmp-snooping -
Configure the maximum response
time to IGMP general queries
max-response-time
interval
Optional
10 seconds by default
Configure the IGMP last-member
query interval
last-member-query-inter
val interval
Optional
1 second by default
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