3Com Switch 8800 Advanced Software V5 Configuration Guide

550 CHAPTER 41: IGMP SNOOPING CONFIGURATION
■ Source address of IGMP general queries
■ Source address of IGMP group-specific queries
■ Whether to enable IGMP report suppression
Enabling IGMP Snooping
Querier
In an IP multicast network running IGMP, a Layer 3 multicast device acts as the
IGMP querier, which periodically sends IGMP queries so that all Layer 3 multicast
devices can create and maintain multicast forwarding entries at the network layer,
thus to forward multicast traffic correctly at the network layer.
In a network that does not comprise Layer 3 multicast devices, however, it is a
problem to implement an IGMP querier, because Layer 2 devices do not support
IGMP. To solve this problem, you can enable the IGMP Snooping querier function
on a Layer 2 device so that it can work as an IGMP Snooping querier to create and
maintain multicast forwarding entries at the data link layer.
Follow these steps to enable IGMP Snooping querier:
c
CAUTION:
■ An IGMP Snooping querier does not take part in IGMP querier elections.
■ It is meaningless to configure an IGMP Snooping querier in a multicast network
running IGMP. It may affect IGMP querier elections because it sends IGMP
general queries with a low source IP address.
Configuring IGMP
Timers
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
corresponding timers expires 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
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