3Com Switch 4800G 24-Port Configuration Manual page 564

564 C 42: IGMP S
HAPTER
c
Configuring IGMP
Queries and Responses
C
NOOPING ONFIGURATION
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...
Enter system view
Enter VLAN view
Enable IGMP Snooping
querier
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.
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...
Enter system view
Enter IGMP Snooping view
Configure the maximum response
time to IGMP general queries
Configure the IGMP last-member
query interval
Use the command...
system-view
vlan vlan-id
igmp-snooping querier
Use the command...
system-view
igmp-snooping
max-response-time
interval
last-member-query-inter
val interval
Remarks
-
-
Required
Disabled by default
Remarks
-
-
Optional
10 seconds by default
Optional
1 second by default