3Com S7906E Configuration Manual page 1006

Upon receiving an IGMP leave message, the IGMP querier sends "last member query count" IGMP
group-specific queries at the "IGMP last member query interval". IGMP is robust to "robustness variable
minus 1" packet losses on a network. Therefore, a greater value of the robustness variable makes the
IGMP querier "more robust", but results in a longer multicast group timeout time.
Upon receiving an IGMP query (general query or group-specific query), a host starts a delay 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, which is derived from the Max Response Time field in the IGMP query. 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 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 group-specific queries, the maximum response
time equals the IGMP last member query interval.
When multiple multicast routers exist on the same subnet, the IGMP querier is responsible for sending
IGMP queries. If a non-querier router receives no IGMP query from the querier within the "other querier
present interval", it will assume the querier to have expired and a new querier election process is
launched; otherwise, the non-querier router will reset its "other querier present timer".
Configuring IGMP query and response parameters globally
Follow these steps to configure IGMP query and response parameters globally:
To do...
Enter system view
Enter public instance IGMP
view or VPN instance IGMP
view
Configure the startup query
interval
Configure the startup query
count
Configure the IGMP query
interval
Configure the IGMP querier
robustness variable
Configure the maximum
response time for IGMP
general queries
Configure the IGMP last
member query interval
Use the command...
system-view
igmp [ vpn-instance
vpn-instance-name ]
startup-query-interval interval
startup-query-count value
timer query interval
robust-count robust-value
max-response-time interval
last-member-query-interval
interval
1-14
Remarks
—
—
Optional
For the system default, see
"Note" below.
Optional
For the system default, see
"Note" below.
Optional
60 seconds by default
Optional
2 by default
Optional
10 seconds by default
Optional
1 second by default