Operation Manual – Multicast Protocol
H3C S3610&S5510 Series Ethernet Switches
Chapter 5 IGMP Configuration
5-11
To do...
Use the command...
Description
Configure the interface to
discard any IGMP
message that does not
carry the Router-Alert
option
igmp
require-router-alert
Optional
By default, the device
does not check the
Router-Alert option.
Enable the insertion of the
Router-Alert option into
IGMP messages
igmp send-router-alert
Optional
By default, IGMP
messages carry the
Router-Alert option.
5.4.3 Configuring IGMP Query and Response Parameters
The IGMP querier periodically sends IGMP general queries at the “IGMP query
interval” to determine whether any multicast group member exists on the network. You
can tune the IGMP general query interval based on actual condition of the network.
On startup, the IGMP querier sends “startup query count” IGMP general queries at the
“startup query interval”, which is 1/0/5 of the “IGMP query interval”. 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”. Both startup query
count and last member query count are set to the IGMP querier robustness variable.
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.
z
For IGMP general queries, you can configure the maximum response time to fill
their Max Response time field.
z
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
