622 CHAPTER 46: IGMP CONFIGURATION
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:
Configuring IGMP query and response parameters on an interface
Follow these steps to configure IGMP query and response parameters on an
interface:
To do… Use the command… Description
Enter system view system-view -
Enter IGMP view igmp -
Configure the IGMP query
interval
timer query interval Optional
60 seconds by default
Configure the IGMP querier
robustness variable
robust-count robust-value Optional
2 by default
Configure the maximum
response time for IGMP
general queries
max-response-time interval Optional
10 seconds by default
Configure the IGMP last
member query interval
Last-member-query-interva
l interval
Optional
1 second by default
Configure the other querier
present interval
timer
other-querier-present
interval
Optional
For the system default, see
“Note” below.
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