3com S7906E 安装指导
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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.
z
For IGMP general queries, you can configure the maximum response time to fill their Max
Response time field.
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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...
Use the command...
Remarks
Enter system view
system-view
—
Enter public instance IGMP
view or VPN instance IGMP
view
view or VPN instance IGMP
view
igmp [ vpn-instance
vpn-instance-name ]
vpn-instance-name ]
—
Configure the startup query
interval
interval
startup-query-interval interval
Optional
For the system default, see
“Note” below.
“Note” below.
Configure the startup query
count
count
startup-query-count value
Optional
For the system default, see
“Note” below.
“Note” below.
Configure the IGMP query
interval
interval
timer query interval
Optional
60 seconds by default
Configure the IGMP querier
robustness variable
robustness variable
robust-count robust-value
Optional
2 by default
Configure the maximum
response time for IGMP
general queries
response time for IGMP
general queries
max-response-time interval
Optional
10 seconds by default
Configure the IGMP last
member query interval
member query interval
last-member-query-interval
interval
interval
Optional
1 second by default