H3C Technologies H3C S10500 Series Switches - Manual (Page 124)

109
To do... Use the command... Remarks
Enable insertion of the Router-Alert
option into IGMP messages
igmp send-router-alert
Required
By default, IGMP messages carry
the Router-Alert option.
Configuring IGMP query and response parameters
The IGMP querier’s robustness variable defines the maximum number of attempts for transmitting IGMP
general queries, group-specific queries, or group-and-source-specific queries in case of packet loss due
to network problems. A greater value of the robustness variable makes the IGMP querier “more robust”,
but results in longer multicast group timeout time.
On startup, the IGMPv1/v2/v3 querier sends “startup query count” IGMP general queries at the “startup
query interval”.
The IGMPv1/v2/v3 querier periodically sends IGMP general queries at the “IGMP general 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.
After receiving an IGMP leave message, the IGMPv2 querier sends “last-member query count” IGMP
group-specific queries at the “IGMP last-member query interval”. After receiving an IGMP report that
shows relation changes between multicast groups and multicast sources, the IGMPv3 querier sends
“last-member query count” IGMP group-and-source-specific queries at the “IGMP last-member query
interval”. The value of the “last-member query count” equals the value of the robustness variable.
After receiving an IGMP query (general query, group-specific query, or group-and-source-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 and IGMP group-and-source-specific queries, you can configure
the IGMP last-member query interval to fill their Max Response time field. Namely, for IGMP
group-specific queries and IGMP group-and-source-specific queries, the maximum response time
equals to the IGMP last-member query interval.
When multiple multicast routers exist on the same subnet, the IGMP querier sends IGMP queries. If a
non-querier router receives no IGMP query from the querier within the “other querier present interval”, it
assumes that the querier has expired and a new querier election process begins. 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 —