103
Step
Command
Remarks
4.
Enable insertion of the
Router-Alert option into
IGMP messages.
igmp send-router-alert
By default, IGMP messages carry
the Router-Alert option.
Configuring IGMP query and response parameters
On startup, the IGMP querier sends IGMP general queries at the startup query interval, which is
one-quarter of the IGMP general query interval. The number of queries, or the startup query count, is
user configurable.
After startup, the IGMP querier periodically sends IGMP general queries at the IGMP general query
interval to examine for multicast group members on the network. You can modify the IGMP general
query interval based on actual condition of the network.
The IGMPv2 querier sends IGMP group-specific queries at the IGMP last-member query interval
when it receives an IGMP leave message. The IGMPv3 querier sends IGMP
group-and-source-specific queries at the IGMP last-member query interval when it receives a
multicast group and multicast mapping change report. The number of queries, or the last-member
query count, equals the robustness variable, which is the maximum number of packet
retransmissions.
A multicast listening host starts a delay timer for each multicast group it has joined when it receives
an IGMP query (general query, group-specific query, or group-and-source-specific query). The timer
is initialized to a random value in the range of 0 to the maximum response time derived in the IGMP
query. When the timer value decreases to 0, the host sends an IGMP report to the corresponding
multicast group.
To speed up the response of hosts to IGMP queries and avoid simultaneous timer expirations
causing IGMP report traffic bursts, you must properly set the maximum response time.
•
For IGMP general queries, the maximum response time is set by the
max-response-time
command.
•
For IGMP group-specific queries and IGMP group-and-source-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 when the
other querier present interval expires, it considers that the querier as having failed and starts a new
querier election. Otherwise, the non-querier router resets the other querier present timer.
Configuration guidelines
•
To avoid frequent IGMP querier changes, set the other querier present interval greater than the
IGMP general query interval.
•
To avoid incorrect multicast group member removals, set the IGMP general query interval
greater than the maximum response time for IGMP general queries.
•
The configurations of the maximum response time for IGMP general queries, the IGMP last
member query interval and the IGMP other querier present interval are effective only for
IGMPv2 and IGMPv3.
Configuration procedure
To configure IGMP query and response parameters globally:
Step
Command
Remarks
1.
Enter system view.
system-view
N/A
2.
Enter public network IGMP
view or VPN instance IGMP
igmp
[
vpn-instance
vpn-instance-name
]
N/A
