HP 6125G HP 6125G & 6125G/XG Blade Switches IP Multicast Configuration - Page 98

Configuring IGMP query and response parameters, Configuration guidelines, Configuration procedure

Page 98 highlights

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 check 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-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 • In the configuration, make sure that the other querier present interval is greater than the IGMP general query interval. Otherwise, the IGMP querier might change frequently on the network. • Also make sure that the IGMP general query interval is greater than the maximum response time for IGMP general queries. Otherwise, multicast group members might be wrongly removed. • 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 1. Enter system view. 2. Enter IGMP view. 3. Configure the IGMP querier's robustness variable. Command system-view igmp robust-count robust-value Remarks N/A N/A 2 by default. 87

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87
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 check 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—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
In the configuration, make sure that the other querier present interval is greater than the IGMP
general query interval. Otherwise, the IGMP querier might change frequently on the network.
Also make sure that the IGMP general query interval is greater than the maximum response time for
IGMP general queries. Otherwise, multicast group members might be wrongly removed.
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 IGMP view.
igmp
N/A
3.
Configure the IGMP querier’s
robustness variable.
robust-count
robust-value
2 by default.