Adjust and Optimize IGMP Network

Configuration Condition

Before adjusting and optimizing the IGMP network, first complete the following task:

• Configure interface network layer address, making the neighboring node network layer reachable
• Enable the IGMP protocol

Configure Query Interval of General Group

IGMP querier periodically sends the general group query packets to maintain the group member relation. You can modify the interval of sending the IGMP general group query packets according to the actuality of the network.

Table 5–7 Configure the query interval of the general group

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  The genera query intervals of the devices on the same segment should try to keep consistent.
• The general group query interval should be larger than the maximum response time. Otherwise, the configuration cannot succeed.

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Configure Robustness Factor

Table 5–8 Configure robustness factor

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  After configuring the robustness factor, the following parameters also change with the robustness parameters:
• Group member timeout = Robustness factor * general group query time + maximum response time;
• Other querier timeout = Robustness factor * general query time + maximum response time/2;
• The larger the robustness factor, the larger the IGMP group member timeout and other querier timeout. The user sets the value according to the actuality of the network.

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Configure Maximum Response Time

The general group query packet sent by the IGMPv2 querier contains the maximum response time field and the receiver sends the group member relation report within the maximum response interval.

Table 5–9 Configure the maximum response time

Configure Specified Group Query

After the IGMP querier receives the leave packet of one multicast group, send the specified group query packets of the “specified group query times” times to query the multicast group on the segment, so as to know whether the subnet has the members of the multicast group. If not receiving the member relation report of the multicast group after waiting for “last life period”, delete the information of the multicast group.

Table 5–10 Configure the specified group query

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  ip igmp last-member-query-interval and ip igmp last-member-query-count are invalid in IGMPv1, because the IGMPv1 host does not send leave packets when leaving one multicast group.

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Configure Other Querier Timeout

The device with the smallest address in one subnet is elected as the querier and the other devices are called non-querier. On the non-queriers, set one timeout as the timer of “other querier timeout” (the other queriers have timer) for the querier. When the non-querier receives the query packet of the querier, refresh the timer. When the timer times out, it indicates that the current IGMP querier becomes invalid and you need to re-elect the new querier.

Table 5–11 Configure the other querier timeout

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  If the configure other querier timeout is smaller than the query interval, the querier in the network may change repeatedly.

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Configure Fast Leave

The end segment in the network only connects to one host to perform the switching action of the multicast group frequently. To reduce the leave delay, you can configure the fast leave of the multicast group on the device.

After configuring the fast leave, the device receives the leave packet of one multicast group and checks whether the multicast group belongs to the fast leave range. If yes, the device does not send the specified group query packet to the segment any more and deletes the information of the multicast group immediately.

Table 5–12 Configure the fast leave