31.3.4 IGMP querier function

The IGMP querier functionality is used by the Switch to send IGMP Query messages by proxy to recipient hosts on environments where no multicast router exists in the VLAN, and only hosts that send and receive multicast packets exist. Multicast routers regularly send IGMP Query messages and then check for reception from hosts to determine whether group members exist. If no multicast router exists, group members can no longer be monitored because no response is received from recipient hosts. This functionality enables the IGMP snooping functionality even when no multicast routers exist in the VLAN. The Switch sends an IGMP Query message every 125 seconds.

Notes

When operating in IGMPv2, Query Interval must be 125 seconds for the applicable VLAN.

In order to use the IGMP querier functionality, an IP address must be set for VLANs using the IGMP snooping functionality.

When devices sending IGMP Query messages exist in a VLAN, the IGMP Query message transmission source with the lowest IP address becomes the representative querier, and it sends IGMP Query messages. If another device in the VLAN is the representative querier, the Switch stops using the IGMP querier functionality to send Query messages.

If the representative querier stops, such as due to a malfunction, a new representative querier is chosen. When the Switch is determined to be the representative querier, such as due to a malfunction on another device in the VLAN, IGMP Query message transmission is started. In the Switch, the monitoring period for the representative querier follows Other Querier Present Interval.

Notes

Other Querier Present Interval is calculated as Robustness Variable(RV)NGQuery Interval(QI)+Query Response Interval(QRI)/2.

RV,QI,QRI is shown below.

• When another device is operating in IGMPv3 with a representative querier

  RV,QI = retrieve from received Query messaging

  QRI=10 seconds

• When the Switch operates in IGMPv3 with a representative querier or in IGMPv2

  RV=2

  QI=125 seconds

  QRI=10 seconds

By default, the version for IGMP Queries sent by the Switch is IGMPv2. After the Switch is running, the IGMP Query version follows the IGMP version of the representative querier.