32.3.4 IGMP querier function

IGMP querier functionality allows the Switch to send IGMP Query messages to the receiving host on behalf of the Switch in an environment where there is no multicast router in VLAN and only the sending and receiving hosts of multicast packets. 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 IGMP Query messages at the interval specified in the configuration command ip igmp snooping query-interval.

Notes

When operating in IGMPv2, Query Interval must be the same for the applicable VLAN. If Query interval of the representative querier is 10 seconds or less, design a networkthat satisfies the following conditions:

• Number of simultaneous connections of IPv4 multicast receivers connected under the Switch/Query interval (seconds) = 100 or less

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. 0. The seconds part is rounded up to one second.

RV,QI,QRI is shown below.

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

RV,QI,QRI = retrieve from last received Query messagemessage

.When another device is operating in IGMPv2 with a representative querier

RV=2

QI = Duration specified by the configuration command ip igmp snooping query-interval (defaults to 125 seconds)

10 seconds when QRI=QI is 11 seconds or more, and (QI-1) seconds when QI is 10 seconds or less

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. Membership Query messages sent by the Switch are set as follows.

• IGMPv1/IGMPv2

  Max Resp Code = 100 when QI # of the Switch is 11 seconds or more, and (QI-1) seconds NG 10 when it is 10 seconds or less. However, 9 if QI is 1 second.

• IGMPv3

  Max Resp Code = 100 when QI # of the Switch is 11 seconds or more, and (QI-1) seconds NG 10 when it is 10 seconds or less. However, 9 if QI is 1 second.

  QRV=2

  QQIC = QI,128 of the Switch or more: Rounded up by floating-point operation.

#

QI of the Switch = Duration specified by the configuration command ip igmp snooping query-interval (defaults to 125 seconds)