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XG2000 series User's Guide
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All Rights Reserved, Copyright (C) PFU LIMITED 2009
4.9.4 IGMP Querier
In a typical network configuration, the multicast router periodically sends out an IGMP General Query message to determine if
any of the hosts on the network are members of any multicast groups. Receiving a response from a host ascertains its
membership in a multicast group.
IGMP Querier is a function that acts as a proxy for a multicast router when one is not available in a network segment to send
an IGMP General Query message to all hosts.
The frequency of Query messages issued is configured using the "ip snooping vlan send-query-count" command.
The frequency of the General Query messages sent (query interval) are automatically calculated by the following equation
based on the send query count and the group membership interval.
z Query interval = (Group membership interval - 10)/send query count (seconds)
The default setting for the Query interval is 125 seconds.
Upon reception of an IGMP Leave message, the device sends an IGMP Specific Query (GSQ) message to determine that the
host is interested in leaving the group.
If an IGMP Specific Query message is sent as many times as specified by the send query count and the host does not respond
with an IGMP Report message, that host is removed.
z Generally, IGMP Querier uses "0.0.0.0" for the source IP address when sending a Query message.
Since some client software does not return a response for a Query message with the source IP
address being set to "0.0.0.0", it is recommended that an address other than "0.0.0.0" be used.
z If a multicast router exists on the network segment, the device does not send Query message even if
IGMP Querier is valid.