User guide

IGMP snooping Functional Overview (Includes New Functionality) IGMP snooping
3-7
iMG/RG Software Reference Manual (IGMP)
Instead, if the received IGMP report message refers to a multicast channel that is already registered in the local
database, the IGMP process will drop it without forwarding it to the multicast router and will update the local
database, if needed.
Periodically the multicast router sends Generic Queries to check the presence of active multicast hosts.
Then the IGMP process answers to each IGMP query notifying all the multicast stream registered on the local
multicast group database without querying the internal hosts.
The upper multicast router does not have therefore any knowledge of the internal lan configuration. IGMP
reports (and leaves) messages are always sent by the CPE IGMP process using the Residential Gateway IP and
MAC source address.
In order to keep the local multicast group database up to date, the IGMP process sends periodically IGMP
generic queries to the internal hosts. The period IGMP queries are sent, is called Query Interval. Each host still
interested to receive multicast streams must respond with one or more IGMP Report messages within a time-
frame called Query Response Interval.
The picture here below shows an example scenario where two hosts join two different multicast channels.