Users Guide
Figure 13. IGMP Membership Reports: Joining and Filtering
Leaving and Staying in Groups
The below illustration shows how multicast routers track and refreshes the state change in response to group-and-specic and general
queries.
• Host 1 sends a message indicating it is leaving group 224.1.1.1 and that the included lter for 10.11.1.1 and 10.11.1.2 are no longer necessary.
• The querier, before making any state changes, sends a group-and-source query to see if any other host is interested in these two
sources; queries for state-changes are retransmitted multiple times. If any are interested, they respond with their current state
information and the querier refreshes the relevant state information.
• Separately in the below gure, the querier sends a general query to 224.0.0.1.
• Host 2 responds to the periodic general query so the querier refreshes the state information for that group.
Figure 14. IGMP Membership Queries: Leaving and Staying in Groups
IGMP Snooping
IGMP snooping is auto-congured on an Aggregator.
Multicast packets are addressed with multicast MAC addresses, which represents a group of devices rather than one unique device.
Switches forward multicast frames out of all ports in a VLAN by default, even if there are only a small number of interested hosts, resulting
Internet Group Management Protocol (IGMP)
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