SMC Networks SMC6724L3 manual 145, Configuring Igmp Interface Parameters

MULTICAST FILTERING

Configuring IGMP Interface Parameters

This switch uses IGMP (Internet Group Management Protocol) to query for any attached hosts that want to receive a specific multicast service. The hosts may respond with several types of IP multicast messages. Hosts respond to queries with report messages that indicate which groups they want to join or the groups to which they already belong. If a router does not receive a report message within a specified period of time, it will prune that interface from the multicast tree. A host can also submit a join message at any time without waiting for a query from the router. Host can also signal when they no longer want to receive traffic for a specific group by sending a leave-group message.

These IGMP messages are used by the router to identify ports containing multicast hosts and to restrict the downstream flow of multicast data to only these ports. If more than one router on the LAN is performing IP multicasting, one of these is elected as the “querier” and assumes the role of querying for group members. It then propagates the service request up to any neighboring multicast router to ensure that it will continue to receive the multicast service. The following parameters are used to control Layer 3 IGMP and query functions.

Command Attributes

•VLAN (Interface) – VLAN interface bound to a primary IP address. (Range: 1-4094)

•IGMP Protocol Status (Admin Status) – Enables IGMP on a VLAN interface. (Default: Disabled)

•Last Member Query Interval – A multicast client sends an IGMP leave message when it leaves a group. The router then checks to see if this was the last host in the group by sending an IGMP query and starting a timer based on this command. If no reports are received before the timer expires, the group is deleted. (Range: 0-25 seconds; Default: 1 second)

-This value may be tuned to modify the leave latency of the network. A reduced value results in reduced time to detect the loss of the last member of a group.

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