Protocols And Standards; Recommended Configuration Procedure - HP 1910 User Manual

An IGMPv2 or IGMPv3 host sends an IGMP leave message to the multicast router when it leaves a
multicast group.
When the switch receives an IGMP leave group message on a member port, the switch first examines
whether a forwarding entry matches the group address in the message, and, if a match is found,
determines whether the forwarding entry for the group contains the dynamic member port.
If no forwarding entry matches the group address, or if the forwarding entry does not contain the
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port, the switch directly discards the IGMP leave group message.
If a forwarding entry matches the group address and the forwarding entry contains the port, the
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switch forwards the IGMP leave group message to all router ports in the VLAN. Because the switch
does not know whether any other hosts attached to the port are still listening to that group address,
the switch does not immediately remove the port from the forwarding entry for that group. Instead,
the switch resets the aging timer for that port.
After receiving the IGMP leave message, the IGMP querier resolves the multicast group address in the
message and sends an IGMP group-specific query to that multicast group through the port that received
the leave message. After receiving the IGMP group-specific query, the switch forwards it through all its
router ports in the VLAN and all member ports for that multicast group. The switch also performs one of
the following actions for the port that received the IGMP leave message:
If the port (assuming that it is a dynamic member port) receives any IGMP report in response to the
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group-specific query before its aging timer expires, it indicates that some host attached to the port
is receiving or expecting to receive multicast data for that multicast group. The switch resets the
aging timer of the port.
If the port receives no IGMP report in response to the group-specific query before its aging timer
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expires, it indicates that no hosts attached to the port are still listening to that group address. The
switch removes the port from the forwarding entry for the multicast group when the aging timer
expires.

Protocols and standards

RFC 4541, Considerations for Internet Group Management Protocol (IGMP) and Multicast Listener
Discovery (MLD) Snooping Switches

Recommended configuration procedure

Step
1. Enabling IGMP snooping
globally
2. Configuring IGMP snooping
in a VLAN
Remarks
Required.
Disabled by default.
Required.
Enable IGMP snooping for the VLAN and configure the IGMP snooping
version and querier.
By default, IGMP snooping is disabled in a VLAN.
IMPORTANT:
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Enable IGMP snooping globally before you enable it for a VLAN.
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IGMP snooping for a VLAN takes effect only on the member ports in
that VLAN.
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