Protocols And Standards; Recommended Configuration Procedure - HP 1920 Gigabit Ethernet Switch Series User Manual

switch cannot determine whether the reported multicast group still has active members attached to that
port.
Leave message
An IGMPv1 host silently leaves a multicast group and the switch is not notified of the leaving. However,
because the host stops sending IGMP reports as soon as it leaves the multicast group, the switch removes
the port that connects to the host from the forwarding entry for the multicast group when the aging timer
for the port expires.
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 message on a dynamic member port, the switch first examines
whether a forwarding entry matches the group address in the message, and, if a match is found, 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
•
port, the switch directly discards the IGMP leave message.
If a forwarding entry matches the group address and the forwarding entry contains the port, the
•
switch forwards the leave 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, it restarts
the aging timer for the 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 the 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 of the 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 an IGMP report in response to the
•
group-specific query before its aging timer expires, it means that some host attached to the port is
receiving or expecting to receive multicast data for the multicast group. The switch restarts the aging
timer for the port.
If the port receives no IGMP report in response to the group-specific query before its aging timer
•
expires, it means 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
Remarks
Required.
Disabled by default.
255