3Com S7906E - Switch, Configuration Manual

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How IGMP Snooping Works
A switch running IGMP snooping performs different actions when it receives different IGMP messages,
as follows:
The description about adding or deleting a port in this section is only for a dynamic port. Static ports can
be added or deleted only through the corresponding configurations. For details, see Configuring Static
Ports .
When receiving a general query
The IGMP querier periodically sends IGMP general queries to all hosts and routers (224.0.0.1) on the
local subnet to find out whether active multicast group members exist on the subnet.
Upon receiving an IGMP general query, the switch forwards it through all ports in the VLAN except the
receiving port and performs the following to the receiving port:
z
If the receiving port is a dynamic router port existing in its router port list, the switch resets the aging
timer of this dynamic router port.
z
If the receiving port is not a dynamic router port existing in its router port list, the switch adds it into
its router port list and sets an aging timer for this dynamic router port.
When receiving a membership report
A host sends an IGMP report to the IGMP querier in the following circumstances:
z
Upon receiving an IGMP query, a multicast group member host responds with an IGMP report.
z
When intended to join a multicast group, a host sends an IGMP report to the IGMP querier to
announce that it is interested in the multicast information addressed to that group.
Upon receiving an IGMP report, the switch forwards it through all the router ports in the VLAN, resolves
the address of the reported multicast group, and performs the following:
z
If no forwarding table entry exists for the reported group, the switch creates an entry, adds the port
as a dynamic member port to the outgoing port list, and starts a member port aging timer for that
port.
z
If a forwarding table entry exists for the reported group, but the port is not included in the outgoing
port list for that group, the switch adds the port as a dynamic member port to the outgoing port list,
and starts an aging timer for that port.
z
If a forwarding table entry exists for the reported group and the port is included in the outgoing port
list, which means that this port is already a dynamic member port, the switch resets the aging timer
for that port.