H3C Technologies H3C WX6000 Series Access Controllers - Manual (Page 321)

29-3
Aging timers for dynamic ports in IGMP Snooping and related messages and actions
Table 29-1 Aging timers for dynamic ports in IGMP Snooping and related messages and actions
Timer Description Message before expiry Action after expiry
Router port aging timer
For each router port, the
switch sets a timer
initialized to the aging
time of the route port.
IGMP general query of
which the source address
is not 0.0.0.0 or PIM hello The switch removes this
port from its router port
list.
Member port aging timer
When a port joins a
multicast group, the
switch sets a timer for the
port, which is initialized to
the member port aging
time.
IGMP membership report
The switch removes this
port from the multicast
group forwarding table.
The port aging mechanism of IGMP Snooping works only for dynamic ports; a static port will never age
out.
Work Mechanism of IGMP Snooping
A switch running IGMP Snooping performs different actions when it receives different IGMP messages,
as follows:
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 router port existing in its router port list, the switch resets the aging timer of
this router port.
z
If the receiving port is not a router port existing in its router port list, the switch adds it into its router
port list and sets an aging timer for this router port.
When receiving a membership report
A host sends an IGMP report to the multicast router 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 multicast router 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 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 member port to the outgoing port list, and starts
a member port aging timer for that port.