H3C Technologies H3C S10500 Series Switches - Manual (Page 31)

16
Aging timers for dynamic ports in IGMP snooping and related messages and actions
Timer Description Message before expiry Action after expiry
Dynamic router port
aging timer
For each dynamic router
port, the switch sets a
timer initialized to the
dynamic router port
aging time.
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.
Dynamic member port
aging timer
When a port dynamically
joins a multicast group,
the switch sets a timer for
the port, which is
initialized to the dynamic
member port aging time.
IGMP membership report
The switch removes this
port from the IGMP
snooping forwarding
table.
NOTE:
The port aging mechanism of IGMP snooping works only for dynamic ports; a static port will never age
out.
How IGMP snooping works
A switch that runs IGMP snooping performs different actions when it receives different IGMP messages.
CAUTION:
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 more information, 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 determine whether active multicast group members exist on the subnet.
After receiving an IGMP general query, the switch forwards it through all ports in the VLAN (except the
port that received the query). The switch performs the following judgment:
• If the port that received the query is a dynamic router port that exists in its router port list, the switch
resets the aging timer for this dynamic router port.
• If the port is not a dynamic router port that exists 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:
• After receiving an IGMP query, a multicast group member host responds with an IGMP report.
• 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.
After receiving an IGMP report, the switch forwards it through all the router ports in the VLAN, resolves
the address of the reported multicast group. The switch also performs the following judgment: