52
Timer Description
Message before
expiry
Action after expiry
aging timer
port, the switch sets a
timer initialized to the
dynamic router port aging
time.
which the source
address is not 0::0 or
IPv6 PIM hello.
port from its router port
list.
Dynamic member port
aging timer
When a port dynamically
joins an IPv6 multicast
group, the switch sets a
timer for the port, which is
initialized to the dynamic
member port aging time.
MLD report message.
The switch removes this
port from the MLD
snooping forwarding
table.
NOTE:
The port aging mechanism of MLD snooping works only for dynamic ports; a static port will never
age out.
How MLD snooping works
A switch that is running MLD snooping performs different actions when it receives different MLD
messages.
NOTE:
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
"
."
General queries
The MLD querier periodically sends MLD general queries to all hosts and routers—FF02::1—on the
local subnet to determine whether IPv6 multicast group members exist on the subnet.
After receiving an MLD general query, the switch forwards it through all ports in the VLAN except the
port that received the MLD query. The switch performs the following judgment:
•
If the port that received the MLD query is a dynamic router port in its router port list, the switch
resets the aging timer for this dynamic router port.
•
If the port is not included in its router port list, the switch adds it into its router port list as a
dynamic router port and sets an aging timer for it.
Membership reports
A host sends an MLD report to the MLD querier in the following circumstances:
•
If the host has been a member of an IPv6 multicast group, after receiving an MLD query, the
host responds with an MLD report.
•
If the host wants to join an IPv6 multicast group, the host sends an MLD report to the MLD
querier to announce that it is interested in the multicast information addressed to that IPv6
multicast group.
After receiving an MLD report, the switch forwards it through all the router ports in the VLAN,
resolves the address of the reported IPv6 multicast group, and performs the following to the
receiving port:
•
If no forwarding table entry exists for the reported IPv6 multicast 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.