3Com Switch 4800G 24-Port Configuration Manual page 581

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How MLD Snooping
Works
switch registers all its local router ports (including static and dynamic router
ports) in its router port list.
Member port: A member port (also known as IPv6 multicast group member
■
port) is a port on the Ethernet switch that leads switch towards multicast group
members. In the figure, Ethernet 1/0/2 and Ethernet 1/0/3 of Switch A and
Ethernet 1/0/2 of Switch B are member ports. The switch registers all the
member ports (including static and dynamic member ports) on the local device
in its MLD Snooping forwarding table.
Whenever mentioned in this document, a router port is a router-connecting
■
port on the switch, rather than a port on a router.
On an MLD-snooping-enabled switch, the ports that received MLD general
■
queries with the source address other than 0::0 or IPv6 PIM hello messages are
router ports.
Aging timers for dynamic ports in MLD Snooping
Table 56 Aging timers for dynamic ports in MLD Snooping and related messages and
actions
Timer Description
Router port aging For each router port,
timer the switch sets a timer
initialized to the aging
time of the route port.
Member port aging When a port joins an
timer IPv6 multicast group,
the switch sets a timer
for the port, which is
initialized to the
member port aging
time.
The port aging mechanism of MLD Snooping works only for dynamic ports; a
static port will never age out.
A switch running MLD Snooping performs different actions when it receives
different MLD messages, as follows:
General queries
The MLD querier periodically sends MLD general queries to all hosts and routers
(FF02::1) on the local subnet to find out whether IPv6 multicast group members
exist on the subnet.
Upon receiving an MLD general query, the switch forwards it through all ports in
the VLAN except the receiving port and performs the following to the receiving
port:
If the receiving port is a router port existing in its router port list, the switch
■
resets the aging timer of this router port.
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.
MLD Snooping Overview
Message before
expiry Action after expiry
MLD general query of The switch removes
which the source this port from its
address is not 0::0 or router port list.
IPv6 PIM hello.
MLD report message. The switch removes
this port from the IPv6
multicast group
forwarding table.
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