3Com Switch 8800 Advanced Software V5 Configuration Guide

MLD Snooping Overview 651
■ Member port: A member port (also known as IPv6 multicast group member
port or Listener Port) is a port on a Layer 2 switch that leads the switch to an
IPv6 multicast group member. In the figure, Ethernet 1/1/1 and Ethernet 1/1/2
of Switch A and Ethernet1/1/1 of Switch B are member ports. The switch
records all member ports on the local device in the MLD Snooping forwarding
table.
n
■ Whenever mentioned in this document, a router port is a router-side port on a
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. For details about IPv6 PIM hello messages, see
“Configuring IPv6
PIM Hello Options” on page 693.
Port aging timers in MLD Snooping
Work Mechanism of
MLD Snooping
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
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.
Membership reports
A host sends an MLD report to the multicast router in the following circumstances:
Tab le 30 Port aging timers in MLD 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
MLD general query
of which the source
address is not 0::0
or IPv6 PIM hello
The switch removes this port
from its router port list
Member port aging
timer
When a port joins
an IPv6 multicast
group, the switch
sets a timer for the
port, which is
initialized to the
member port aging
time
MLD report
message
The switch removes this port
from the IPv6 multicast
group forwarding table