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Catalyst 3750 SwitchSoftware Configuration Guide
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Configuring IPv6 MLD Snooping
You can use Multicast Listener Discovery (MLD) snooping to enable efficient distribution of IP
version6 (IPv6) multicast data to clients and routers in a switched network on the Catalyst3750 switch.
Unless otherwise noted, the term switch refers to a standalone switch and to a switch stack.
Note To use IPv6, you must configure the dual IPv4 and IPv6 Switch Database Management (SDM) template
on the switch. You select the template by entering the sdm prefer dual-ipv4-and-ipv6 {default | vlan}
[desktop] global configuration command.
For related information, see these chapters:
For more information about SDM templates, see Chapter8, “Configuring SDM Templates.”
For information about IPv6 on the switch, see Chapter39, “Configuring IPv6 Uni cast Routing.”
Note For complete syntax and usage information for the commands used in this chapter, see the command
reference for this release or the Cisco IOS documentation referenced in the procedures.
This chapter includes these sections:
“Understanding MLD Snooping” section on page40-1
“Configuring IPv6 MLD Snooping” section on page 40-5
“Displaying MLD Snooping Information” section on page40-12

Understanding MLD Snooping

In IP version 4 (IPv4), Layer 2 switches can use Internet Group Management Protocol (IGMP) snooping
to limit the flooding of multicast traffic by dynamically configuring Layer2 interfaces so that multicast
traffic is forwarded to only those interfaces associated with IP multicast devices. In IPv6, MLD snooping
performs a similar function. With MLD snooping, IPv6 multicast data is selectively forwarded to a list
of ports that want to receive the data, instead of being flooded to all ports in a VLAN. This list is
constructed by snooping IPv6 multicast control packets.
MLD is a protocol used by IPv6 multicast routers to discover the presence of multicast listeners (nodes
wishing to receive IPv6 multicast packets) on its directly attached links and to discover which multicast
packets are of interest to neighboring nodes. MLD is derived from IGMP; MLD version 1 (MLDv1) is