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Understanding MLD Snooping
IGMPv3. MLD is a subprotocol of Internet Control Message Protocol Version 6 (ICMPv6), and MLD
messages are a subset of ICMPv6 messages, identified in IPv6 packets by a preceding Next Header value
of 58.
The switch supports two versions of MLD snooping:
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The switch can snoop on both MLDv1 and MLDv2 protocol packets and bridge IPv6 multicast data
based on destination IPv6 multicast addresses.
The switch does not support MLDv2 enhanced snooping (MESS), which sets up IPv6 source and
Note
destination multicast address-based forwarding.
MLD snooping can be enabled or disabled globally or per VLAN. When MLD snooping is enabled, a
per-VLAN IPv6 multicast MAC address table is constructed in software and a per-VLAN IPv6 multicast
address table is constructed in software and hardware. The switch then performs IPv6 multicast-address
based bridging in hardware.
According to IPv6 multicast standards, the switch derives the MAC multicast address by performing a
logical-OR of the four low-order octets of the switch MAC address with the MAC address of
33:33:00:00:00:00. For example, the IPv6 MAC address of FF02:DEAD:BEEF:1:3 maps to the Ethernet
MAC address of 33:33:00:01:00:03.
A multicast packet is unmatched when the destination IPv6 address does not match the destination MAC
address. The switch forwards the unmatched packet in hardware based the MAC address table. If the
destination MAC address is not in the MAC address table, the switch floods the packet to all ports in the
same VLAN as the receiving port.
These sections describe some parameters of IPv6 MLD snooping:
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MLD Messages
MLDv1 supports three types of messages:
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Cisco Catalyst Blade Switch 3130 and 3032 for Dell Software Configuration Guide
25-2
MLDv1 snooping detects MLDv1 control packets and sets up traffic bridging based on IPv6
destination multicast addresses.
MLDv2 basic snooping (MBSS) uses MLDv2 control packets to set up traffic forwarding based on
IPv6 destination multicast addresses.
MLD Messages, page 25-2
MLD Queries, page 25-3
Multicast Client Aging Robustness, page 25-3
Multicast Router Discovery, page 25-3
MLD Reports, page 25-4
MLD Done Messages and Immediate-Leave, page 25-4
Topology Change Notification Processing, page 25-5
MLD Snooping in Switch Stacks, page 25-5
Listener Queries are the equivalent of IGMPv2 queries and are either General Queries or
Multicast-Address-Specific Queries (MASQs).
Multicast Listener Reports are the equivalent of IGMPv2 reports
Multicast Listener Done messages are the equivalent of IGMPv2 leave messages.
Chapter 25
Configuring IPv6 MLD Snooping
OL-12247-04
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