24-2
Cisco Catalyst Switch Module 3110 and 3012 for IBM BladeCenter Software Configuration Guide
OL-12189-01
Chapter 24 Configuring IPv6 MLD Snooping
Understanding MLD Snooping
Version 1 (MLDv1) is equivalent to IGMPv2, and MLD Version 2 (MLDv2) is equivalent to 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:
• 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.
The switch can snoop on both MLDv1 and MLDv2 protocol packets and bridge IPv6 multicast data
based on destination IPv6 multicast addresses.
Note The switch does not support MLDv2 enhanced snooping (MESS), which sets up IPv6 source and
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 Catalyst Switch Module 3110 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.
On the Catalyst Switch Module 3110, 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:
• MLD Messages, page 24-2
• MLD Queries, page 24-3
• Multicast Client Aging Robustness, page 24-3
• Multicast Router Discovery, page 24-4
• MLD Reports, page 24-4
• MLD Done Messages and Immediate-Leave, page 24-4
• Topology Change Notification Processing, page 24-5
• MLD Snooping in Switch Stacks, page 24-5
MLD Messages
MLDv1 supports three types of messages:
• 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.
