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Cisco IE 2000 Switch Software Configuration Guide
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Chapter 44 Configuring IPv6 MLD Snooping
Information About Configuring IPv6 MLD Snooping
Note When the IPv6 multicast router is a Catalyst 6500 switch and you are using extended VLANs (in the
range 1006 to 4096), IPv6 MLD snooping must be enabled on the extended VLAN on the Catalyst 6500
switch in order for the switch to receive queries on the VLAN. For normal -range VLANs (1 to 1005), it
is not necessary to enable IPv6 MLD snooping on the VLAN on the C atalyst 6500 switch.
When a group exists in the MLD snooping database, the switch responds to a group-specific query by
sending an MLDv1 report. When the group is unknown, the group-specific query is flooded to the
ingress VLAN.
When a host wants to leave a multicast group, it can send out an MLD Done message (equivalent to
IGMP Leave message). When the switch receives an MLDv1 Done message, if Immediate-Leave is not
enabled, the switch sends an MASQ to the port from which the message was received to determine if
other devices connected to the port should remain in the multicast group.
Multicast Client Aging Robustness
You can configure port membership removal from addresses based on the number of queries. A port is
removed from membership to an address only when there are no reports to the address on the port for
the configured number of queries. The default number i s 2.
Multicast Router Discovery
Like IGMP snooping, MLD snooping performs multicast route r discovery, with these characteristics:
• Ports configured by a user never age out.
• Dynamic port learning results from MLDv1 snooping queries and IPv6 PIMv2 packets.
• If there are multiple routers on the same Layer 2 interface, MLD snooping tracks a single multicast
router on the port (the router that most recently sent a router control packet).
• Dynamic multicast router port aging is based on a default timer of 5 minutes; the multicast router is
deleted from the router port list if no control packet is received on the port for 5 minutes.
• IPv6 multicast router discovery only takes place when MLD snooping is enabled on the switch.
• Received IPv6 multicast router control packets are always flooded to the ingress VLAN, whether or
not MLD snooping is enabled on the switch.
• After the discovery of the first IPv6 multicast router port, unknown IPv6 multicast data is forwarded
only to the discovered router ports (before that time, all IPv6 multicast data is flooded to the ingress
VLAN).
MLD Reports
The processing of MLDv1 join messages is essentially the same as with IGMPv2. When no IPv6
multicast routers are detected in a VLAN, reports are not processed o r forwarded from the switch. When
IPv6 multicast routers are detected and an MLDv1 report is received, an IPv6 multicast group address
and an IPv6 multicast MAC address are entered in the VLAN MLD database. Then all IPv6 multicast
traffic to the group within the VLAN is forwarded using this address. When MLD snooping i s disabled,
reports are flooded in the ingress VLAN.