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Configuring IPv6 MLD Snooping
Prerequisites
MLD Done Messages and Immediate-Leave
When the Immediate-Leave feature is enabled and a host sends an MLDv1 Done message (equivalent to an IGMP leave
message), the port on which the Done message was received is immediately deleted from the group.You enable
Immediate-Leave on VLANs and (as with IGMP snooping), you should only use the feature on VLANs where a single host
is connected to the port. If the port was the last member of a group, the group is also deleted, and the leave information
is forwarded to the detected IPv6 multicast routers.
When Immediate Leave is not enabled in a VLAN (which would be the case when there are multiple clients for a group
on the same port) and a Done message is received on a port, an MASQ is generated on that port. The user can control
when a port membership is removed for an existing address in terms of the number of MASQs. A port is removed from
membership to an address when there are no MLDv1 reports to the address on the port for the configured number of
queries.
The number of MASQs generated is configured by using the ipv6 mld snooping last-listener-query count global
configuration command. The default number is 2.
The MASQ is sent to the IPv6 multicast address for which the Done message was sent. If there are no reports sent to
the IPv6 multicast address specified in the MASQ during the switch maximum response time, the port on which the
MASQ was sent is deleted from the IPv6 multicast address database. The maximum response time is the time configured
by using the ipv6 mld snooping last-listener-query-interval global configuration command. If the deleted port is the
last member of the multicast address, the multicast address is also deleted, and the switch sends the address leave
information to all detected multicast routers.
Topology Change Notification Processing
When topology change notification (TCN) solicitation is enabled by using the ipv6 mld snooping tcn query solicit global
configuration command, MLDv1 snooping sets the VLAN to flood all IPv6 multicast traffic with a configured number of
MLDv1 queries before it begins sending multicast data only to selected ports. You set this value by using the ipv6 mld
snooping tcn flood query count global configuration command. The default is to send two queries. The switch also
generates MLDv1 global Done messages with valid link-local IPv6 source addresses when the switch becomes the STP
root in the VLAN or when it is configured by the user. This is same as done in IGMP snooping.
Prerequisites
Review the
Information About MLD Snooping, page
Guidelines and Limitations
You can configure MLD snooping characteristics at any time, but you must globally enable MLD snooping by using
the ipv6 mld snooping global configuration command for the configuration to take effect.
When the IPv6 multicast router is a Catalyst 6500 switch and you are using extended VLANs (in the range 1006 to
4094), IPv6 MLD snooping must be enabled on the extended VLAN on the Catalyst 6500 switch in order for this
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 Catalyst 6500 switch.
MLD snooping and IGMP snooping act independently of each other. You can enable both features at the same time
on the switch.
The maximum number of multicast entries allowed on the switch is determined by the configured SDM template.
The maximum number of address entries allowed for the switch is 1000.
753.
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