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Catalyst 4500 Series Switch, Cisco IOS Software Configuration Guide - Cisco IOS XE 3.9.xE and IOS 15.2(5)Ex
Chapter 29 Configuring IPv6 Multicast Listener Discovery Snooping
About MLD Snooping
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 or 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. All IPv6 multicast traffic
to the group within the VLAN is then forwarded using this address. When MLD snooping is disabled,
reports are flooded in the ingress VLAN.
When MLD snooping is enabled, MLD report suppression, called listener message suppression, is
automatically enabled. With report suppression, the switch forwards the first MLDv1 report received by
a group to IPv6 multicast routers; subsequent reports for the group are not sent to the routers. When
MLD snooping is disabled, report suppression is disabled, and all MLDv1 reports are flooded to the
ingress VLAN.
The switch also supports MLDv1 proxy reporting. When an MLDv1 MASQ is received, the switch
responds with MLDv1 reports for the address on which the query arrived if the group exists in the switch
on another port and if the port on which the query arrived is not the last member port for the address.
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 (the case when multiple clients for a group exist 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 no reports are
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
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