Mld Reports - Cisco Catalyst 2960 series Configuration Manual

Information About Configuring IPv6 MLD Snooping
• 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 or forwarded from the switch. When IPv6 multicast
routers are detected and an MLDv1 report is received, an IPv6 multicast group address is 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 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 (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.
Consolidated Platform Configuration Guide, Cisco IOS Release 15.2(4)E (Catalyst 2960-X Switches)
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