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Configuring IPv6 MLD Snooping
Information About MLD Snooping
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 is 2.
Multicast Router Discovery
Like IGMP snooping, MLD snooping performs multicast router 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 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. 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.
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