In IPv4 multicast group membership is managed through Internet Group Management Protocol (IGMP).Internet Group Management Protocol (IGMP) is a protocol that manages host membership in IP multicast group. A specific host listens on a specific IP multicast address and receives all packets to that IP address. In IPv6, multicast group management is accomplished with a set of ICMPv6 messages that comprise the Multicast Listener Discovery (MLD) protocol.
MLD Basic Overview:
MLDv1 is similar to IGMPv2 and MLDv2 similar to IGMPv3.Like IGMP, MLDv2 is backward compatible to MLDv1.For cisco switches, MLD snooping provides the same functionality as IGMP snooping in IPv4.It provides information to the switch about which connected hosts are member of a specific group so that switch can make decision about whether, and on which interface, to allow traffic for that group.
MLD is automatically enabled when you perform one of the following configuration tasks on an interface:
•Statically bind a local multicast group
•Enable link-local group reports
MLD uses three different types of messages:
1) Multicast Listener Query: The Query message type has two subtypes.
->The General Query issued by routers to discover the entire multicast groups that listeners on the link are subscribed to.
-> Multicast-Address-Speciﬁc Query: issued by routers to discover whether there are any local link subscribers (listeners) to a particular multicast address. Only routers send queries, and usually there is only one router that acts as a querier on each link.
2) Multicast Listener Report: An unsolicited Report message is sent by any node when it begins listening to a multicast address; Report messages are generated in response to a Query message sent by a router(either a query for a speciﬁc multicast address or a general query).
3) Multicast Done: In a done message, the multicast address field is that of the specific IPv6 multicast address to which the source of the MLD message is no longer listening.
The figure below shows where MLD operate within the IPv6 multicast environment.
A) Configuring MLD Snooping:
To enable MLD snooping globally, perform this task:
Router(config)# ipv6 mld snooping
Router# show ipv6 mld interface vlan 100 | include globally
MLD snooping is globally enabled
To enable MLD snooping in a VLAN, perform this task:
Router# interface vlan 125
Router(config-if)# ipv6 mld snooping
Router# show ipv6 mld interface vlan 125 | include snooping
MLD snooping is globally enabled
MLD snooping is enabled on this interface
MLD snooping fast-leave is enabled and querier is enabled
MLD snooping explicit-tracking is enabled
MLD snooping last member query response interval is 1000 ms
MLD snooping report-suppression is disabled
B) Configures MLD reporting for a specified group and source.
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