Note As per RFC 4291 , the FF0x::/12 (where the T flag is set to 0 in IPv6 destination address) is for permanently assigned (“well-known”) IPv6 multicast address range. In Cisco Catalyst 9300 Series Switches, the default behavior for packets with this address range is to flood in the ingress VLAN. Membership in a multicast group is dynamic; hosts can join and leave at any time. There is no restriction on the location or number of members in a multicast group. A host can be a member of more than one multicast group at a time. How active a multicast group is, its duration, and its membership can vary from group to group and from time to time. A group that has members may have no activity.
IPv6 Multicast Routing Implementation The Cisco IOS software supports the following protocols to implement IPv6 multicast routing: • MLD is used by IPv6 switches to discover multicast listeners (nodes that want to receive multicast packets destined for specific multicast addresses) on directly attached links. There are two versions of MLD: MLD version 1 is based on version 2 of the Internet Group Management Protocol (IGMP) for IPv4, and MLD version 2 is based on version 3 of the IGMP for IPv4. IPv6 multicast for Cisco IOS software uses both MLD version 2 and MLD version 1. MLD version 2 is fully backward-compatible with MLD version 1 (described in RFC 2710).
Hosts that support only MLD version 1 will interoperate with a switch running MLD version 2. Mixed LANs with both MLD version 1 and MLD version 2 hosts are likewise supported. • PIM-SM is used between switches so that they can track which multicast packets to forward to each other and to their directly connected LANs. • PIM in Source Specific Multicast (PIM-SSM) is similar to PIM-SM with the additional ability to report interest in receiving packets from specific source addresses (or from all but the specific source addresses) to an IP multicast address.
IPv6 Multicast Listener Discovery Protocol To start implementing multicasting in the campus network, users must first define who receives the multicast. The MLD protocol is used by IPv6 switches to discover the presence of multicast listeners (for example, nodes that want to receive multicast packets) on their directly attached links, and to discover specifically which multicast addresses are of interest to those neighboring nodes. It is used for discovering local group and source-specific group membership. The MLD protocol provides a means to automatically control and limit the flow of multicast traffic throughout your network with the use of special multicast queriers and hosts.
Multicast Queriers and Hosts A multicast querier is a network device, such as a switch, that sends query messages to discover which network devices are members of a given multicast group. A multicast host is a receiver, including switches, that send report messages to inform the querier of a host membership. Implementing IPv6 Multicast IPv6 Multicast Routing Implementation Implementing IPv6 Multicast 2