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Catalyst 3750-X and 3560-X Switch Software Configuration Guide
OL-25303-03
Chapter 1 Implementing IPv6 Multicast
Information About Implementing IPv6 Multicast
Packets delivered to group members are identified by a single multicast group address. Multicast packets
are delivered to a group using best-effort reliability, just like IPv6 unicast packets.
The multicast environment consists of senders and receivers. Any host, regardless of whether it is a
member of a group, can send to a group. However, only members of a group can listen to and receive the
message.
A multicast address is chosen for the receivers in a multicast group. Senders use that address as the
destination address of a datagram to reach all members of the group.
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.
Note IPv6 Multicast Routing is supported only on the IP Services image.
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.
Multicast Listener Discovery Protocol for IPv6
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.
The difference between multicast queriers and hosts is as follows:
• A 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 host is a receiver, including switches, that send report messages to inform the querier of a host
membership.
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