Install guide

IP Multicasting 3
Introduction
This chapter describes IP multicasting and support for multicasting on the
switch.
Most IP packets are sent to a single host—unicast transmission—or to all hosts
on a network or subnetwork – broadcast transmission. Multicasting is an
alternative where packets are sent to a group of hosts simultaneously on a
network or sub-network. Multicasting is also known as group transmission.
A multicast environment consists of senders (IP hosts), routers and switches
(intermediate forwarding devices) and receivers (IP hosts). A multicast group
has a class D IP address (the first number in the IP address – the top four bits –
are 1110). Any IP host can send packets to a multicast group, in the same way
that they send unicast packets to a particular IP host, by specifying its IP
address. A host need not belong to a multicast group in order to send to it.
Packets sent to a group address are only received by members of the group.
The switch uses the Internet Group Management Protocol (IGMP) to track
multicast group membership, and one or more of the following protocols to
route multicast traffic:
■ Protocol Independent Multicast Sparse Mode (PIM-SM)
■ Protocol Independent Multicast Dense Mode (PIM-DM)
PIM Sparse Mode, and PIM Dense Mode must be enabled with a special
feature licence. To obtain one, contact an Allied Telesis authorised distributor
or reseller.
The switch uses the Internet Group Management Protocol (IGMP) to track
multicast group membership. For simple networks, the switch can be
configured to use IGMP proxy for multicast switching between VLANs. For
networks with an Ethernet ring topology, the switch can use Multicast VLAN
Registration (MVR) to route between VLANs.
The multicast routing protocols described in this chapter are dynamic and
respond to changes in multicast group membership. Interfaces on the switch
can instead be configured statically to send and/or receive multicast packets.
Static multicasting is described in “Static Multicast Forwarding” in the Internet
Protocol (IP) chapter of your Software Reference.
References
Internet Draft Protocol Independent Multicast - Sparse Mode (PIM-SM): Protocol
Specification (Revised), Internet Engineering Task Force, PIM WG, 1 March 2002
(draft-ietf-pim-sm-v2-new-05).
Internet Draft Protocol Independent Multicast - Dense Mode (PIM-DM): Protocol
Specification (Revised), Internet Engineering Task Force, PIM WG, 15 February
2002 (draft-ietf-pim-dm-new-v2-01).
RFC 2236, Internet Group Management Protocol, version 2.
RFC 2715, Interoperability Rules for Multicast Routing Protocols.