The IANA controls the assignment of IP multicast addresses. IANA has
assigned the IPv4 Class D address space to be used for IP multicast. Therefore,
all IP multicast group addresses fall in the range from 224.0.0.0 through
239.255.255.255. The Class D address is used for the destination IP address of
multicast traffic for a specific group. The source address of a multicast
datagram is the unicast address of the device sourcing the multicast flow to
the destination multicast address.
Reserved Link-Local
Addresses
The IANA has reserved addresses in the range 224.0.0.0 to
224.0.0.255 to be used by network protocols on a local network segment. A
router should never forward packets with these addresses. Packets with
link-local destination addresses are typically sent with a Time to Live (TTL)
value of 1 and are not forwarded by a router. Network protocols use these
addresses for automatic router discovery and to communicate important routing
information. For example, Open Shortest Path First (OSPF) Protocol uses the IP
addresses 224.0.0.5 and 224.0.0.6 to exchange link-state information.
Address 224.0.0.1 identifies the all-hosts group. Every multicast-capable
host must join this group. If a ping command is issued
using this address, all multicast-capable hosts on the network must answer the
ping request.
Address 224.0.0.2 identifies the all-routers group.
Multicast routers must join that group on all multicast-capable interfaces.
Globally Scoped Addresses
Multicast addresses in the range from
224.0.1.0 through 238.255.255.255 are called "globally scoped
addresses." They can be used to multicast data between organizations and
across the Internet. Some of these addresses have been registered with IANA,
for example IP address 224.0.1.1 has been reserved for Network Time Protocol
(NTP).
Source Specific Multicast Addresses
Addresses in the
232.0.0.0 to 232.255.255.255 range are reserved for Source Specific Multicast
(SSM). SSM is an extension of Protocol Independent Multicast (PIM), which
allows for an efficient data delivery mechanism in one-to-many
communications.
GLOP Addresses
Multicast GLOP (a word, not an
acronym) addresses in the range 233.0.0.0 to 233.255.255.255 can be used
statically by organizations that have an Autonomous System (AS) number
registered by a network registry and listed in the RWhois database. The second
and third octets of the domain multicast address are represented by the AS
number. For example, AS 62010 is written in hexadecimal format as
"F23A." This value is separated into two parts, F2 and 3A and those
numbers, converted to decimal would be 242 and 58. This would yield a multicast
GLOP address of 233.242.58.0/24. Multicast group addresses in that address
space can be used by the organization with AS 62010 and routed throughout the
Internet Multicast Backbone.
Limited Scope Addresses
Like
private IP address space that is used within the boundaries of a single
organization, "limited" or "administratively scoped"
addresses in the range 239.0.0.0 to 239.255.255.255 are constrained to a local
group or organization. Companies, universities, or other organizations can use
limited scope addresses to have local multicast applications that will not be
forwarded over the Internet. Typically, routers are configured with filters to
prevent multicast traffic in this address range from flowing outside of an AS.
Within an autonomous system or domain, the limited scope address range can be
further subdivided so that local multicast boundaries can be defined. This
subdivision is called "address scoping" and allows for address reuse
between smaller domains. These addresses are described in RFC 2365,
Administratively Scoped IP Multicast.