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group address), rather than one address. All the receivers join a group. Once they join the group, the
data sent to this group of addresses starts to be transported to the receivers. All the members in this
group can receive the data packets. This group is a multicast group.
A multicast group has the following characteristics:
z The membership of a group is dynamic. A host can join and leave a multicast group at any time.
z A multicast group can be either permanent or temporary.
z A multicast group whose addresses are assigned by IANA is a permanent multicast group. It is also
called reserved multicast group.
Note that:
z The IP addresses of a permanent multicast group keep unchanged, while the members of the
group can be changed.
z There can be any number of, or even zero, members in a permanent multicast group.
z Those IP multicast addresses not assigned to permanent multicast groups can be used by
temporary multicast groups.
Class D IP addresses range from 224.0.0.0 to 239.255.255.255. For details, see
Table 1-2.
Table 1-2 Range and description of Class D IP addresses
Class D address range Description
224.0.0.0 to 224.0.0.255
Reserved multicast addresses (IP addresses for permanent
multicast groups). The IP address 224.0.0.0 is reserved.
Other IP addresses can be used by routing protocols.
224.0.1.0 to 231.255.255.255
233.0.0.0 to 238.255.255.255
Available any-source multicast (ASM) multicast addresses
(IP addresses for temporary groups). They are valid for the
entire network.
232.0.0.0 to 232.255.255.255
Available source-specific multicast (SSM) multicast group
addresses.
239.0.0.0 to 239.255.255.255
Administratively scoped multicast addresses, which are for
specific local use only.
As specified by IANA, the IP addresses ranging from 224.0.0.0 to 224.0.0.255 are reserved for network
protocols on local networks. The following table lists commonly used reserved IP multicast addresses:
Table 1-3 Reserved IP multicast addresses
Class D address range Description
224.0.0.1 Address of all hosts
224.0.0.2 Address of all multicast routers
224.0.0.3 Unassigned
224.0.0.4
Distance Vector Multicast Routing Protocol (DVMRP)
routers
224.0.0.5 Open Shortest Path First (OSPF) routers
224.0.0.6 Open Shortest Path First designated routers (OSPF DR)
224.0.0.7 Shared tree routers
224.0.0.8 Shared tree hosts
224.0.0.9 RIP-2 routers
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