IP Multicast Overview 111
A multicast group can be either permanent or temporary. Part of addresses in the
multicast group are reserved by the IANA and are known as the permanent
multicast group. IP addresses of a permanent group are unchanged, but the
members in the group can change. The number of members in a permanent
multicast group can be random or even 0. Those IP multicast addresses that are
not reserved for permanent multicast groups can be used by temporary groups.
Ranges and meanings of Class D addresses are shown in Tabl e 114.
Reserved multicast addresses that are commonly used are shown Tabl e 115:
Ethernet Multicast MAC Addresses
When unicast IP packets are transmitted in Ethernet, the destination MAC address
is the MAC address of the receiver. However, when multicast packets are
transmitted, the destination is no longer a specific receiver but a group with
unspecific members. Therefore, the multicast MAC address should be used.
Multicast MAC addresses correspond to multicast IP addresses. IANA (Internet
Tabl e 114 Ranges and Meanings of Class D Addresses
Class D address range Meaning
224.0.0.0∼224.0.0.255 Reserved multicast addresses (addresses of
permanent groups). Address 224.0.0.0 is
reserved. The other addresses can be used by
routing protocols.
224.0.1.0∼238.255.255.255 Multicast addresses available for users
(addresses of temporary groups). They are
valid in the entire network.
239.0.0.0∼239.255.255.255 Multicast addresses for local management.
They are valid only in the specified local range.
Tabl e 115 Reserved Multicast Address List
Class D address Meaning
224.0.0.0 Base Address (Reserved)
224.0.0.1 Addresses of all hosts
224.0.0.2 Addresses of all multicast routers
224.0.0.3 Unassigned
224.0.0.4 DVMRP routers
224.0.0.7 ST routers
224.0.0.8 ST hosts
224.0.0.9 RIP-2 routers
224.0.0.10 IGRP routers
224.0.0.11 Mobile agents
224.0.0.12 DHCP server/Relay agent
224.0.0.13 All PIM routers
224.0.0.14 RSVP encapsulation
224.0.0.15 All CBT routers
224.0.0.16 Designated SBM
224.0.0.17 All SBMS
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