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IPv4 Multicast Address
1. IPv4 Multicast IP Address:
As specified by IANA (Internet Assigned Numbers Authority), Class D IP addresses are used as
destination addresses of multicast packets. The multicast IP addresses range from
224.0.0.0–239.255.255.255. The following table displays the range and description of several
special multicast IP addresses.
Multicast IP address range Description
224.0.0.0–224.0.0.255 Reserved multicast addresses for routing protocols
and other network protocols
224.0.1.0–224.0.1.255 Addresses for video conferencing
239.0.0.0–239.255.255.255 Local management multicast addresses, which are
used in the local network only
Table 9-1 Range of the special multicast IP
2. IPv4 Multicast MAC Address:
When a unicast packet is transmitted in an Ethernet network, the destination MAC address is the
MAC address of the receiver. When a multicast packet is transmitted in an Ethernet network, the
destination is not a receiver but a group with uncertain number of members, so a multicast MAC
address, a logical MAC address, is needed to be used as the destination address.
As stipulated by IANA, the high-order 24 bits of a multicast MAC address begins with 01-00-5E
while the low-order 23 bits of a multicast MAC address are the low-order 23 bits of the multicast IP
address. The mapping relationship is described as Figure 9-2.
Figure 9-2 Mapping relationship between multicast IPv4 address and multicast MAC address
The high-order 4 bits of the IP multicast address are 1110, identifying the multicast group. Only 23
bits of the remaining low-order 28 bits are mapped to a multicast MAC address. In that way, 5 bits
of the IP multicast address is not utilized. As a result, 32 IP multicast addresses are mapped to the
same MAC addresses.
IPv6 Multicast Address
1. IPv6 Multicast Address
An IPv6 multicast address is an identifier for a group of interfaces, and has the following format:
0XFF at the start of the address identifies the address as being a multicast address.
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