The ?¬?rst 4 bits of a Class D address must be 1110. Therefore, the ?¬?rst octet
range for Class D addresses is 11100000 to 11101111, or 224 to 239. An IP address
that starts with a value in the range of 224 to 239 in the ?¬?rst octet is a Class D address.
As illustrated in Figure 1-30, Class D addresses (multicast addresses) include the
following range of network numbers: 224.0.0.0 to 239.255.255.255.
?– Class E: Although a Class E address category has been de?¬?ned, the Internet
Engineering Task Force (IETF) reserves the addresses in this class for its own research.
Therefore, no Class E addresses have been released for use in the Internet. The ?¬?rst 4
bits of a Class E address are always set to 1111. Therefore, the ?¬?rst octet range for
Class E addresses is 11110000 to 11111111, or 240 to 255.
Figure 1-30 Multicast Addresses
Within each class, the IP address is divided into a network address (or network identi?¬?er,
network ID) and the host address (or host identi?¬?er, host ID). The number of networks and
hosts vary by class. A bit or bit sequence at the start of each address, known as the high
order bits, determines the class of the address, as shown in Figure 1-31.
Figure 1-31 Address Classi?¬?cation
Figure 1-31 shows how the bits in the ?¬?rst octet identify the address class.
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