M denotes the multicast address bits.
R denotes the reserved bits.
The class of an IP address can be established from the first four bits of the first byte of the IP address. The
value of the first octet in the IP address resolves to the class within the range of which the IP address falls.
Table 2-1 summarizes the possible range of IP addresses for the different IP address classes that were
previously discussed.
Table 2-1. Range of IP Addresses per Class
Class Possible Range of Addresses
A 0.0.0.0 through 127.255.255.255
B 128.0.0.0 through 191.255.255.255
C 192.0.0.0 through 223.255.255.255
D 224.0.0.0 through 239.255.255.255
E 240.0.0.0 through 247.255.255.255
Table 2-2 shows the maximum number of networks and hosts that can be derived within each class.
Table 2-2. Networks and Hosts per Class
Class Max Number of Networks Max Number of Hosts per Network
A 126 (2^7??“2) 16777214 (2^24??“2)
B 16384 (2^14) 65534 (2^16??“2)
C 2097152 (2^21) 254 (2^8??“2)
D ??” ??”
E ??” ??”
Note
Class A??”The maximum number of networks is reduced by 2 to account for the reserved network IP
address of 0.xxx.xxx.xxx and 127.xxx.xxx.xxx.
The maximum number of hosts per network is also reduced by 2 to account for the reserved host IP
address in which all the host ID address bits are either 1 or 0??”that is, the network address and the
broadcast address.
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