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Networks attached to the Internet are assigned class types that determine the maximum
number of possible hosts per network. The previous figure illustrates how the net and host
portions of the IP address differ among the three classes. Class A is assigned to networks that
have more than 65,535 hosts; Class B is for networks that have 256 to 65534 hosts; Class C
is for networks with less than 256 hosts.
Class
A
B
C
Note: All network addresses outside of these ranges (Class D and E) are either reserved or set
aside for experimental networks or multicasting.
When an IP address's host portion contains only zero(s), the address identifies a network and
not a host. No physical device may be given such an address.
The network portion must start with a value from 1 to 126 or from 128 to 223. Any other
value(s) in the network portion may be from 0 to 255, except that in class B the network
addresses 128.0.0.0 and 191.255.0.0 are reserved, and in class C the network addresses
192.0.0.0 and 223.255.255.0 are reserved.
Appendix B - IP Concepts
IP Network Classes
Maximum
Network Addresses (Host
Number of
Portion in Parenthesis)
Networks in
Class
126
1(.0.0.0) to 126(.0.0.0)
16,382
128.1(.0.0) to 191.254(.0.0)
2,097,150
192.0.1(.0) to 223.255.254(.0)
DI-206 ISDN Remote Router
Maximum
Number of
Hosts per
Network
16,777,214
65,534
254
159
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