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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. 

 

 

 

 

 

 

126

 

1(.0.0.0) to 126(.0.0.0)

 

16,777,214

 

 

16,382

 

128.1(.0.0) to 191.254(.0.0)

 

65,534

 

2,097,150

 

192.0.1(.0) to 223.255.254(.0)

 

254

 

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. 
 
The value(s) in the host portion of a physical device's IP address can be in the range of 0 
through 255 as long as this portion is not all-0 or all-255. Values outside the range of 0 to 
255 can never appear in an IP address (0 to 255 is the full range of integer values that can 
be expressed with eight bits). 
 
The network portion must be the same for all the IP devices on a discrete physical 
network (a single Ethernet LAN, for example, or a WAN link). The host portion must be