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Internet Addresses
Internet addressing uses a 32-bit address field. The
bits in this address field are numbered 0 to 31. The 32-bit address
field consists of two parts: a network number and a host number whose
boundaries are defined based on the class of IP address. Hosts attached
to the same network must share a common prefix designating their network
number.
Four types of IP classes lend themselves to different
network configurations, depending on the desired ratio of networks
to hosts. Figure 2 shows the format of IP address
classes.
Figure 2: IP Address Classes
- Class A—The leading bit is set to 0, a 7-bit number,
and a 24-bit local host address. Up to 125 class A networks can be
defined, with up to 16,777,214 hosts per network.
- Class B—The two highest-order bits are set to 1
and 0, a 14-bit network number, and a 16-bit local host address. Up
to 16,382 class B networks can be defined, with up to 65,534 hosts
per network.
- Class C—The three leading bits are set to 1, 1,
and 0, a 21-bit network number, and an 8-bit local host address. Up
to 2,097,152 class C networks can be defined, with up to 254 hosts
per network.
- Class D—The four highest-order bits are set to 1,
1, 1, and 0. Class D is used as a multicast address.
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