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150 Appendix E: Understanding IP and IP addressing
297-8991-910 Standard 03.01 August 1999
not recommended. If connection to public networks is needed later, all the
addressing work must be repeated.
IP addresses
IP uses a 32-bit address, which consists of four sets of eight-bit numbers,
normally expressed in decimal notation. For example, 147.234.011.101 is a
valid IP address format.
IP addresses can be divided into a network number and a host number, as
shown in figure 28.
Figure 28 IP address structure
The addresses are assigned in one of three unicast classes—A, B, or C—
depending on the number of host addresses the institution can reasonably
expect to use. These ranges are identified by the first eight bits of the address
and are made up of the first one-to-three octets of the address. Each range
reserves less of the whole address for host numbers than the previous range.
Table 36 describes the ranges and uses of class A, B, and C addresses.
Table 36 IP address classes
Class Range Description
A 1 to 126 This is used for networks that can have a very large
number of nodes (hosts)—up to 16 581 373—such as
government agencies and major university systems
(for example, 111.0.0.0).
B 128 to 191 This is used for networks that can have up to 65 023
nodes, such as large corporations (for example,
129.191.0.0).
147 234 11 101
Network number Host number
1110 1010
0000 1011 0110 01011001 0011
32 bits