150Appendix E: Understanding IP and IP addressing

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

 

 

32 bits

 

147

234

11

101

1001 0011

1110 1010

0000 1011

0110 0101

Network number

 

Host number

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 373such 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).

 

 

 

297-8991-910 Standard 03.01 August 1999

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Cabletron Systems DMS-100 manual IP address structure, Class Range Description