3com 4210 PWR 9-Port 3CR17341-91-ME ユーザーズマニュアル

IP addressing uses a 32-bit address to identify each host on a network. An 
example is 01010000100000001000000010000000 in binary. To make IP 
addresses in 32-bit form easier to read, they are written in dotted decimal 
notation, each being four octets in length, for example, 10.1.1.1 for the address 
just mentioned.

Each IP address breaks down into two parts:

■

Net ID: The first several bits of the IP address defining a network, also known as 
class bits.

■

Host ID: Identifies a host on a network.

For administration sake, IP addresses are divided into five classes, as shown in the 
following figure (in which the blue parts represent the address class).

Figure 34   IP address classes

Table 48 describes the address ranges of these five classes. Currently, the first 
three classes of IP addresses are used in quantity.

0

Net-id

Host-id

1

Net-id

Host-id

0

1

Net-id

Host-id

0

1

1

Multicast address

0

1

1

1

Reserved

1

1

1

Class A

0

7

15

23

31

Class B

Class C

Class D

Class E