Both the IP address and its associated subnet mask contain 32 bits. However, the 32-bit IP address can be
represented in other formats. The common formats include decimal (base 10) and hexadecimal (base 16)
notation. The generally accepted format for representing IP addresses and subnet masks the doted decimal
notation in which the 32-bit field is divided into four groups of eight bits, also called a byte, that are
translated to decimal value and separated by dots. Each group of eight bits is called an octet. Thus, an IP
Address expressed as 110000000010100100001010001100011101110 in binary format can be broken into
its four octets: 110000000.101001000.101000110.011101110. These octets are converted to decimal value
in Figure 3.3.
First
Octet |
Binary Code |
1 |
1 |
0 |
0 |
0 |
0 |
0 |
0 |
| Decimal Value |
128 |
64 |
32 |
16 |
8 |
4 |
2 |
1 |
Second
Octet |
Binary Code |
1 |
0 |
1 |
0 |
1 |
0 |
0 |
0 |
| Decimal Value |
128 |
64 |
32 |
16 |
8 |
4 |
2 |
1 |
Third
Octet |
Binary Code |
1 |
0 |
1 |
0 |
0 |
1 |
1 |
0 |
| Decimal Value |
128 |
64 |
32 |
16 |
8 |
4 |
2 |
1 |
Fourth
Octet |
Binary Code |
0 |
1 |
1 |
1 |
1 |
1 |
1 |
0 |
| Decimal Value |
128 |
64 |
32 |
16 |
8 |
4 |
2 |
1 |
FIGURE 3.3: Binary Code 1100 0000.1010
1000.0111 1011
| The decimal value of the first octet is: |
128+64+0+0+0+0+0+0 = |
192 |
| The decimal value of the second octet is: |
128+0+32+0+8+0+0+0 = |
168 |
| The decimal value of the third octet is: |
128+0+32+0+0+4+2+0 = |
166 |
| The decimal value of the fourth octet is: |
0+64+32+16+8+4+2+0 = |
126 |
| In dotted decimal format this IP Address would be
expressed as: 192.168.166.126 |