Each bit in the octet can be either a 1 or a 0. If the value is 1, it is counted as its decimal value, and if it is 0, it is ignored. If all the bits are 0, the value of the octet is 0. If all the bits in the octet are 1, the value is 255, which is 128+64+32+16+8+4+2+1.
By using the set of 8 bits and manipulating the 1s and 0s, you can obtain any value between 0 and 255 for each octet.
Table 1 shows some examples of decimal-to-binary value conversions.
Decimal Value |
Binary Value |
Decimal Calculation |
---|---|---|
10 |
00001010 |
8+2=10 |
192 |
11000000 |
128+64=192 |
205 |
11001101 |
128+64+8+4+1=205 |
223 |
11011111 |
128+64+16+8+4+2+1=223 |
IP Address Classes
IP addresses are grouped into logical divisions called classes. In the IPv4 address space, there are five address classes (A through E), although only three (A, B, C) are used for assigning addresses to clients. Class D is reserved for multicast addressing, and Class E is reserved for future development.
Of the three classes available for address assignments, each uses a fixed-length subnet mask to define the separation between the network and the node address. A Class A address uses only the first octet to represent the network portion, a Class B address uses two octets, and a Class C address uses the first three octets. The upshot of this system is that Class A has a small number of network addresses, but each class A address has a very large number of possible host addresses. Class B has a larger number of networks, but each class B address has a smaller number of hosts. Class C has an even larger number of networks, but each Class C address has an even smaller number of hosts. The exact numbers are provided in Table 2.
Address Class |
Range |
Number of Networks |
Number of Hosts per Network |
Binary Value of First Octet |
---|---|---|---|---|
A |
1126 |
126 |
16,777,214 |
0xxxxxxx |
B |
128191 |
16384 |
65,534 |
10xxxxxx |
C |
192223 |
2,097,152 |
254 |
110xxxxx |
D |
224239 |
NA |
NA |
1110xxxx |
E |
240255 |
NA |
NA |
1111xxxx |