IP Address

Class A

The largest grouping of addresses is the class A group. Class A network addresses can be identified by a unique bit pattern in the 32bit address.

Representation : 0nnnnnnn 11111111 11111111 11111111

The first eight bits of a class A address indicate the network number. The remaining 24 bits can be modified by the administrative user of the network address to represent addresses found on their “local” devices. In the representation the “n's" indicate the location of the network number bits in the address. The “l's" represent the locally administered portion of the address. As you can see, the first bit of a class A network address is always a zero.

With the first bit of class A address always zero, the class A network numbers begin at 1 and end at 127. With a 24-bit locally administered address space, the total number of addresses in a class A network is 224 or 16,777,216. Each network administrator who receives a class A network can support 16 million hosts. But remember, there are only 127 possible class A addresses in the design, so only 127 large networks are possible.

Here is a list of class A network numbers:

• 10.0.0.0
• 44.0.0.0
• 101.0.0.0
• 127.0.0.0

Notice that these network numbers range between 1.0.0.0 and 127.0.0.0, the minimum and maximum numbers.

Range : 1.0.0.0 - 127.0.0.0
Total Networks : 127
Total Addresses : 16,777,216

Class B

The next grouping of addresses is the class B group. Class B network addresses can be identified by a unique bit pattern in the 32-bit address.

10nnnnnn nnnnnnnn 11111111 11111111

The first 16 bits of a class B address indicate the network number. The remaining 16 bits can be modified by the administrative user of the network address to represent addresses found on their “local” hosts. A class B address is identified by the 10 in the first two bits.

With the first two bits of class B address containing 10, the class B network numbers begin at 128 and end at 191. The second dotted decimal in a class B address is also part of the network number. A 16-bit locally administered address space allows each class B network to contain 216 or 65,536 addresses. The number of class B networks available for administration is 16,384.
Here is a list of class B network numbers:

• 137.55.0.0
• 129.33.0.0
• 190.254.0.0
• 150.0.0.0
• 168.30.0.0

Notice that these network numbers range between 128.0.0.0 and 191.255.0.0, the minimum and maximum numbers, respectively. And remember that the first two dotted decimal numbers are included in the network number since the network number in a class B address is 16 bits long.


Range : 128.0.0.0 - 191.255.0.0
Total Networks : 16,384
Total Addresses : 65,536

Class C

The next grouping of addresses is the class C group. Class C network addresses can be identified by a unique bit pattern in the 32bit address.

110nnnnn nnnnnnnn nnnnnnnn 11111111


The first 24 bits of a class C address indicate the network number. The remaining 8 bits can be modified by the administrative user of the network address to represent addresses found on their “local” hosts. A class C address is identified by the 110 in the first three bits.

With the first three bits of class C address containing 110, the class C network numbers begin at 192 and end at 223. The second and third dotted decimals in a class C address are also part of the network number. An 8-bit locally administered address space allows each class C network to contain 28 or 256 addresses. The number of class C networks available for administration is 2,097,152.

Here is a list of class C network numbers:

• 204.238.7.0
• 192.153.186.0
• 199.0.44.0
• 191.0.0.0
• 222.222.31.0

Notice that these network numbers range between 192.0.0.0 and 223.255.255.0, the minimum and maximum numbers, respectively. And remember that the first three dotted decimal numbers are included in the network number since the network number in a class C address is 24 bits long.

Range : 192.0.0.0 - 223.255.255.0
Total Networks : 2,097,152
Total Addresses : 256