Network Devices

One problem with the classfull addressing is that each class is dividing into a fixed number of blocks with each block having the fixed size. Let’s look

Class A

Class A is divided into 128 blocks with each block having a different net id. First block covers address from 0.0.0.0 to 0.255.255.255 (net id 0). The second block covers address 1.0.0.0 to 1.255.255.255 (net id 1). The last block covers address form 127.0.0.0 to 127.255.255.255 (net id 127).

Note: each block of addresses the first byte (net id) is the same, but the other three bytes (host id) can take any value in the given range.

The first and last block in this are reserved for special purpose as we will discuss shortly. In addition one block is used for private address. The remaining 125 blocks can be assigned to organization. This means that the total number of organization that can have class A address is only 125. However, each block in this class contains 16,777,216 addresses. This address is called network address. It defines the network of the organization, not individual hosts. The organization is not allowed to use last address; it is reserved for a special purpose. Class A address is design for large organization with a large number of hosts or routers attached t their network.

Class B

Class B is divided into 16,384 blocks with each block having a different net id. Sixteen blocks are reserved for private addresses, leaving it 16,368 blocks for assignment to organization. The first block covers address form 128.0.0.0 to 128.0.255.255 (net id 128.0). the last block covers address from 191.255.0.0 to 191.255.255.255 (net id 191.255).

Note: each block of address the first 2 bytes net ID are same but other 2 bytes are host ID can take any value in the given range.

There are 16,368 blocks that can be assigned. This means that the total number of organization that can have class B address is 16,368. However, each block in this class contain 65,536 addresses, the organization should be large enough to use all of these addresses.

Class B was designed for mid size organization that many have tens of thousands of hosts or routers attached to their network. However, the number of addresses in each block 65,536 is larger than the needs of most midsize organizations.

Class C

Class C is divided into 2097152 blocks with each block having a net ID. 256 blocks are used for private addresses, leaving 2,096,896 blocks for assignment to organization. The first block covers address from 192.0.0.0 to 192.0.0.255 (net id 192.0.0). the last address covers address from 223.255.255.0 to 223.255.255.255 (net id 223.255.255).

Note: the each block of address the first 3 bytes are the same but last one byte can take any value in the given range. There are 2096902 blocks that can be assigned have a class C address is 2096902. However, each block in this class contains 256 addresses, which means the organization should be small enough to need less than 256 addresses.

Class C was designed for small size organization with a small number of hosts or routers attached to their network.

Class D

There just one block of class D addresses. It designed for multicasting. Each address in this class is used to define one group of hosts on the internet. When a group is assigned an address in this class, every host that is member of this group will have a multicast address in addition to its normal (unicast) address.

Class E

There is just one block also in class E address. It was designed for used as reserved address. The last address in this class 255.255.255.255 is used for a special address.

Network Addresses

Network addresses play a very important role in classfull addressing. A classful address has several properties:

We try to understand with the example:

Given the network address 132.210.0.0, class is B  because the first byte is between the 128 to 191. The block has net id of 132.21, the address range from 132.21.0.0 to 132.21.255.255.