When IP addresses first started out, they were arranged into classes. The class of the address is what helped determine what the size of the network was going to look like. This type of addressing is no longer in use, as net masks can now be used in what is known as classless addressing.

There are four octets that make up an IP address. (ex. 192.168.0.1) These octets are represented by an a, b, c, and d, in that order. The chart looks something like this:

Class     IP           Network ID   Host ID
A              a.b.c.d      a                       b.c.d
B              a.b.c.d      a.b                     c.d
C             a.b.c.d       a.b.c                  D

Let us take a look at each of the individual classes:

Class A addresses are given to various network with a large number individual hosts, allowing up to 126 networks. This s because it uses the first octet for the network ID. The first bit in the octet is always fixed to “0″, and the remaining bits are all set to a value of “1″, which is what makes up the network ID. The remaining octets are used for the different host’s IDs. Within the different allotted hosts per each network, there are allowed about 17 million hosts.

Class B is used for medium sized networks. It allows for up to 16,384 different networks because of the fact that it uses the first two octets for number allocation.The total number of hosts allowed for this class is 65,000. While this seems like quite a large number, it’s not when you compare it with Class A addresses.

The Class C addresses are used in small LANs, also known as local area networks. These can stretch from use around a large building to one that serves the inside of a small household. This class allows for 2 million networks within the LAN, becuase of the fact hat is uses the first 3 octets for storing the numbers. The first three bits are fixed to 1 1 0, in corresponding order.The following 8 bits are used to contain the host ID, which may consist of 254 hosts per network.

Class D and E addresses are used for, well, not what you would think. Instead of being used for allocating hosts, Class D addresses are used for multicasting, and Class E addresses are reserved for future purposes.

Because we are slowly using up all available IP addresses in IPv4, IPv6 will become the new standard and will provide for many, many more addresses to be used.

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