Wednesday, February 4, 2009

Subnet and Classless Addressing

As the Internet grew,the original classful addressing scheme became a limitation.On one hand,the IP address space was being exhausted.On the other hand,because all networks had to choose one of the three possible sizes,that means many addresses were unused.Two new mechanisms were invented to overcome the limitations,known as subnet addressing and classless addressing.These two addressing schemes are so closely related that they can be considered to be a part of single abstraction.The generalization is straight forward that means instead of having three distinct address classes,allow the division between prefix and suffix to occur on an arbitrary bit boundary.Let understand this situation with the help of an example,Consider a network that contains 9 hosts.Only four bits of host suffix are needed to represent all possible host values.However,a class C address,which has the fewest address hosts possible,devote eight bits to the host suffix.Classless addressing solves the problem by allowing an ISP(Internet Service Provider) to assign a prefix that is 28 bits long that means network can have up to 14 hosts.

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