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Sunday, January 28, 2018

Classless addressing

Classless addressing

In 1996, the internet authorities announced a new architecture called classless addressing. 
In classless addressing, variable-length blocks are used that belong to no classes. 
Classless addressing can have a block of 1,2,4,8,16,32,64,128,256, addresses, and so on.    
The class privilege was removed from the distribution to compensate for the address depletion. 
In classless addressing, the whole address space is divided into variable length blocks. Theoretically, blocks of 20,21,22,23,...,232 address.

 Two-Level Addressing

In Classless addressing the block is divided into two parts, the prefix and suffix. The prefix plays the role of netid; and the suffix plays the role of the hostid. 

All the address in the block have the same prefix; however each address has a different suffix. 

In classfull addressing the length of the netid, n, depends on the class of the address; it can be only 8,16, or 24. In classless addressing, the length of the prefix, n, depends on the size of the block; it can be 0,1,2,3,4,...,32.

In classless addressing, the value of n is referred to as prefix length; the value 32-n is referred to as suffix length.

Slash Notaiton

In classless addressing, the prefix length to each address is added to the address seperated by a slash. The notation is informally referred to as slash notation.
The slash notation is formally referred to as classless interdomain routing or CIDR (pronounced cider) notation.

example :

Network Mask

The idea of network mask in classless addressing is the same as the one in classful
A network mask is a 32-bit number with the n leftmost bits all set to 0s and the rest of the bits all set to 1s.

 Block Allocation

The Internet Corporation for Assigned Names and Numbers (ICANN) is responsible for allocating IP address. 

ICANN assigns a large block of addresses to an ISP (Internet Service Provider). ISP provider allocate addresses to individual internet users.

One of the advantages of CIDR architecture is address aggregation. ICANN assigns a large block of addresses to an ISP. Each ISP in turn divides its assigned block into smaller subblocks and grants the subblocks to its customers; many blocks of addresses are aggregated in one block and granted to one ISP. 

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