Sunday, April 21, 2013

Logical Addressing & IP Addressing

Logical addressing is a function of the network layer of the OSI model. Unlike  hardware address( MAC ADDRESS) it provides a hierarchical structure to separate networks. A logical address identifies not only  a unique HOST ID , but also the network  that host belongs to . These are not hard-coded onto hosts and can be freely changed.

Two most common protocols used are IPX (INTERNETWORK PACKET EXCHANGE) and IP( INTERNET PROTOCOL).IPX was predominantly used on novell  networks,but is mostly deprecated. 

Nowadays IP is mostly used and their are already two versions of IP in the market.these are as follow
  1. IPv4 (32- bits)
  2. IPv6 (128-bits)
IP was developed by the department of Defence(DoD) during 1970' was included in a group of protocols that became to be known as TCP/IP suite.


IP addressing is just similar to the addressing of your home. Just as when we need a post from an outside city we require a Source address and a Destination address on the envelop , in the same way when packets are routed in Layer 3, they require address which are unique throughout the network.

NOTE- unlike MAC address ,  these are unique throughout the world and not just the network in which they are.

Each ip address has its subnet mask  which is decoded into bcd format which represent the actual ip address of network as well as the host
Things related to an IP address
  1. HOST ID
  Firstly , lets understand how does an IP address ( version 4) looks like

The above example is also called as decimal notation because of the periods used in representing it . here each block consist of 8 bits hence the range 0- 255 is available for each block. As a result  the total available permutations are  232 

But even this is getting over and hence we have to introduce ip version 6 which has more address space available and more security implementations.

Their are mainly 5 class through which we differentiate IPv4 address.These are as follow .

  1. Class A                               ( 0-126)
  2. Class B                               (128-191)
  3. Class C                               (192-223)
  4. Class D                               (224-239)
  5. Class E                               (240-254)

Note that range give beside them denotes the range of only 1st block of IPv4. IP address  has been reserved for  research purpose and is also called as the Loop back IP . This address has been used a lot by the crackers who try to avoid the auto updation of their pirated software suits whereas students sometime use it to play pranks on their mates.

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