Classless Addressing Problems | Computer Networks

Classless Addressing

->To Reduce the Wastage of IP Addresses and give most Organisations Access to Internet,Classless addressing was Designed and implemented.

The Internet Authorities impose three main restrictions on this classless addressing,Those are Listed Below..

1.A block of Address Must be contiguos,Similarly like an array [contiguos-Next or together in sequence]

2.The number of Addresses should be in power of 2.

3.First address in a Block Should be Evenly Divisible by number of addresses in a block.

Mask

Mask Is used to define the block of addresses,In Classless Adressing Mask Ranges in between 0 to 32.

For Example:- If 205.17.37.38/28 is the block of Address in which 205.17.37.38 defines one of the addresses and /28 defines the mask.and the block of addresses will be separated by periods i.e dots(.).

CIDR(Classless Inter Domain Routing)

CIDR is nothing but the block of addresses and masks.[i.e used to find first and last address].

Let us Know few CIDR's in the below image but this is not neccessary

So Let us find the first and last address of given block of addresses with masks

Example:- 205.17.37.38(block of address)
28 is mask

As we all know that mask ranges from 0-32
Subtract that given mask with 32

So now if we subtract (32-28) we get 4.

First Convert Those given block of addresses into binary format

so we get 205.17.37.38 as(transformed into binary) 11001101 00010001 00100101 00100110(note that these are not separated by periods i.e is dots

Set Right foremost bits to zeros i.e as we got 4 from subracting masks i.e(32-28) [we must set right foremost bits i.e last 4 bits will be tranformed to zeros]

So now we get the first address as 11001101 00010001 00100101 00100000[last 4 bits changed to zero]
so the converting them into decimal we get 205.17.37.32[and this is our first address]

So now to find last address we need to set those right foremost four bits to one'si.e we get those block of address as 11001101 00010001 00100101 00101111 in which if it is converted into binary we get 205.17.37.47[this is the last address

So inorder to find for how many systems we can generate ipaddresses is subtract first address and last address.
in the above example we got first and last addresses as 32 and 47 so(32-47) we get 16.

so finally we can know that for 16 systems we can generate ip addresses

If you wanna try another example try it for Below question

205.16.39.37/27

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