if an ip address is given and it is divided into 4 subnets then what is the length of subnetwork ?

Question

what is the length of subnet ID. plz someone explain me with an example..plz..

Comments

Ip address belong to which class ?

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class C

Answer 1

I think ,

An ip address in class c has 24 bit reserved for network id and 8 bit for host id part .

Now since they say they need 4 subnets . so subnets bits are actually borowed from host id 

so 4 subnets , Log₂ (4) = 2 bits are taken from host id .

so now remaining size of host field is 8-2= 6 bits 

 length of subnet id is 26 bits ( 24 bits of host + 2 bit of subnet ) 

So now subnet size will be 2^6 

But no of Ip address that would be assigned here 2^6 - 2 .

Comments

right @manojk , bt why r we using this formula only..how does this formula came log2(1024)..??

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This is the basic representation of Decimal into binary....if we have n bits then 2^n different combinations can be made out of 0 and 1. so...think in reverse...if you have to have 2^n different combinations you will be needing n bits which is nothing but log₂ (2^n).

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ya..ok..thank u...:)

Answer 2

If we have to make 4 subnets then we have to choose 2 bits (00, 01,10,11) . As it is class C, 3 octets are for NID and 1 octet is for HID. Among Hosts we have to choose 2 bits so no of remaining hosts are configured  from last 6 bits i.e. 2^6 -2