Computer networks

Question

How we do supernetting??

Answer 1

The requirement of supernetting can be understood as follows :

When we are interested in using a particular class network , say class C network , but as we know no. of hosts that can be accomodated in a single class C network = 2⁸ - 2 = 254(since no. of host bits in class C = 8 bits and 1st address of every network is netid and last address is direct broadcast address of the network).

And suppose we need 1016 addresses but that of class C , then we need to combine the networks of class C. This is done by increasing the no. of hosts by taking some bits from netid.So suppose in this case, initially we had 8 bits for hosts , now we need to have 10 bits for hosts , so we take away 2 bits from netid.

It is nothing but supernetting of 4 class C networks in this case.Supernetting is just opposite of subnetting.In subnetting we divide a network into smaller subnetworks when we need to less addresses and hence in order to avoid wastage of address we do subnetting and when we have shortage of address in a single network we combine the networks which is known as supernetting.

Comments

Could u give the eg??

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Yes sure.

Consider a question , 

In class C , if supernet mask is 255.255.252.0 , then no. of networks that can be joined = ?

For this we have to know the default mask of the class C address which is 255.255.255.0 , so now we need to know how many bits are borrowed from this default mask to given supernet mask.We write the binary form of supernet mask which is :

11111111 11111111 11111100 00000000 

In this we can see the last 2 1's of 3rd octet are now converted to 0's.Hence 

no. of bits borrowed = 2

Hence no. of networks that can be joined = 2² = 4

Actually the last 2 0's in the 3rd octet in this case are supernet bits so they indicate what is the network.So no. of supernet bits = No. of 1's in the default mask which has turned into 0 due to supernet mask.

So if it is 01 instead of 00 , it means that it is the 2nd network of class C in the supernetwork which is formed.I hope now u have got the concept.

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@Habibkhan :- 4 Class c networks,when combined with supernet will give 1016 or 1024-2 ?