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Supernetting or Classless Inter Domain Routing in Computer Networks

Supernetting  or Classless Inter Domain Routing.

Supernetting is the process of aggregating or combing two or more networks. IPv4 support various classes namely CLASS A, CLASS B, CLASS C and CLASS D.
 
We can only combine classes of same type . That means we can combine two or more CLASS C network together. But we cannot combine a CLASS B network and a CLASS C network together to form a single network. 
 
For example we can combine two class  C  Networks.But it is not possible to combine a class B network and a class C network.Supernetting is also known as CIDR (classless inter domain routing).
 
  • Supernetting
  • Classless Inter Domain Routing
  • Combine multiple Network id's to a single network
  • To reduce the wastage of IP Address
 
Supernetting is just opposite to subnetting. That means in Subnetting  bits are borrowed from the host part to form the subnet id. But in Supernetting bits are borrowed from network part and the borrowed bits are made part of the host part.

Supernetting Procedure steps

1. Identify / List  the Networks to combine.

2. Ensure that all networks are of the SAME CLASS.

3. Convert all  IP addresses to corresponding binary format.

4. Find the common prefix from them in the binary format. Common prefix means the set of matching bit sequence from left to right.

5. Set the remaining bits to zero.

 

The number of bits in the common prefix will be less than the umber of bits in the network part of the given IPs.

 

Example:

192.168.98.0     11000000 10101000 01100010 00000000

192.168.100.0   11000000 10101000 01100100 00000000

192.168.105.0   11000000 10101000 01101010 00000000

--------------------------------------------------------------------------------------------

The part represented in red colour represet the common prefix. that means this part is same for all . 

Summarized route or Common Address= 11000000 10101000 01100000 00000000 

                                                         = 192.168.96.0 / 20

Length of the common prefix = Length of Network part = Netmask = 20

Thus subnet mask contains 20 ones followed by 12 zeros. = 11111111 11111111 11110000 00000000

                                                                                            = 255.255.240.0

 

 Real Time Situations when  Supernetting is Useful

1. An organization need to connect 300 computers in a network

Consider the following requirement. An organization need to connect 300 computers in a network.
 
A class C network can accommodate maximum of 28 - 2 = 254 hosts.
 
So we have to select a Class B network to full fill this requirement and can accommodate a maximum of 216 - 2 = 65534 hosts.
 
But if we use a class B network for this there is a wastage of  65534 - 300 = 65234 IP addresses.
 
Here comes the importance of supernetting. We can combine two class C networks and it can accommodate all 300 hosts.The  maximum  hosts possible on this network is 2 *  254 = 508 hosts. Here the wastage of IP addresses is considerably reduced.Here the wastage is only 308 IP addresses.
 
2. An organization need to connect 1000 computers in a network
 
A class C network can accommodate maximum of 28 - 2 = 254 hosts.
 
So we have to select a Class B network to full fill this requirement and can accommodate a maximum of 216 - 2 = 65534 hosts.
 
But if we use a class B network for this there is a wastage of  65534 - 1000 = 64534 IP addresses. 
 
We can combine Four class C networks and it can accommodate all 1000 hosts. The  maximum  hosts possible on this network is 4 *  254 = 1016 hosts. Here the wastage of IP addresses is considerably reduced.Here the wastage is only 16 IP addresses.
 

 Supernetting Advantages

Thus by combing class C Address space we can prevent the wastage or exhaustation of reserved Class B Address space. Hence the conservation of  reserved IP Address space is one of the biggest advantage of supernetting.  Also it helps to reduce the number of entries in the routing table.

Protocol in computer Network

 What is the significance of Protocol in a computer Network?

Protocol is the set of rules and regulations used for communication between devices on a network. A Protocols may be  hardware, software, or a combination of both.A protocol has Syntax, Semantics and Timing.

  • Syntax
  • Semantics
  • Timing
  • Syntax indicate What is to Communicate
  • Semantics indicate  How to Communicate
  • Timing indicate When to Communicate

If a protocol can provide accurate answer to the above three questions, then it is an accurate protocol.

Example: HTTP , FTP, TCP ,UDP , IP , ARP, RARP etc

Inefficiencies of IP addressing System

Inefficiencies of IP addressing System

The existing IPv4 IP addressing system is not flexible and not secure. It causes wastage of  so many addresses.
  • IPv4 is Not Flexible and Secure
  • Wastage of IP addresses
 
So it requires so many extensions to overcome these shortcomings.They are
  • Subnetting
  • Supernetting or CIDR(Classless Inter domain Routing)
  • Public and Private Host

Public IP Address and Private IP Address in Computer Networks

Public IP Address and Private IP Address

Public Host

Any computer accessing a public network like internet must have a  unique ip address.Such a host is termed as public host. IP address of the public host is termed as public IP address.

 
Private Host

The total IP addresses available  are very limited. So it is not possible to assign unique ip address to all computers in the world. Here comes the importance of private IP address. The following ranges of IP addresses are reserved for private IP.

  • 10.0.0.0         to   10.255.255.255
  • 172.16.0.0     to   172.31.255.255
  • 192.168.0.0   to   192.168.255.255

Inside a LAN or a private network computers can use these ip addresses. Two different private network may use the same set of private IP addresses.


These private hosts can access internet or a public network through a public host.That is the private host's identity will not be visible in the public network, but it shows only the IP address of the public host through which it is connected to the internet. That is Private host shows the IP address of the public host in the Internet environment,but in the local network it shows the private IP address.
 
A private network is typically a network that uses private IP address space.Private IP addresses were originally created due to the shortage of publicly registered IP addresses created by the IPv4 standard.
 
Merging two Private Networks
 
Internal networks  of two different organizations may use the same private IP addresses.Problem occurs when trying to merge two such networks. We may apply the following solutions.
  • One network must renumber
  • A NAT router must be placed between the networks.
 

How to find the Subnet Address in Computer Networks

How to find the Subnet Address ?

 

AND (logical AND Operation) the subnet mask with any valid host IP address on the network will yield the subnet address.

Example

Given the subnet mask and any valid host IP address,

Subnet mask is        255.255.255.240
Host IP address       200.129.  41.23

Find the corresponding subnet address?

Subnet mask is        255.255.255.240 = 255.255.255.1111 0000

Host IP address       200.129.  41.23    = 200.129.  41.0001 0111


Last octet to binary:        200.129.  41.0001 0111
AND
subnet mask:          255.255.255.1111 0000

                                  200.129.  41.0001 0000

Subnet Address:                 200.129.  41.16