Subnetting And Supernetting

Sub netting

Take one IP address and break it down using CIDR notation to a group of several addresses

Sub net mask:To determine which portion of IP address is for the network and which portion is for node or host.

Class A : N.H.H.H
255.0.0.0

Class B: N.N.H.H
255.255.0.0

Class C:  N.N.N.H
255.255.255.0

N->Network    ,    H->Host

To determine sub nets:  2^bits borrowed

To determine valid hosts : 2^ (host bit)-2

SUB-NETTING  IP address 192.168.1.10 / 27

1-12.7 —> Class A

128-191 –>Class B

192-223–>Class C
255.255.255.0

From classification we can distinguish that the IP address belong to CLASS C

 192.168.1.10

192 belong to Class  C.
11111111 .  11111111.  11111111.00000000        

255.255.255. 0                                                                                                                         

as there are  3 network portions

255.255.255 .  0 0 0 0 0 0 0 0    (after cutting 3 bits from 8 bits 5  bits are left )               we cut  3 zero’s
8×3= 24
192.168.1.10 / 27
in order to reach 27 from 24 we borrow 3 bits(25,26,27)
2^n (n-->bits borrowed) 

2^3 = 8 sub nets  

(2^host bit)-2 

(2^5)-2 

32-2=30    means 30 PC’S per sub net    

        Super-netting

In super-netting multiple networks are combined into bigger networks termed as super net

This  process of forming a super net is  called super netting.

 

 Example:

Suppose we combine these 6 networks having IP addresses

1. 172.168.197.0/24
2.  172.168.198.0/24
3. 172.168.199.0/24
4. 172.168.200.0/24
5. 172.168.204.0/24
6. 172.168.206.0/24

    

Here we have add the no of bits which are same till 110 and we get our CIDR as 20
Now we will convert the bits into 0 which are not same after 1100
and we will get our Super net IP address as:
172.168.11000000.0/24
Now converting third octet into decimal we get the Super net IP address as:

172.168.192.0/20