subnetting

subnet: A logical subdivision of an IP network

Why sub-netting is used?

Setting up logical divisions. Sub-netting helps you maintain clean separations within a network. For example, you can define boundaries between different departments in your organization, with one subnet for production, another for a marketing and for a finance.

Through sub-netting we can reduce wastage of IP addresses for a network

How to subnet a network?

subnet mask consists of 32 bits 

a subnet has 2 parts, one is network id and another one is the host id

Network ID: Any address bits which have the corresponding mask bit set to 1

Host ID/node ID: any address bits which have the corresponding mask bits set to 0

Host Id represents No.of devices in a network

for example: you have a class C address 192.168.1.0, the subnet mask for class c is 255.255.255.0 (11111111.11111111.11111111.00000000) 

Here 192.168.1 is a network position and 0 is a host position. That means 192.168.1.0 can have 255 devices in a network.

We can use CIDR notation to represent No.of 1's in a network.

ex: 192.168.1.0/24

1. sub-netting by No.of devices

      If you have 3 departments/sub networks, you have IP network 192.168.1.0 and each department should consist of 60 devices.

     So we use,   2^n-2>no.of devices

     Here 'n' represents No.of host bits in a subnet mask

     If we set 6 bits to Host ID

     :. 2^6-2=>64-2 

    That means we can set 62 devices per network.

    The subnet id is, 11111111.11111111.11111111.11000000 (255.255.255.192)

    Network 1: 192.168.1.0/26

    first host address 192.168.1.1 255.255.255.192

    last host address   192.168.1.62 255.255.255.192

    broadcast address 192.168.1.63 255.255.255.192

    Network 2: 192.168.1.64/26

    first host address 192.168.1.65 255.255.255.192

    last host address   192.168.1.126 255.255.255.192

    broadcast address 192.168.1.127 255.255.255.192

    Network 2: 192.168.1.128/26

    first host address 192.168.1.127 255.255.255.192

    last host address   192.168.1.190 255.255.255.192

    broadcast address 192.168.1.191 255.255.255.192

2.Sub-netting by No.of Networks

    If you have 3 departments/sub networks, you have IP network 192.168.1.0 

    So we use,  2^n>No.of networks

    here 'n' represents No.of Host bits that we should convert into network bits from left to right.

    If we convert 2 bits into network id, that means 4 sub-networks per a network.

    :. 2^2=4

    That means if we converts 2 host id bits as network bits, we can devided network into 4 sub-networks

    The subnet Id is, 11111111.11111111.11111111.11000000(255.255.255.192)

    Network1:192.168.1.0/64

    Network2:192.168.1.64/64

    Network3:192.168.1.128/64

    Network4:192.168.1.192/64