Subnetting

• Subnetting is process of dividing the network into smaller networks. Each smaller network is referred as subnet (sub-network)
• private cidr ranges

10.0.0.0/8
172.16.0.0/12
192.168.0.0/16

• Let me create a private network of 500 devices approximately

2^n ~= 500
n = 9
N = 32 - 9 = 23
ip: 192.168.0.0/23

• In this network we need to create two subnetworks of size’s approximately 200

2^n ~= 200
n = 8
N = 24
network cidr: 192.168.0.0/23 => 192.168.0.0 to 192.168.1.255
network sm: 11111111.11111111.11111110.00000000
ip        : 192     .168     .00000000.0
sm1:        11111111.11111111.11111111.00000000
subnet1: 192.168.0.0/24
ip        : 192     .168     .00000001.0
sm2:        11111111.11111111.11111111.00000000
subnet2: 192.168.1.0/24

network: 11111111.11111111.11111110.00000000 /23
subnet:  11111111.11111111.11111111.00000000 /24
--------------------------------------------------
                   192.168.0000000x.0/24
                   192.168.00000000.0/24 => 192.168.0.0/24
                   192.168.00000001.0/24 => 192.168.1.0/24

• Lets create a network with approximately 8000 devices and create 4 subnets of approximately 2000 each

Network: 
2^n ~= 8000
n = 13
N = 32-13 = 19

cidr => 172.16.0.0/19
SM:     11111111.11111111.11100000.00000000

subnet:
2^n ~= 2000
n = 11
N = 32-11 = 21

NETWORK SM: 11111111.11111111.11100000.00000000
SUBNET  SM: 11111111.11111111.11111000.00000000
------------------------------------------------
                       172.16.000xx000.0/21

               Subnet1 172.16.00000000.0/21 => 172.16.0.0/21
               Subnet2 172.16.00001000.0/21 => 172.16.8.0/21
               Subnet3 172.16.00010000.0/21 => 172.16.16.0/21
               Subnet4 172.16.00011000.0/21 => 172.16.24.0/21

• Lets create a network of 1000 devices with 4 subnets of 250 devices each

Network:

2^n ~=  1000
n = 10
N = 32-10 = 22

cidr ip: 192.168.0.0/22
SM Network: 11111111.11111111.11111100.00000000

Subnet ~= 250
2^n ~= 250
n = 8
N = 24

SM Network: 11111111.11111111.11111100.00000000
SM Subnet:  11111111.11111111.11111111.00000000
------------------------------------------------
                      192.168.000000xx.0/24
                      192.168.00000000.0/24 => 192.168.0.0/24
                      192.168.00000001.0/24 => 192.168.1.0/24
                      192.168.00000010.0/24 => 192.168.2.0/24
                      192.168.00000011.0/24 => 192.168.3.0/24

• Lets create a network of 400000 (4 lakh devices) with 8 subnets of approximately 50000 devices.

Network:
2^n ~= 400000
n = 19
N = 32-19 = 13

cidr network: 10.0.0.0/13
SM Network: 11111111.11111000.00000000.00000000

subnet ~= 50000
2^n ~= 50000
n = 16
N = 32-16 = 16


SM Network: 11111111.11111000.00000000.00000000
SM Subnet:  11111111.11111111.00000000.00000000
------------------------------------------------
                  10.00000xxx.0.0/16
                  10.00000000.0.0/16 => 10.0.0.0/16
                  10.00000001.0.0/16 => 10.1.0.0/16
                  10.00000010.0.0/16 => 10.2.0.0/16
                  10.00000011.0.0/16 => 10.3.0.0/16
                  10.00000100.0.0/16 => 10.4.0.0/16
                  10.00000101.0.0/16 => 10.5.0.0/16
                  10.00000110.0.0/16 => 10.6.0.0/16
                  10.00000111.0.0/16 => 10.7.0.0/16

• Exercise: Lets create a network of 400000 (4 lakh devices) with 16 subnets of approximately 25000 devices.