Class B Subnetting

What is Subnetting ?

Subnetting is the process of borrowing bits from host bits. In any network we can not use all IP address for hots address. We lose 2 address for every subnet.
one IP is reserved for network address and one IP reserved for broadcast address for all host in the network..

Example: Lets take a Class B IP address 172.50.10.0/17
There are 6 main things to consider subnetting.

1. CIDR Value/Subnet Mask
2. No of Subnets
3. No of Hosts per Subnet
4. Range
5. Network Address and Broadcast Address
6. Valid Range

Network Address of given IP is 172.50.0.0 because in class B, 2 octet are reserved for network and 2 octet reserved for host address.
1- CIDR =17 means subnet mask
11111111.11111111.10000000.00000000
255.          255.        128.         0

2-No of Subnets
No of subnets=2^no of subnetted bits
In our case subnetted bit is 1 so No of subnets are 2^1=2 sub network

3-No of Host per subnet
No of hosts per subnet=2^no of host bits ( No of zeros)
in our case 2^7 x 2^8=2^15
here 7 bits in 3rd octet and 8 bits in 4th octet

4-Range
We have 2 subnet so first subnet will start from 172.50.0.0 and end at 172.50.127.255 because( in 3rd octet 2^7 and 4th octet 2^8) there are 2^15 hosts in a subnet. so
1st range
172.50.0.0 to 172.50.127.255

2nd range
172.50.128.0 to 172.255.255

For 1st Range
Network address :172.50.0.0
Broadcast address: 172.50.127.255
valid IP: 172.50.0.1 to 172.50.127.254

For 2nd Range
Network address :172.50.128.0
Broadcast address: 172.50.255.255
valid IP: 172.50.128.1 to 172.50.255.254