Subnetting In ClaasFul IP Addressing
As we already know that, The classful subnetting is also called Fixed length subnetting. The Fixed length subnetting contain the following properties.
- Sizes of all sub networks are same.
- Subnets of all sub networks are same.
- All the sub networks have equal number of hosts.
Let understand with example
Example-01
Suppose
- We have a big single big network having IP Address 205.10.20.0.
- We want subnetting. So, divide this network into 2 subnets.
As given IP belongs to Class C So, 24 bits are used for net ID and 8 bits are used for Host ID.
For creating two subnets (sub networks) and to represent their subnet IDs, we require 1 borrowed-bit from Host part.
So,
- We borrowed one bit from the Host part.
- If borrowed bit = 0, then it will represent the first subnet.
- If borrowed bit = 1, then it will represent the second subnet.
Note: After borrowing one bit, Host ID part remains with only 7 bits.
IP Address of the two subnets are
- 10.20.00000000 = 205.10.20.0
- 10.20.10000000 = 205.10.20.128
For First Subnet
- IP Address of the subnet = 205.10.20.0
- Total number of IP Addresses = 27= 128
- Total number of hosts = 128 – 2 = 126
- Range of IP Addresses = [205.10.20. 00000000 to 205.10.20. 01111111] = [205.10.20.0 to 205.10.20.127]
- Direct Broadcast Address = 205.10.20.01111111 = 205.10.20.127
- Limited Broadcast Address = 255.255.255.255
For Second Subnet
- IP Address of the subnet = 205.10.20.128
- Total number of IP Addresses = 27= 128
- Total number of hosts = 128 – 2 = 126
- Range of IP Addresses = [205.10.20.10000000 to 205.10.20.11111111] = [205.10.20.128 to 205.10.20.255]
- Direct Broadcast Address = 205.10.20.11111111 = 200.1.2.255
- Limited Broadcast Address = 255.255.255.255
Important Note: Number of subnets depends upon the number of borrowed bits. We can define this relation through the following formula.
Number of subnets = 2n. where “n” is number of borrowed bits. So, if number of borrowed bits are 2 then subnets will be 22 = 4.
If given IP= 205.10.20.0. then first IP Address of each of four subnets are
- 10.20.00000000 = 200.1.2.0
- 10.20.01000000 = 200.1.2.64
- 10.20.10000000 = 200.1.2.128
- 10.20.11000000 = 200.1.2.192