Computer Networking

Transport Layer

Subnetting and Its Types

  • Subnetting is a process in which a single network is dividing into multiple sub-networks.
  • The sub-networks also called as subnets.


Following figure shows the sub networks of a large single network into 4 smaller sub networks

Subnet ID

  • Each sub network has its unique network ID known as its Subnet ID.
  • The subnet ID is created by borrowing some bits from the part of Host ID.
  • The number of bits borrowed from hosts depends on the number of subnets created.

Types of Subnetting

Subnetting of a network can be achieved through the following methods

1. Fixed Length Subnetting

Fixed length subnetting also called as classful subnetting. Fixed length subnetting hold 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.

2. Variable Length Subnetting

Variable length subnetting also called as classless subnetting. Variable length subnetting hold the following properties.

  • Sizes of all sub networks are not same.
  • Subnets of all sub networks are not same.
  • All the sub networks do not have the equal number of hosts.

Advantages of Subnetting

Subnetting improves the security because the administration and maintenance of sub networks is easy.

In simple words, management and maintenance of entire university is tough as compare to its different departments.

Disadvantages of Subnetting


Subnetting leads towards the loss of IP Addresses.

Two IP Addresses are always wasted for evry sub-network (subnet).In subnetting, One IP Address is wasted for its network address and other for its direct broadcasting address.


Subnetting leads toward more complicated communication process as compare to without subnetting communication.

After subnetting, the communication is done through the following 4 steps

  • First Identifying the network
  • Second Identifying the sub network
  • Third Identifying the host
  • And in the last, Identifying the process
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