What is subnetting? List advantages and disadvantages of the same.
2 Answers


  • Subnetting allows you to divide one physical network whether a class A, B, or C into several smaller logical subnetworks.
  • The main idea of subnetting is borrowing bits from the host IP address and using them to create one or more networks within the network.
  • Furthermore, It permits using two or more local area networks (LANs) technology in the same network such as Ethernet and Toking ring.

Advantages of using subnetting:

  • It is useful to control and to reduce the network traffic by limiting number of broadcasts.

  • It is allowed any organization to subnet its network without needed to have a new network IP through an internet service provider (ISP).

  • Subnetting was so helpful to solve the problem of lacking IP addresses on the Internet.

  • Allowing to use two or more LAN technologies together in the same network.

  • Subnets also helpful to minimize the size of the routing tables on the internet since additional network numbers will not being added to the table.

a. When you want to isolate segments for security reasons such as accounting and sales segment.

b. When you want to isolate bad segments such as domination hosts which use most of the LAN Bandwidth.

Disadvantage Advantages of using subnetting:

  • Subnetting decreases the total number of IP addresses in the network but may need buying additional hardware such as a router. So, it may cost lots of money.

  • It cannot correct the lack of efficiency because companies still assign address block regarding to classes.


In order to create IP subnets, host bits are changed to network bits. This is often called borrowing bits. It is also often referred to as taking host bits and giving them to the network. By borrowing host bits, more IP subnets are created, but each subnet can support fewer hosts. To change a host bit to a network bit, the subnet mask must be changed. Remember, a binary 0 in the subnet mask means that bit is part of the host portion of an IP address. A binary 1 in the subnet mask means that bit is part of the network portion of an IP address. So, to change a bit from a host bit to a network bit, the binary value of the bit must be changed from 0 to 1 in the subnet mask. When calculating subnets, the following process should be used. Each step of the process will describe in detail later in this paper. 1. Determine the assigned IP address space. 2. Determine the number of subnets required based on the design of the existing network, along with the structure of the organization. It is common to assign a subnet to each department within the organization. 3. Based on the class of the IP address space and the number of required subnets, determine how many host bits need to be borrowed. Also determine how many hosts each subnet can support. 4. Calculate the decimal value and prefix value of the new subnet mask. 5. Apply the subnet mask to the assigned IP address space to calculate the network address of the new possible subnets, the broadcast address for each possible subnet, and the range of usable IP addresses in each possible subnet. 6. Assign IP addresses to all devices, including router interfaces that are connected to that subnet.

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