IP addresses are divided into classes based on their first octet. The three main classes are A, B, and C. Each class has a different range of possible values for the first octet and is used for different types of networks.

IP Classes:

  1. Class A:
    • First Octet Range: 1-126
    • Example:
    • Default Subnet Mask:
    • Reserved for very large networks
  2. Class B:
    • First Octet Range: 128-191
    • Example:
    • Default Subnet Mask:
    • Suitable for medium-sized networks
  3. Class C:
    • First Octet Range: 192-223
    • Example:
    • Default Subnet Mask:
    • Used for small networks

Public and Private IP Addresses:

  • Public IP Address: These are routable on the Internet. They are unique and can be used to identify a device on the global network.
  • Private IP Address: These are reserved for use within private networks and are not routable on the Internet. They are used for internal communication within a network.

Commonly used private IP address ranges:

  • Class A: to
  • Class B: to
  • Class C: to

Calculating IP Range:

When calculating the IP range for a subnet, you need to consider the network address, the usable IP addresses, and the broadcast address. Here’s a basic formula:

  1. Network Address: This is the base address of the subnet, obtained by setting all host bits to zero.
  2. Usable IP Addresses: All addresses between the network address and the broadcast address, excluding both.
  3. Broadcast Address: This is the last address in the subnet, obtained by setting all host bits to one.


  • IP Address:
  • Subnet Mask:
  1. Network Address:
  2. Usable IP Range: to
  3. Broadcast Address:

Remember, these calculations may vary if you are using subnetting. Subnetting involves dividing a larger network into smaller sub-networks, allowing for better organization and utilization of IP addresses.

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