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What is the purpose of a subnet mask?

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A subnet mask is a 32-bit number that is used in computer networking to divide an IP address into network and host portions. Its primary purpose is to identify the network and host parts of an IP address so that routers can efficiently route packets across a network.

Let's break down the technical details:

  1. IP Address Format:
    • An IP address is a 32-bit numerical label assigned to each device connected to a computer network.
    • Example: 192.168.1.1
  2. Binary Representation:
    • Each octet of the IP address can be represented in binary (0s and 1s).
    • Example: 192.168.1.1 in binary might be 11000000.10101000.00000001.00000001.
  3. Subnetting:
    • Subnetting is the process of dividing an IP network into sub-networks or subnets. It helps in efficient utilization of IP addresses and enables the creation of smaller, more manageable networks.
  4. Network and Host Portions:
    • In an IP address, the network and host portions are divided by a subnet mask.
    • The subnet mask is also a 32-bit binary number, where the network bits are represented by '1's and the host bits by '0's.
    • Example: 255.255.255.0 in decimal is 11111111.11111111.11111111.00000000 in binary.
  5. Logical AND Operation:
    • The subnet mask is applied to the IP address using a bitwise AND operation.
    • The result of this operation determines the network to which the device belongs.
    • Example:
      • IP Address: 192.168.1.1 (11000000.10101000.00000001.00000001)
      • Subnet Mask: 255.255.255.0 (11111111.11111111.11111111.00000000)
      • Result: Network 192.168.1.0
  6. Routing:
    • Routers use the subnet information to determine how to forward packets. They look at the destination IP address and the subnet mask to decide the appropriate path.
  7. Address Allocation:
    • Subnetting allows for efficient allocation of IP addresses within an organization. Different subnets can be assigned to different departments or functions.