Subnet Calculator – Calculation

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Understanding Subnets and IP Networks

What Is a Subnet?

A subnet (short for subnetwork) is a division of an IP network, which is a system of communication protocols used on the Internet and similar networks. The internet protocol suite, commonly known as TCP/IP (Transmission Control Protocol/Internet Protocol), governs how data is transmitted across these networks.

Subnetting is the process of dividing a network into smaller subnetworks, enabling better organization, security, and efficient use of IP addresses. Routers act as the physical boundary between different subnets, managing the exchange of data between them.

IP Addressing and Subnet Masks

An IP address consists of two main parts:

Network Number (Routing Prefix) – Identifies the network.
Host Identifier (Rest Field) – Uniquely identifies a device within the network.

Both IPv4 (the most commonly used addressing system) and IPv6 (a newer system growing in adoption since 2006) utilize Classless Inter-Domain Routing (CIDR) notation to represent network prefixes. CIDR helps define network and device identifiers uniquely.

For IPv4, networks are often defined using subnet masks, which distinguish the network portion from the host portion of an IP address. These subnet masks can be written in dot-decimal notation (e.g., 255.255.255.0). In IPv6, the network prefix serves a similar function, with the prefix length indicating the number of bits assigned to the network.

Subnetting Before and After CIDR

Before CIDR was introduced, IPv4 networks were classified into predefined categories (Class A, B, or C), each with a fixed range of IP addresses and a corresponding default subnet mask. However, this system was inefficient for managing IP address allocation.

With the introduction of CIDR, subnetting became more flexible, requiring both an IP address and a custom network mask when assigning addresses to network interfaces. This allowed for more efficient allocation of IP addresses, reducing waste and improving scalability across modern networks.