Here’s my take on this.
Think of a large IP network as a big city. A subnet, or subnetwork, is like creating smaller, distinct neighborhoods within that city. It’s a way to logically divide one large network into multiple, smaller network segments.
The primary reasons for doing this are performance and security. By segmenting the network, you can reduce unnecessary traffic because data can stay within its relevant “neighborhood” instead of being broadcast to the entire “city.” This also lets you apply specific security rules or access policies to each subnet.
The subnet mask is simply the tool that tells devices which part of an IP address identifies the neighborhood (the network) and which part identifies the specific house (the device). It’s a foundational concept for managing networks efficiently.