knowledge
Overview
Subnetting divides a network into smaller, manageable segments, improving efficiency, security, and routing. Using a subnet mask, subnetting defines network boundaries and limits the number of hosts per subnet — making it essential for network segmentation, IP address organization, and routing design.
Terminology
| Term | Definition |
|---|
| Subnet Mask | 32-bit value separating the network and host portions of an IP address (e.g., 255.255.255.0) |
| Network Address | Identifies the start of a subnet; not assignable to a host (e.g., 192.168.1.0) |
| Host Address | Identifies an individual device within the subnet (e.g., 192.168.1.100) |
| Default Gateway | Device that routes traffic outside the local subnet (e.g., 192.168.1.1) |
| RFC 1918 | Standard defining private IP address ranges not routable on the public internet |
| CIDR | Classless Inter-Domain Routing; shorthand notation for subnet masks (e.g., /24) |
Core Concepts
Subnet Mask
- 32-bit value written as four bytes (e.g.,
255.255.255.0)
- Defines which bits belong to the network portion and which to the host portion
- Devices on the same subnet share the same network portion
Subnet Components
| Component | Purpose | Example |
|---|
| Network Address | Identifies the subnet itself; not assignable to hosts | 192.168.1.0 |
| Host Addresses | Assignable to individual devices on the subnet | 192.168.1.1 – 192.168.1.253 |
| Default Gateway | Routes traffic destined for other networks | 192.168.1.254 or 192.168.1.1 |
| Broadcast Address | Sends data to all hosts on the subnet; not assignable | 192.168.1.255 |
RFC 1918 Private IP Ranges
Private addresses are not routable on the public internet — used within local networks only.
| Class | Range | CIDR |
|---|
| A | 10.0.0.0 – 10.255.255.255 | 10.0.0.0/8 |
| B | 172.16.0.0 – 172.31.255.255 | 172.16.0.0/12 |
| C | 192.168.0.0 – 192.168.255.255 | 192.168.0.0/16 |
Why Subnet?
- Efficiency — reduces unnecessary broadcast traffic
- Security — isolates network segments from each other
- Routing — enables more precise and efficient routing decisions
- Management — organizes devices into logical groups
References / Images
- RFC 1918: Private IP Addressing Standards
- Subnet mask diagrams and CIDR notation examples
