Subnetting Guide for Beginners and Network Engineers
Subnetting is the process of dividing a larger IP network into smaller, more manageable networks called subnets. It helps organize address space, reduce broadcast domains, and make networks easier to design and operate.
Whether you are learning networking fundamentals or managing production environments, understanding subnetting is essential.
What Is a Subnet?
A subnet is a smaller network carved out of a larger IP range. For example, instead of using one large network for every device, you can split that space into separate subnets for servers, users, printers, or branch sites.
This improves organization, scalability, and control.
What Is a Subnet Mask?
A subnet mask defines which part of an IP address represents the network and which part represents the host. For example, the subnet mask 255.255.255.0 corresponds to /24.
In a /24 network, the first 24 bits identify the network and the remaining 8 bits identify hosts.
What Does CIDR Mean?
CIDR stands for Classless Inter-Domain Routing. It is the slash notation used to describe network size, such as:
- /24 = 256 total addresses
- /25 = 128 total addresses
- /26 = 64 total addresses
- /27 = 32 total addresses
- /28 = 16 total addresses
As the slash number gets larger, the subnet becomes smaller.
How Many Usable IP Addresses Are in a Subnet?
In traditional IPv4 subnetting, two addresses are reserved in each subnet:
- Network address — identifies the subnet itself
- Broadcast address — used to reach all hosts in the subnet
That means the number of usable host addresses is usually:
Total addresses - 2
For example, a /24 has 256 total addresses, so it normally provides 254 usable IP addresses.
Example: 192.168.1.0/24
Let’s look at a common example:
- Network: 192.168.1.0/24
- Subnet mask: 255.255.255.0
- Network address: 192.168.1.0
- Usable host range: 192.168.1.1 to 192.168.1.254
- Broadcast address: 192.168.1.255
Common IPv4 Subnet Sizes
- /30 — 4 total addresses, 2 usable
- /29 — 8 total addresses, 6 usable
- /28 — 16 total addresses, 14 usable
- /27 — 32 total addresses, 30 usable
- /26 — 64 total addresses, 62 usable
- /25 — 128 total addresses, 126 usable
- /24 — 256 total addresses, 254 usable
Why Subnetting Matters
Good subnet design helps you:
- Use IP space efficiently
- Separate departments, sites, or services
- Improve routing design
- Reduce operational confusion
- Scale your network more cleanly
Subnetting in Real-World Environments
In production networks, subnetting is not just a classroom exercise. Teams often need to manage many networks across offices, customers, environments, or routing domains.
That is why an IPAM platform becomes valuable. Instead of relying on spreadsheets, teams can track subnets, IP allocations, and changes from one central place.
How IPAM365 Helps with Subnet Management
IPAM365 helps teams organize subnets, track IP usage, manage segmented environments, and maintain visibility as networks grow. It also supports multi-tenant environments and VRF-aware IP management for more advanced designs.
Also read: What is IPAM? and What is VRF?