What Is Subnet Mask and CIDR Notation? A Beginner's Guide
When working with IPv4 networks, you will almost always see an IP address paired with a subnet mask or written in CIDR notation.
Understanding subnet masks is essential for network troubleshooting, router configuration, setting up local servers, and passing basic networking certifications.
/24) is a shorthand way of expressing how many bits belong to the network portion.
What is a subnet mask?
An IPv4 address consists of 32 bits divided into four octets. However, an IP address alone does not tell a device which part identifies the network and which part identifies the specific device on that network.
The subnet mask acts as a filter or template that tells the operating system and router where the network address ends and the host address begins.
Common home network subnet mask example
In most home Wi-Fi networks, you will see a subnet mask like this:
Subnet Mask: 255.255.255.0
The 255.255.255.0 mask indicates that:
- The first three numbers (
192.168.1) represent the network address. - The last number (
50) represents the specific host device on that network.
What is CIDR notation?
CIDR stands for Classless Inter-Domain Routing. Instead of writing out a full four-number subnet mask like 255.255.255.0, CIDR notation appends a slash and a number to the end of the IP address.
Example:
The /24 indicates that 24 bits (the first 3 octets of 8 bits each) are dedicated to the network, which corresponds exactly to 255.255.255.0.
Common Subnet Masks and CIDR Equivalent Table
| CIDR Notation | Subnet Mask | Usable IP Addresses | Typical Use Case |
|---|---|---|---|
| /32 | 255.255.255.255 | 1 | Single host route |
| /30 | 255.255.255.252 | 2 | Point-to-point router link |
| /24 | 255.255.255.0 | 254 | Standard home / office LAN |
| /16 | 255.255.0.0 | 65,534 | Large enterprise network |
| /8 | 255.0.0.0 | 16,777,214 | Very large network block |
Why is subnetting important?
- Organizes Traffic: Reduces network congestion by isolating local broadcast traffic within smaller subnets.
- Improves Security: Allows administrators to set up firewalls and access controls between different departments or subnets.
- Conserves IP Addresses: Helps ISPs and network admins assign precise address ranges without wasting unused addresses.
A subnet mask determines which part of an IP address belongs to the network and which part belongs to the individual device. Using CIDR notation like /24 makes subnet references much cleaner and easier to read!
Related IPScope guides
Learn how to find your local IP address and subnet details in How to Find Your Public vs Local IP Address on Any Device.
Check your external connection details using the IPScope Public IP Lookup.
