CCNA

Subnetting Vocabulary Decoded: Understanding the Language of IP Addressing

Jay Whale

09 Feb 2026 • 4 min read

Hey CCNA learners! 👋

One of our community members asked a great question about subnetting terminology, you know, those words we throw around that can feel confusing at first. Let's break down what each term actually means and how they relate to each other.

The Essential Terms

Mask / Subnet Mask

Think of a subnet mask as a filter that separates the "network portion" from the "host portion" of an IP address. It's literally a mask that covers part of your IP address.

Example: 255.255.255.0

The 255s say "this part identifies the network"
The 0 says "this part identifies individual hosts"

When you see an IP like 192.168.1.50 with mask 255.255.255.0, the mask tells you that 192.168.1 is the network, and .50 is a specific device on that network.

When I teach this topic, I always prefer to start with just referenceing N for Network, and H for host. So a mask is just a definition of which part of the numbers are the name of the network, and which parts of the for the hosts. Think of this another way, if I have a building with 1,000 rooms in it, and each room has 12 people. If I want to find John I need to start with the room he is in, and then look for the individual. IP addresses are no different, let's find the room (network) then lets find the person. But when have numbers like 192.168.1.50 I'm not sure which part of those numbers is the room number and which one is John. The subnetmask (mask) tell me that. So if the first 3 octects are the name of the network (192.168.1) and the last octect is the person (John - .50) then it's a lot easier for me to find John in room 192.168.1. The subnetmask would be N.N.N.H, the first 3 octects are the Network (N) and last one is the Host (H). However since we are using binary, we have to use 1's and 0's instead of N and H. So the subnet mask is 255.255.255.0.

CIDR (Classless Inter-Domain Routing)

This is just shorthand notation for subnet masks using a slash and a number.

Instead of writing 255.255.255.0, we write /24

Why 24? Because there are 24 ones in the binary version of that mask:
11111111.11111111.11111111.00000000 = 24 ones

Common conversions you'll see constantly:

/24 = 255.255.255.0 (256 addresses)
/25 = 255.255.255.128 (128 addresses)
/26 = 255.255.255.192 (64 addresses)
/27 = 255.255.255.224 (32 addresses)
/30 = 255.255.255.252 (4 addresses - common for point-to-point links)

Range

This refers to all the IP addresses that belong to a particular subnet.

Example: 192.168.1.0/24 has a range from:

First address: 192.168.1.0 (network address)
Last address: 192.168.1.255 (broadcast address)
Usable range: 192.168.1.1 through 192.168.1.254 (254 usable host addresses)

Finding Networks Within a Subnet vs. Outside

This is where it gets practical! When you subnet a network, you're creating smaller networks from a larger one.

Example Scenario

You start with 10.0.0.0/8 (a massive network)
You subnet it into /16 networks

Networks WITHIN your subnetting scheme:

10.0.0.0/16
10.1.0.0/16
10.2.0.0/16
...and so on

Each of these is a subnet OF the original /8 network.

Finding if an address is in YOUR subnet

Let's say your device is 172.16.50.100/26

Question: Is 172.16.50.150 in the same subnet?

Quick method:

Your /26 = subnet mask 255.255.255.192
Block size = 256 - 192 = 64
Your subnets increment by 64: .0, .64, .128, .192
Your IP (.100) falls in the .64 to .127 subnet
The .150 address falls in the .128 to .191 subnet
Answer: Different subnets!

Real-World Configuration Example

Router(config)# interface GigabitEthernet0/0
Router(config-if)# ip address 192.168.10.1 255.255.255.0
Router(config-if)# no shutdown

In this config:

IP address: 192.168.10.1
Mask: 255.255.255.0 (also written as /24)
Network: 192.168.10.0/24
Range: .1 through .254 usable
CIDR notation: 192.168.10.0/24

Verification Commands

Router# show ip interface brief
Router# show running-config interface GigabitEthernet0/0

Practice Challenge

Given: 10.20.30.40/28

What's the subnet mask in dotted decimal?
What's the network address?
What's the broadcast address?
How many usable host addresses?
Is 10.20.30.60 in the same subnet?

(Head on over to our skool comunity to see the answers - no judgment, we're all learning!)

Key Takeaway

All these terms are just different ways of describing the same thing - how we divide IP address space into manageable chunks. Mask = the divider, CIDR = the shorthand, Range = the result. Once you see them as connected concepts rather than separate topics, subnetting becomes much clearer.

Next Steps

Practice with different subnet masks. Take any IP/mask combination and work through: What's the network? What's the range? What's usable? Repetition builds mastery!

Have questions about subnetting? Head on over to our skool community to join like minded people all learning their CCNA, post questions and get answers like this one

Below I've included some links to some YouTube videos I've created on subnetting if you want to take this a step further

IPv4 Address Playlist