If you’ve ever set up a router, configured a server, or looked at your network settings, you’ve seen numbers like 255.255.255.0 or /24 without knowing exactly what they mean. Those are subnet masks — and understanding them demystifies a huge chunk of how the internet actually works.
This guide explains what a subnet is, why subnets exist, and how to read subnet notation — all without needing a networking degree.
What Is a Subnet?
A subnet (short for subnetwork) is a smaller network carved out of a larger one. Think of it like this: if a city is a network, then individual neighborhoods are subnets. Every house in the neighborhood shares the same street name (network address) but has its own house number (host address).
In networking terms, every device on the internet has an IP address. An IP address has two parts: the network portion (which neighborhood you’re in) and the host portion (your specific address within that neighborhood). A subnet defines exactly where the boundary between those two parts falls.
Why Do Subnets Exist?
Subnets were invented to solve a very practical problem: IPv4 address exhaustion. There are only about 4.3 billion possible IPv4 addresses, which sounds like a lot until you realize every smartphone, laptop, server, router, and smart device needs one.
Subnetting lets organizations take one large block of IP addresses and divide it into smaller, more manageable chunks. A company might receive a single /16 block (65,536 addresses) and then subnet it into hundreds of /24 blocks (254 usable hosts each) for different departments, buildings, or functions.
Subnets also improve network performance and security. Traffic within a subnet stays local and doesn’t need to be routed through the wider internet. Firewalls can be applied at subnet boundaries to control which networks can talk to each other.
Reading Subnet Notation
You’ll encounter subnets written in two ways:
CIDR Notation
CIDR stands for Classless Inter-Domain Routing. It looks like this: 192.168.1.0/24
The number after the slash (24) tells you how many bits are used for the network portion. Since an IP address is 32 bits total, /24 means 24 bits are network, 8 bits are host. That gives you 2≫ = 256 total addresses, or 254 usable hosts (the first is the network address, the last is the broadcast address).
Subnet Mask Notation
The same /24 subnet written as a mask is 255.255.255.0. Each 255 represents 8 bits all set to 1, and the 0 represents 8 bits all set to 0 (the host portion). Where the mask has 1s = network. Where it has 0s = hosts.
Common Subnet Sizes at a Glance
- /8 (255.0.0.0) — 16,777,214 usable hosts. Used for very large networks like 10.0.0.0/8 (the largest private range).
- /16 (255.255.0.0) — 65,534 usable hosts. Common for enterprise networks and the 172.16.0.0/12 private range.
- /24 (255.255.255.0) — 254 usable hosts. The most common subnet for home and small business networks. 192.168.1.0/24 is what most home routers use.
- /28 (255.255.255.240) — 14 usable hosts. Common for small server clusters or dedicated VLAN segments.
- /30 (255.255.255.252) — 2 usable hosts. Used for point-to-point links between routers.
- /32 — Single host. Used to identify one specific IP address in routing tables.
Private vs Public Subnets
Not all subnets are reachable from the public internet. There are three reserved private IP ranges that can be used freely inside any organization:
- 10.0.0.0/8 — Class A private range
- 172.16.0.0/12 — Class B private range
- 192.168.0.0/16 — Class C private range (your home network is almost certainly in here)
These addresses never appear on the public internet. Your home router uses Network Address Translation (NAT) to translate between your private subnet and your single public IP address.
The Network Address and Broadcast Address
Every subnet has two special addresses that cannot be assigned to devices:
Network address: The first address in the range. For 192.168.1.0/24, the network address is 192.168.1.0. It identifies the subnet itself and appears in routing tables.
Broadcast address: The last address in the range. For 192.168.1.0/24, it’s 192.168.1.255. Packets sent to the broadcast address go to every device on the subnet simultaneously.
Everything in between — 192.168.1.1 through 192.168.1.254 — can be assigned to actual devices. That gives you 254 usable host addresses for a /24 subnet.
Subnetting in Practice: Your Home Network
Right now, your home router is almost certainly running a 192.168.1.0/24 or 192.168.0.0/24 subnet. Your router is typically at 192.168.1.1 (the default gateway), and every device on your network gets an address somewhere between .2 and .254 via DHCP.
Want to see your own network details? Use the ExamineIP Subnet Calculator — enter your IP and mask and it will show your network address, broadcast, host range, wildcard mask, and binary representation instantly.
What Is Subnet Splitting?
Splitting a subnet means dividing it into smaller equal-sized subnets. Each time you add one bit to the prefix, you double the number of subnets and halve the hosts per subnet.
For example, splitting a /24 into two subnets gives you two /25 networks. Each /25 has 126 usable hosts. Splitting into four gives four /26 networks with 62 hosts each.
This is how large organizations allocate IP space: they receive a large block and subdivide it for different departments, floors, or services — keeping traffic segmented for security and performance.
IPv6 and Subnetting
With IPv6, subnetting works the same way conceptually but at a completely different scale. A standard IPv6 allocation is a /64 — that single subnet contains more addresses than the entire IPv4 internet has total. IPv6 was designed specifically so that address exhaustion would never be a problem again.
Tools to Help You Calculate Subnets
You don’t need to do subnet math in your head. The ExamineIP Subnet Calculator handles all of it instantly:
- Network and broadcast addresses
- First and last usable hosts
- Subnet mask and wildcard mask
- Binary representation of all key values
- Subnet splitting into smaller networks
- Full CIDR reference table (/0 through /32)
Check your current IP and network details
See what IP address you’re currently using and which ISP or network it belongs to: tools.examineip.com
Frequently Asked Questions
What is the difference between a subnet and a VLAN?
A subnet is a Layer 3 (IP) concept — it defines IP address ranges. A VLAN (Virtual Local Area Network) is a Layer 2 concept that logically separates devices on the same physical switch. In practice they’re often paired: each VLAN gets its own subnet, and a router or Layer 3 switch routes between them.
Is 192.168.1.1 the same as 192.168.1.0/24?
No. 192.168.1.0/24 is the network (the whole subnet). 192.168.1.1 is a specific host address within that subnet — typically your router’s default gateway address.
Can I subnet my home network?
Yes, but it’s rarely necessary for a standard home network. Subnetting becomes useful if you want to segment IoT devices from your main devices, or if you run a home lab with VLANs on a managed switch.