IPv4 networks commonly assign the subnet mask 255.255.255.0. Home routers and CCNA certifications often include it.

255.255.255.0 and Subnetting
Subnets split an extensive address range into smaller parts. They lower network traffic and manage access among subnets. A subnet mask shows these splits.
Earlier subnets used classful networks, which grouped IP addresses into five categories (Class A, B, C, D, and E) based on the IP value.
The 255.255.255.0 mask converts to binary as:
- 11111111 11111111 11111111 00000000
The zero bits in the mask represent the subnet’s address range, which covers 8 bits or up to 256 addresses.
The table below shows that smaller subnetworks can be created by adjusting the mask.
Subnet Details for 255.255.255 Prefix
Subnet Mask | Number of Subnets | Hosts Per Subnet |
255.255.255.252 | 64 | 2 |
255.255.255.248 | 32 | 6 |
255.255.255.240 | 16 | 14 |
255.255.255.224 | 8 | 30 |
255.255.255.192 | 4 | 62 |
255.255.255.128 | 2 | 126 |
255.255.255.0 | 1 | 254 |
An incorrectly set subnet mask, called a netmask, might stop you from connecting to the internet.
Subnets and CIDR
The classful system wasted many IP addresses. Large companies and internet providers reserved big address blocks, preventing others from using them.
In the 1990s, developers introduced classless IP networking to allocate addresses more efficiently and meet the growing demand for IPv4 addresses.
Classless networks simplify traditional subnet masks. They use a shorthand based on the count of 1 bit in the mask. Classless Inter-Domain Routing (CIDR) uses this format:
- xxx.xxx.xxx.xxx/n
Here, n is a number from 1 to 31, showing how many 1 bits are in the mask.
CIDR enables classless addressing. It links network masks to IP numbers without relying on their original class.
Routers that support CIDR treat these networks as separate routes, even when they combine multiple traditional subnets.
Network Classes
The InterNIC organization names Internet domains and organizes addresses into different groups called classes. These classes include A, B, and C, which are the most commonly used.
Each class has specific purposes for networking. Class C networks, for example, use a default subnet mask of 255.255.255.0, which helps to divide and manage network connections efficiently.
IP classes are essential in determining how devices communicate within a network.
The structure of these classes allows networks to be scalable and manageable, whether for small networks (Class C), medium-sized networks (Class B), or large-scale networks (Class A).
Can 255.255.255.0 Be Used as an IP Address?
Devices do not use 255.255.255.0 as an IP address, even though it looks like one.
They use it as a subnet mask to define network and device ranges. Subnet masks like 255.255.255.0 help devices separate an IP address into their network and device sections.
The connection will fail if you assign 255.255.255.0 or any IP starting with 255 to a device.
IP networks reserve these ranges for special functions, such as broadcasting or network-specific tasks.