In an address such as 192.168.1.10/24, the /24 means the first 24 bits form the network prefix. The corresponding mask is 255.255.255.0, and the subnet spans 192.168.1.0 through 192.168.1.255.
Key takeaways
- A larger CIDR number creates a smaller address block.
- Traditional subnets reserve the network and broadcast addresses.
- /31 point-to-point networks and /32 host routes are special cases.
What a CIDR prefix means
An IPv4 address contains 32 bits. The CIDR number after the slash states how many leading bits belong to the network prefix. The remaining bits identify addresses within that block.
A /24 leaves eight address bits, giving 2⁸ or 256 total addresses. A /28 leaves four address bits, giving 16 total addresses.
| Prefix | Subnet mask | Total addresses | Traditional usable hosts |
|---|---|---|---|
| /24 | 255.255.255.0 | 256 | 254 |
| /25 | 255.255.255.128 | 128 | 126 |
| /26 | 255.255.255.192 | 64 | 62 |
| /27 | 255.255.255.224 | 32 | 30 |
| /28 | 255.255.255.240 | 16 | 14 |
| /29 | 255.255.255.248 | 8 | 6 |
| /30 | 255.255.255.252 | 4 | 2 |
Network, host range, and broadcast
The network address is the first address in a traditional subnet and identifies the block. The broadcast address is the last and reaches all hosts on that broadcast domain. Addresses between them form the traditional usable host range.
For 192.168.1.10/24, the network address is 192.168.1.0, the broadcast address is 192.168.1.255, and the traditional host range is 192.168.1.1 through 192.168.1.254.
How the mask finds the network
A bitwise AND operation between the IP address and subnet mask produces the network address. Combining that network with the inverted mask produces the broadcast address. A calculator performs these binary steps without hiding what each result means.
Special cases: /31 and /32
A /31 contains two addresses and is commonly used on point-to-point links where traditional network and broadcast reservations are unnecessary. Both addresses can represent endpoints in that context.
A /32 identifies exactly one IPv4 address. It is commonly used as a host route or to refer to one specific endpoint.
Subnetting checks that prevent mistakes
Before applying a subnet, verify both the address count and the operational context.
- Count current and expected endpoints.
- Allow room for infrastructure addresses where required.
- Check that ranges do not overlap.
- Confirm gateway and DHCP boundaries.
- Document the CIDR prefix with every network address.
Use the numbers
Related calculators
Common questions
Questions, answered.
Does a larger prefix mean more hosts?+
No. A larger prefix uses more bits for the network and leaves fewer bits for addresses, so the block becomes smaller.
How many addresses are in a /24?+
A /24 has 256 total addresses and traditionally 254 usable host addresses.
Is 255.255.255.0 the same as /24?+
Yes. That subnet mask contains 24 leading one bits, so it is written as /24 in CIDR notation.