Symptom: 192.168.1.0/24 looks cryptic
Configuring servers, container networks, or a cloud VPC, you keep meeting 10.0.0.0/16, 192.168.1.0/24. What does that number after the slash mean?
What CIDR is
CIDR (Classless Inter-Domain Routing) writes a network as IP/prefix-length. For 192.168.1.0/24:
- An IPv4 address is 32 bits;
/24means the first 24 bits are the network portion, the remaining 8 bits are host portion;- The subnet mask is
255.255.255.0(24 binary 1s).
Devices sharing the network bits are on the same subnet and can talk directly; crossing subnets needs a gateway.
How to compute usable addresses
| Item | Calculation |
|---|---|
| Host bits | 32 - prefix length |
| Total addresses | 2 ^ host bits |
| Usable hosts | 2 ^ host bits - 2 (minus network and broadcast) |
Common prefixes:
| CIDR | Mask | Usable hosts |
|---|---|---|
| /24 | 255.255.255.0 | 254 |
| /16 | 255.255.0.0 | 65534 |
| /8 | 255.0.0.0 | 16777214 |
Common pitfalls
- Subtract 2 for usable: beginners often use
2^8 = 256, but the first and last addresses can't be assigned to hosts; - Network address: all host bits 0 (e.g.
192.168.1.0) denotes the segment itself; - Broadcast address: all host bits 1 (e.g.
192.168.1.255) is for broadcast; - /31, /32 special: point-to-point links and single-host have dedicated uses; don't worry daily.
How to compute with a tool
Open the Subnet Calculator or CIDR Calculator on ToolVault:
- Enter an IP and prefix (e.g.
192.168.1.100/24); - The tool shows network address, broadcast address, usable range, and mask;
- Change the prefix to see segment size change live — no manual math.
Computed locally.
FAQ
Are /24 and 255.255.255.0 the same?
Yes, just two notations. /24 is the prefix-length form; 255.255.255.0 is dotted-decimal mask — both say "first 24 bits are network".
Why are home routers usually /24?
A /24 gives 254 usable addresses — plenty for home devices, yet not so large it's unmanageable.
Must subnetting and mask always match?
They must. The mask defines "which bits are network"; CIDR's /N is just shorthand for the mask.
Provided by ToolVault. Related tools: Subnet Calculator, CIDR Calculator, Dockerfile Generator. Visit the home page for more developer tools.