CIDR Network Tools
Formula Used
CIDR notation joins an address with a prefix length. The prefix identifies network bits and remaining host bits. This calculator exposes both portions for easier network planning.
| Calculation | Formula |
|---|---|
| IPv4 network | IP address AND subnet mask |
| IPv4 broadcast | Network address OR wildcard mask |
| Total IPv4 addresses | 232 − prefix |
| Total IPv6 addresses | 2128 − prefix |
| Traditional usable hosts | Total addresses − 2 |
| Required subnet prefix | Original prefix + ceiling(log2(subnets)) |
How to Use
Choose a tool and enter the requested network values. Select address rules before running subnet or range calculations. Review warnings carefully before applying changes to production networks.
- Select analysis, subnetting, VLSM, aggregation, range, testing, or batch mode.
- Enter IPv4 or IPv6 values using accepted CIDR notation.
- Choose traditional, point-to-point, or all-address counting rules.
- Submit the form and review validation messages.
- Copy results or export CSV and PDF reports.
Example Data
| Task | Example input | Expected result |
|---|---|---|
| IPv4 analysis | 192.168.1.10/24 | Network 192.168.1.0/24 |
| IPv6 analysis | 2001:db8::1234/64 | Network 2001:db8::/64 |
| Subnet generation | 192.168.0.0/24 to /26 | Four /26 subnets |
| VLSM planning | 10.0.0.0/24 with 100, 50, 25 | Descending fitted subnets |
| Range conversion | 192.168.1.10 to 192.168.1.99 | Minimum CIDR cover |
Prefix Reference
| Prefix | Subnet mask | Total addresses | Traditional usable hosts |
|---|---|---|---|
| /8 | 255.0.0.0 | 16,777,216 | 16,777,214 |
| /16 | 255.255.0.0 | 65,536 | 65,534 |
| /20 | 255.255.240.0 | 4,096 | 4,094 |
| /22 | 255.255.252.0 | 1,024 | 1,022 |
| /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 |
| /31 | 255.255.255.254 | 2 | 0 |
| /32 | 255.255.255.255 | 1 | 1 |
Frequently Asked Questions
What does CIDR mean?
CIDR means Classless Inter-Domain Routing. It replaces rigid address classes with flexible prefixes. Prefixes let networks use address space more efficiently today.
What does a slash prefix represent?
The slash number counts fixed network bits. Larger prefixes leave fewer bits for host addresses. Smaller host sections create fewer addresses per subnet overall.
How are usable IPv4 hosts calculated?
Traditional subnets exclude network and broadcast addresses. Point-to-point networks can use both addresses inside a /31. Select the mode matching your operational routing requirements carefully.
Does IPv6 use broadcast addresses?
IPv6 does not use traditional broadcast addresses. Multicast and neighbour discovery replace many broadcast functions. The calculator therefore shows first and last addresses clearly.
What is a wildcard mask?
A wildcard mask is the inverse subnet mask. Access control lists often use wildcard bit patterns. Each zero requires matching while each one ignores differences.
What is VLSM?
VLSM means Variable Length Subnet Masking. It assigns different subnet sizes to different requirements. Larger requirements should receive address blocks before smaller ones.
Can adjacent networks always be aggregated?
Adjacent ranges must align on valid binary boundaries. Equal-sized neighbouring blocks often combine into shorter prefixes. The aggregation tool also reports unavoidable additional addresses clearly.
Why does the calculator normalise my network?
An entered address may contain nonzero host bits. CIDR networks begin at their calculated network boundary. Normalisation prevents accidental routes covering unexpected address ranges later.
What does overlap mean?
Two networks overlap when their address ranges intersect. One network may also fully contain another network. Overlaps can cause route, firewall, or allocation conflicts quickly.
How does range conversion work?
The converter covers the requested range using CIDRs. It chooses the largest aligned block at each step. This produces a minimal exact list without extras included.
Can I process multiple CIDR blocks?
Batch mode accepts one CIDR block per line. It validates, sorts, detects duplicates, and checks overlaps. IPv4 entries can also be merged into fewer blocks.