Purpose and steps
CIDR Calculator validates ipv4/prefix before applying the displayed equation. Only IPv4 is supported. /31 has no conventional broadcast address on a point-to-point link.
- Determine the IPv4 network, mask, last address and address count from a prefix. For /31 the host count follows the point-to-point convention; /32 represents one address.
- Enter IPv4/prefix in the stated format. Baseline values are for reproduction.
- Check the output unit and convention: Read network with its stated unit and convention. The default example and the independent worked scenario use different inputs, so compare the assumptions before comparing the numbers.
- Change one input and compare the result. Only IPv4 is supported. /31 has no conventional broadcast address on a point-to-point link. VLSM planning, IPv6, network discovery and device configuration are not included.
Input reference and units
These values reproduce the model’s demonstration. Replace them with your own records or measurements; they are not recommended targets.
On a small screen, swipe the table horizontally to see all columns.
| Parameter | Demonstration value | How to enter it |
|---|---|---|
| IPv4/prefix | 192.168.1.10/24 | Enter ipv4/prefix without adding a unit suffix. Scope: Only IPv4 is supported. /31 has no conventional broadcast address on a point-to-point link. |
Model-specific method
How this calculator produces its result
CIDR Calculator: size = 2^(32−prefix); network = floor(address/size) × size. Input definitions: cidr = IPv4/prefix. Use the selected convention throughout the calculation.
CIDR Calculator: calculation relationships
Determine the IPv4 network, mask, last address and address count from a prefix. For /31 the host count follows the point-to-point convention; /32 represents one address. Only IPv4 is supported. /31 has no conventional broadcast address on a point-to-point link. VLSM planning, IPv6, network discovery and device configuration are not included.
CIDR combines an IPv4 address and prefix in one string. The host portion of 192.0.2.5/31 is rounded down to the aligned network 192.0.2.4; the block contains .4 and .5. RFC 3021 permits both on a point-to-point link. That convention is not a promise that any device or broadcast network accepts the configuration.
size = 2^(32−prefix); network = floor(address/size) × size
- cidr: IPv4/prefix. Enter ipv4/prefix without adding a unit suffix. Scope: Only IPv4 is supported. /31 has no conventional broadcast address on a point-to-point link.
- Result units: stated beside each output
- Calculation relationship: size = 2^(32−prefix); network = floor(address/size) × size
- Supported domain: see the limits below
Worked example
CIDR Calculator baseline input: IPv4/prefix: 192.168.1.10/24. Output: Network = 192.168.1.0; Subnet mask = 255.255.255.0; Last address = 192.168.1.255; Address count = 256; Usable hosts (RFC 3021 for /31) = 254. Substitute these values into the displayed equation to reproduce the result.
Reproduce the default scenario
This reproduces the default inputs in the reference table above; it is not an additional independent example. Displayed rounding may differ from intermediate precision.
- Network
- 192.168.1.0
- Subnet mask
- 255.255.255.0
- Last address
- 192.168.1.255
- Address count
- 256
- Usable hosts (RFC 3021 for /31)
- 254
Reading results without overstating them
- Read network with its stated unit and convention. The default example and the independent worked scenario use different inputs, so compare the assumptions before comparing the numbers.
- Change one input at a time and use the equation to explain the result; do not mix unit, grade-scale, time-zone or rounding conventions across comparisons.
Assumptions and exclusions
- Only IPv4 is supported. /31 has no conventional broadcast address on a point-to-point link.
- VLSM planning, IPv6, network discovery and device configuration are not included.
Sources and content notes
Toolify describes the implemented algorithm and its assumptions. Sources below support the topic or applicable rules; they do not endorse this calculator. Examples are illustrative, and published rules take precedence over simplified estimates.
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