IPv4 Subnet Split Calculator

Network	Usable Min	Usable Max	Broadcast	Copy
{{ s.networkAddress }}	{{ s.usableMin }}	{{ s.usableMax }}	{{ s.broadcastAddress }}

Internet address blocks define how devices share a common network and how traffic is routed between neighbors. Splitting a larger block into equal parts helps organize teams and services so that growth is predictable and troubleshooting stays simple.

Subnet planning shows the base range, the first and last usable hosts, and the broadcast for each child block, which makes allocations and change reviews faster. A typical use is to divide a campus range into smaller segments for labs or virtual LANs while keeping room for future moves.

Provide a base address and two mask lengths, then read the summary and the full list of child networks. For example, planning a classroom lab may call for four equal ranges for separate groups so collisions are avoided and resets are quick.

Keep inputs consistent and double check mask order for clean results. Values near boundaries can be tricky, so confirm the first and last host before rollout.

Technical Details:

The topic is Internet Protocol version 4 (IPv4) subnetting. The quantities of interest are the base network address, broadcast address, usable host range, child subnet size, and the number of equal child networks derived from two mask lengths using Classless Inter‑Domain Routing (CIDR).

The computation converts the dotted‑decimal address to a 32‑bit unsigned integer, applies a bit mask from the current mask length, and derives the broadcast by setting host bits. Child subnet size comes from the target mask length. The results matter because they define addressing boundaries that routing and host configuration must respect.

Results are read as ranges. Crossing from one child range into another changes the broadcast and the first and last usable hosts. Values at the edges indicate either the network identifier or the broadcast identifier, which are not assigned to hosts in this model.

Comparisons assume a single IPv4 block at steady state. The approach is arithmetic only and does not infer routing policy, reservations, or device counts.

\begin{matrix} N & = & IP & M \\ B & = & N | ~ M \\ S & = & 2^{32 - L_{new}} \\ K & = & 2^{L_{new} - L} \\ usable per child & = & S - 2 \\ total usable & = & K \cdot S - 2 \end{matrix}

Symbols and units
Symbol	Meaning	Unit/Datatype	Source
IP	Input address	dotted‑decimal	Input
L	Current mask length	integer	Input
L_new	Target mask length	integer	Input
M	Bit mask from L	32‑bit unsigned	Derived
N	Network address	dotted‑decimal	Derived
B	Broadcast address	dotted‑decimal	Derived
S	Child subnet size	integer	Derived
K	Child subnet count	integer	Derived

Worked example: base 192.168.0.1, current /24, target /26.

\begin{matrix} N & = & 192.168.0.0 \\ B & = & 192.168.0.255 \\ S & = & 64 \\ K & = & 4 \end{matrix}

First child range: 192.168.0.0 to 192.168.0.63, usable 192.168.0.1 to 192.168.0.62, broadcast 192.168.0.63.

Units, precision & rounding

All arithmetic uses 32‑bit unsigned integers. No floating‑point rounding is applied. Dotted‑decimal strings are parsed into octets from 0 to 255.

Validation & bounds

Input validation and limits
Field	Type	Min	Max	Step/Pattern	Error Text	Default
IP address	string	0.0.0.0	255.255.255.255	`^(25[0-5]\|2[0-4]\\d\|1?\\d{1,2})(\\.(25[0-5]\|2[0-4]\\d\|1?\\d{1,2})){3}$`	Invalid IPv4 address	192.168.0.1
Current CIDR	integer	1	30	step 1	Current CIDR must be between /1 and /30	24
Target CIDR	integer	L+1	30	step 1	Target CIDR must be larger than current and ≤ /30	26
CSV header	boolean	—	—	switch	—	true
CSV filename	string	—	—	free text	—	subnets.csv

I/O formats

Inputs and outputs
Input	Accepted Families	Output	Encoding/Precision	Rounding
IP address	IPv4 dotted‑decimal	Network, usable min, usable max, broadcast	exact integer arithmetic	not applicable
Mask lengths	integers /1 to /30	Child subnet count and size	powers of two	not applicable
Dataset	—	Tabular view and JSON payload	UTF‑8 text	not applicable

Privacy & compliance

Processing is browser‑based. No data is transmitted or stored on a server. Clipboard copies remain on your device, and downloads are generated locally.

Assumptions & limitations

Arithmetic assumes 32‑bit unsigned representation for all addresses.
Heads‑up Target masks are limited to /30 to preserve host ranges in each child.
Validator accepts octets with one or two digits including leading zero for values below 100.
Input such as 0.0.0.0 and 255.255.255.255 is allowed; interpretation is left to the reader.
Computation does not account for routing policy, reservations, or DHCP scopes.
Very large splits can produce huge tables that may stress the browser.
CSV filename is not validated; the browser decides how the name is handled.
Heads‑up Only IPv4 is supported; IPv6 addressing is out of scope.

Edge cases & error sources

Extra spaces or trailing dots in the address string cause validation failure.
Non‑ASCII digits or mixed numeral systems are not recognized.
Mask lengths outside 1 to 30 are rejected.
Target mask equal to or smaller than current mask is rejected.
Leading zeros with three digits per octet are not accepted.
Browser clipboard permissions may block copying in restricted contexts.
Generating millions of rows can freeze the tab; reduce the split size.
Copying very large JSON may be truncated by clipboard managers.
Locale settings do not affect parsing; only dots separate octets.
Network and broadcast addresses are not included in usable host counts.

Scientific & standards backing

The behavior aligns with IPv4 addressing practice and CIDR representation. Integer bit‑masking follows conventional binary arithmetic on 32‑bit values.

How‑to Guide

IPv4 subnet splitting yields equal child ranges from a base network for structured allocations.

Enter the base address e.g., 192.168.0.1.
Choose the current mask length e.g., /24.
Choose a larger target mask length e.g., /26.
Review the summary and the list of child networks.
Check first and last usable hosts before assigning.

Example: /24 to /26 yields four equal ranges of 64 addresses each, with 62 usable hosts per child.

Apply the chosen range to devices or VLANs and keep the rest for future growth.

FAQ

Is my data stored?

No. All calculations and copies occur on your device. Nothing is sent to a server.

Clipboard content remains local to your system.

How accurate is the split?

It is exact integer arithmetic on 32‑bit values. Network and broadcast are computed by masking and setting host bits deterministically.

Which formats are supported?

Inputs are IPv4 dotted‑decimal addresses and integer mask lengths. Outputs include a table view and a JSON representation of inputs and results.

Can I use /31 or /32?

No. Masks are limited to /1 through /30 to retain a usable host range in each child subnet.

Does it work without a connection?

Yes. Computation runs in the browser. Copy and download features depend on standard browser capabilities.

What does “larger target mask” mean?

A larger mask length has more leading ones in the mask, which creates more but smaller child subnets.

How many child subnets will I get?

The count is 2 to the power of the difference between target and current mask lengths.

Why are first and last addresses special?

The first is the network identifier and the last is the broadcast identifier, so neither is assigned to hosts in this model.

Glossary

IPv4: Internet Protocol version 4 with 32‑bit addressing.
CIDR: Classless mask notation using a length such as /24.
Network address: The first address in the block with host bits cleared.
Broadcast address: The last address in the block with host bits set.
Usable host range: Addresses between network and broadcast for assignment.
Subnet size: The total address count within a child subnet.
Mask length: The count of leading ones that defines the block.
Dotted‑decimal: Four octets separated by dots such as 192.168.0.1.