How it works

A useful distinction

Subdivision uses more reserved addresses

Splitting a conventional IPv4 /24 into two /25 networks preserves 256 total addresses but reduces ordinary host slots from 254 to 252. Each subnet needs its own network and broadcast addresses; total address count is not usable capacity.

Reading network and address-range results

Choose IPv4 or IPv6 and enter a prefix or supported mask that matches the address family. The result describes how address bits divide into network and host portions under that prefix. Review the specific range labels rather than treating every listed address as an ordinary assignable host. Subnet arithmetic does not verify routing, address ownership, or reachability on a real network.

IPv4 subnet: formula and assumptions

Network = address AND mask; range size = 2^(32−prefix).

/31 follows point-to-point addressing with two usable addresses; /32 identifies one host.

IPv6 subnet: formula and assumptions

Network = address with host bits zeroed; size = 2^(128−prefix).

IPv6 has no broadcast address. The all-zero interface identifier can have special subnet-router-anycast meaning.

IPv4 prefix or dotted mask: formula and assumptions

Contiguous leading mask bits select the network prefix.

Dotted masks are validated before applying the same CIDR arithmetic. /31 uses the explicitly labeled point-to-point convention; /32 represents one host.

Worked example

Using the IPv4 subnet example:

Inputs

IPv4 address: 192.168.1.130
Prefix length: 24

Method

Network = address AND mask; range size = 2^(32−prefix).

Result

Example result

Network: 192.168.1.0/24

Subnet mask: 255.255.255.0

Last address: 192.168.1.255

Broadcast: 192.168.1.255

First usable: 192.168.1.1

Last usable: 192.168.1.254

Usable range: 192.168.1.1 – 192.168.1.254

Total addresses: 256

Usable addresses: 254

These are illustrative inputs. Change the values to explore a different scenario.

Formula references

References explain the underlying methods; they do not imply endorsement or individual professional review of Finflo.

Common questions

Why does an IPv4 /31 show two usable addresses?

The tool explicitly uses the point-to-point convention for /31. A /32 represents a single host address.

Does an IPv6 subnet have a broadcast address?

No. IPv6 does not use a broadcast address. Some address meanings, including subnet-router anycast, need separate interpretation.

Prepared by Finflo. See our methodology and editorial policy.

IP Subnet Calculator

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