TECH TOOL / 04
Subnet calculator.
Less subnet math. More clarity.
Try an example
YOUR NETWORK
- First host
- Last host
- Subnet mask
- Wildcard mask
- Network / host bits
This classifies the entered IP only. A wide subnet can include multiple address types. This tool does not scan devices or check internet reachability.
See the binary breakdown
IPv4 has 32 bits. The prefix sets the network bits; the remaining bits identify addresses within that network.
Network bitsHost bits
- IP address
- Subnet mask
Network = address AND subnet mask. Wildcard = inverse of the subnet mask.
PLAN SMALLER NETWORKS
Split this subnet.
Choose a longer prefix to create equal-size subnets.
| Subnet | First host | Last host | Usable hosts |
|---|
START WITH THE CAPACITY
How many hosts?
Find the smallest subnet for a conventional IPv4 LAN, reserving one network and one broadcast address. This is capacity math; it does not account for gateways or other addresses you need to reserve.
For ordinary LAN sizing the smallest suggestion is /30. /31 is for compatible point-to-point links; /32 describes a single address.
Common IPv4 prefixes
| Prefix | Subnet mask | Total | Usable |
|---|
CIDR, masks, and the /31–/32 exceptions
CIDR: /24 means the first 24 of 32 bits are network bits. That leaves 8 host bits and 2⁸ = 256 addresses.
Subnet mask: 255.255.255.0 represents the same /24 prefix. A valid mask has consecutive 1 bits followed by consecutive 0 bits.
Wildcard: 0.0.0.255 is the inverse of a /24 mask. Some access-control rules use this notation.
/31: On compatible point-to-point links, both addresses can be used (RFC 3021); there is no subnet-directed broadcast. This differs from an ordinary LAN.
/32: One specific IPv4 address, commonly used in host routes. There is no separate network or broadcast reservation.
IPv6: This calculator covers IPv4 only. IPv6 has different address and broadcast conventions.