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IPv4 subnet calculator: mask, range, CIDR

When setting up an ICS network (PLCs, SCADA, HMIs), you often need to quickly carve up the address space and check whether devices fall in the same subnet. Enter an IP address and prefix — the calculator shows the mask, network address, broadcast address, range, and number of usable hosts.

A 32-bit ruler of the address: network bits from the prefix on the left, host bits on the right — — — — — — — —
Top — the address octets, bottom — the mask octets. Filled bits belong to the network; empty ones are left for hosts.

Input data

Result

Network addressThe first address in the subnet — denotes the network itself. Never assigned to a device. —
Subnet maskThe mask splits the address into a network number and a device number: the mask's ones are the network, the zeros are room for device addresses. —
Wildcard maskThe wildcard mask is the inverse of the regular one (where the mask has 0, this has 1). Needed in access control lists (ACLs) on network equipment, such as Cisco. —
Broadcast addressThe broadcast address — the last one in the subnet. Every device on the network receives packets sent to it; never assigned to a single device. —
First host —
Last host —
Number of hostsHow many devices can connect in this subnet. The network address and the broadcast address don't count. —

How it's calculated

  1. The prefix tells you how many leading bits of the address are reserved for the network number: /24 means 24 ones in the mask, i.e. 255.255.255.0.
  2. The network address comes from a bitwise AND of the address and mask; the broadcast address fills the remaining bits with ones.
  3. All addresses between them can be hosts: the network address and the broadcast address itself are never assigned to devices.

Example: 192.168.1.10/24 → network 192.168.1.0/24, mask 255.255.255.0, broadcast 192.168.1.255. Hosts run from 192.168.1.1 to 192.168.1.254 — 254 in total.

Mask from prefix /n; network = IP AND mask; broadcast = network OR wildcard. Classless addressing — RFC 4632 (CIDR); /31 and /32 — RFC 3021.

This is an estimate

Verify final values against current standards, the project design, and equipment nameplates.

Explained in the article Основы сетей: модель OSI, IP-адреса и кабели

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