Network and broadcast addresses
The first and last addresses in the block. Most blocks spend them on the network identifier and the broadcast address, which is why a /24 holds 256 addresses but only 254 hosts.
Subnet calculator
Work out the network and broadcast addresses, the usable host range and the masks for any IPv4 block, and split it into equal subnets. It runs in your browser: nothing you type is sent anywhere.
- CIDR notation
- 10.0.0.0/22
- Netmask
- 255.255.252.0
- Wildcard mask
- 0.0.3.255
- Network address
- 10.0.0.0
- Broadcast address
- 10.0.3.255
- First usable host
- 10.0.0.1
- Last usable host
- 10.0.3.254
- Usable hosts
- 1,022
- Total addresses
- 1,024
- Address type
- Private (RFC 1918)
What each figure means
The four prefixes that behave differently from the arithmetic, and what a router does with each number.
Netmask and wildcard mask
The same prefix written two ways. A netmask marks the network bits with ones; a wildcard mask is its inverse, and is what MikroTik and Cisco access lists match on.
/31 is a point-to-point link
RFC 3021 spends neither address on an identifier, so both ends of the link are usable and there is no broadcast address. It is the right prefix for a router-to-router hop, and halves the addresses a /30 would have burned.
/32 is a single host
One address, and its own network and broadcast. It is what a PPPoE session or a static route to one subscriber is written as.
Address type
Whether the block is public, private (RFC 1918) or carrier-grade NAT (RFC 6598). 100.64.0.0/10 is set aside for CGNAT and is not yours to assign as private space, however much it looks like it.
IPv6 is not supported
This calculator is IPv4 only. IPv6 prefixes are 128 bits and are worked out differently, so the page says so rather than half-answering.