How a subnet mask works
An IP address consists of two parts: the network number and the host number within it. The mask shows where the boundary lies. In CIDR notation 192.168.1.0/24 the number after the slash is how many bits belong to the network: 24 network bits leave 8 bits for hosts, i.e. 256 addresses.
What the calculator shows
- Network address and broadcast — the first and last addresses of the range, which are not assigned to devices in IPv4.
- Host range — the addresses you can assign to servers, routers and computers.
- Wildcard mask — the inverted mask used in Cisco router access lists and OSPF.
- Subnetting — how to split an allocated block into smaller ones, e.g. a /24 into four /26s for different VLANs.
/31 networks (RFC 3021) are used for point-to-point links, so both of their addresses are usable. IPv6 has no broadcast, and the standard subnet size for end devices is /64.