CIDR · netmask · IPv6 prefix
Subnet calculator
Enter an address with a prefix length or netmask to get the network and broadcast addresses, the usable host range and masks, a bit-by-bit view and a list of smaller subnets. IPv6 prefixes work too.
Reading the results
A prefix length says how many leading bits name the network; the rest number the hosts. A /24 has 8 host bits, so 256 addresses. The first address is the network and the last is the broadcast, which leaves 254 usable hosts. The binary view shows exactly where the line between network and host bits falls.
- Netmask and wildcard are the same boundary written two ways; wildcards are used in router access lists and OSPF.
- /31 networks have no broadcast address, so both addresses are usable on point-to-point links (RFC 3021). A /32 is a single host.
- Scope tells you whether the range is public, private (RFC 1918), carrier-grade NAT, documentation or another special-purpose block.
- Split divides the network into equal smaller subnets; the first 256 are listed and the full list can be copied as CSV.
For IPv6 the calculator shows the network, its fully expanded form, the last address, the number of /64 networks it holds and the matching ip6.arpa zone for reverse DNS. Everything is calculated on your device.
Frequently asked questions
How many usable hosts does a /24 have?
254. It has 256 addresses, minus the network address and the broadcast address.
Why do IPv6 networks use /64?
Stateless address autoconfiguration (SLAAC) needs a 64-bit interface identifier, so a LAN segment is normally a /64. Sites usually receive a /48 or /56, which holds 65,536 or 256 of them.
What is the difference between a netmask and a wildcard mask?
A wildcard mask is the netmask with every bit flipped: 255.255.255.0 becomes 0.0.0.255. Netmasks mark the network bits, wildcards mark the bits that may vary.