What does CIDR notation mean?
CIDR expresses the number of network bits after an address, such as /24. The remaining bits identify hosts within that network range.
Relevant standard: RFC 4632 — Classless Inter-domain Routing (CIDR)
NETWORK DIAGNOSTICS
IPv4 CIDR and subnet calculator.
Calculate IPv4 network ranges, subnet and wildcard masks, broadcast addresses, usable host ranges and binary network bits.
Leave the first netmask empty to use the traditional default for Class A, B or C. Wildcard masks such as 0.0.0.255 are accepted. This local calculator has no per-IP or usage limits.
What this IP calculator shows
This IPv4 CIDR calculator converts an address and subnet mask into the network address, broadcast address, usable host range, host count and Cisco wildcard mask.
Use the optional second mask to calculate subnets or supernets. The binary view marks the network bits and host bits so you can see how the prefix length changes an address range.
Frequently asked questions
Technical context and standardsWhat are the network and broadcast addresses?
For a conventional IPv4 subnet, the network address has all host bits set to zero and the broadcast address has all host bits set to one. The calculator derives both from the address and mask.
Relevant standard: RFC 950 — Internet Standard Subnetting Procedure
Which IPv4 ranges are private?
The private IPv4 ranges are 10.0.0.0/8, 172.16.0.0/12 and 192.168.0.0/16. They are intended for internal networks and are not globally routed on the public Internet.
Relevant standard: RFC 1918 — Address Allocation for Private Internets
Why does a /31 show two usable addresses?
On a point-to-point IPv4 link, both addresses in a 31-bit prefix can be used without a broadcast address. This is a specific exception for point-to-point links.
Relevant standard: RFC 3021 — Using 31-Bit Prefixes on IPv4 Point-to-Point Links