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CIDR / Subnet Calculator

Ranges, masks and host counts.

IPv4 and IPv6. A range (start - end) is split into the fewest CIDR blocks.
Runs in your browser

About the CIDR / Subnet Calculator

This calculator takes an IPv4 or IPv6 block and shows its network address, broadcast address, first and last usable host, host counts, netmask, wildcard mask and the bits in binary. It also says what kind of space the block is: private (RFC 1918), carrier-grade NAT (100.64.0.0/10), loopback, link-local, multicast, documentation ranges, unique local IPv6 (fc00::/7) or public.

You can type a block in CIDR notation (10.0.0.0/8), an address with a netmask (192.168.1.10 255.255.255.0, Cisco wildcard masks work too) or a range (10.0.0.1 - 10.0.0.50). A range is converted into the fewest CIDR blocks that cover it exactly.

How to use it

  1. Type or paste an address, block, netmask or range. Results update as you type.
  2. If the address has host bits set, the calculator shows the network it belongs to.
  3. Check whether an IP is inside the block, or split the block into smaller subnets (the table lists up to 256 and gives the total).

Examples

Common questions

Why does a /24 have 254 usable hosts, not 256?

In IPv4 the first address names the network and the last one is the broadcast address, so neither is given to a host. A /31 is the exception: on point-to-point links both addresses are usable (RFC 3021), and a /32 is a single host.

Does IPv6 have a broadcast address?

No. IPv6 uses multicast instead, so every address in a prefix can be assigned. The all-zero address is the Subnet-Router anycast address, which most networks leave to the router.

What is a wildcard mask?

The inverse of the netmask, used in Cisco ACLs and OSPF: 0.0.0.255 matches the same addresses as 255.255.255.0.