Subnet Calculator

Learn how CIDR prefix length determines IPv4 network boundaries and how IPv6 prefixes identify the size of a network block.

IPv4 network address

The subnet mask determines which bits belong to the network portion of an IPv4 address. Applying the mask to the IP address produces the network address.

Broadcast and hosts

For an IPv4 subnet, the broadcast address is the highest address in the block. Traditional usable-host counts exclude the network and broadcast addresses, although /31 and /32 have special uses.

CIDR notation

A prefix such as /24 means 24 of the 32 IPv4 bits belong to the network prefix. A shorter prefix represents a larger address block.

IPv6 prefixes

IPv6 uses 128-bit addresses. A prefix such as /64 identifies the first 64 bits as the network prefix, leaving the remainder for interface addressing.

Practical uses

Subnet calculations help with network planning, address allocation, routing and troubleshooting.

Limitations

Real network designs can use special-purpose ranges, routing policies and provider allocations that require more context than a mathematical subnet calculation.