CIDR notation describes how many leading bits identify a network prefix. A subnet calculator applies that prefix to an address so you can review the network boundary and address range before using it in a plan or change.
The number after the slash is the prefix length: how many high-order bits belong to the network. For IPv4, a /24 leaves 8 host bits and contains 256 total addresses. For IPv6, the same /24 leaves 104 host bits; prefix sizes must be interpreted within their address family.
For ordinary IPv4 subnets, the first address identifies the network and the last is the directed-broadcast address; traditional host ranges exclude both. /31 is commonly used for point-to-point links, and /32 represents one address. Confirm your routing and platform conventions before assigning addresses.
An IPv4 ACL wildcard mask is the bitwise inverse of a contiguous subnet mask. For example, 255.255.255.0 becomes 0.0.0.255, commonly used to match a /24 range in router ACLs. Syntax and matching behavior vary by platform, so confirm the vendor's documentation before applying a rule. The local calculator displays both values.
An IPv6 prefix defines an inclusive range by clearing host bits for the start and setting them for the end. IPv6 does not use broadcast addresses. The calculator shows range endpoints and an exact address count; it does not decide which addresses to allocate or how your network routes them.
The single-range calculators do not compare a proposed network with other ranges. The local CIDR overlap checker compares up to 64 IPv4/IPv6 ranges you enter and flags intersections within the same address family. It cannot see reserved allocations, cloud routes, VPNs or customer address plans; compare results against authoritative IP address management and routing records, then review the change with the network owner.
Subnet calculations and overlap comparisons happen in your browser and make no network request. IPv4 returns the canonical network, mask, endpoint and broadcast values. IPv6 returns a canonical network prefix, inclusive start/end range and exact count. The overlap checker compares only the ranges you provide, with a maximum of 64 entries; it does not check DNS, routing, connectivity, address ownership, reservations or external networks.
Choose the matching address family and enter the address and prefix. Use the overlap checker when you have a proposed list of networks. Review results against your authoritative plan before assigning or changing routes.
