Enter an IP address with a CIDR prefix or netmask to get the network and broadcast addresses, usable host range, counts, wildcard mask, and binary breakdown. Everything runs in your browser. Nothing is sent anywhere.
Enter an IPv4 address and a prefix (for example 24 or /24) or a dotted netmask (for example 255.255.255.0). Results update as you type.
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A subnet mask splits an IP address into a network portion and a host portion. In CIDR notation the prefix length (for example /24) states how many leading bits identify the network. A /24 is the same as the netmask 255.255.255.0 and leaves 8 bits, or 254 usable host addresses, for devices.
The netmask marks the network bits with ones (255.255.255.0). The wildcard mask is its inverse, marking the host bits with ones (0.0.0.255). Wildcard masks are used in access control lists and routing configurations, such as Cisco ACLs and OSPF.
A normal subnet reserves the first address for the network and the last for broadcast, so usable hosts equal total addresses minus two. A /31 has only two addresses and, under RFC 3021, both are usable for point-to-point links. A /32 is a single host route with exactly one address.
No. All calculations run entirely in your browser using local JavaScript math. Nothing you type is transmitted or stored.