Calculate network ranges, subnet masks, broadcast addresses, first/last usable IP coordinates, and wildcard masks instantly. Optimized with real-time binary bitmask layouts to help network engineers and system administrators structure robust networks.
CIDR (Classless Inter-Domain Routing) is an IPv4 addressing scheme that replaced the old Classful network architecture (Class A, B, and C). By introducing flexible routing prefixes (e.g. /24, /27, /19), CIDR allows networks to be allocated at exact power-of-two sizes matching actual resource requirements, saving billions of unused IPv4 addresses from going to waste.
In any IP network block, the first address (where all host bits are binary 0) is reserved as the Network Identifier, which routers use to find the destination network. The last address (where all host bits are binary 1) is the Broadcast Address, used to send a packet to every host in that subnet simultaneously. Assigning either to a specific physical device would break standard IP stack routing protocols.
RFC 1918 sets aside three distinct blocks of IPv4 addresses for private local area networks (LANs) that are never routed on the public internet: Class A (10.0.0.0 to 10.255.255.255), Class B (172.16.0.0 to 172.31.255.255), and Class C (192.168.0.0 to 192.168.255.255). Devices on these ranges use Network Address Translation (NAT) to access the public web.
A subnet mask uses consecutive binary 1s to identify the network portion of an IP address (e.g., 255.255.255.0). A wildcard mask is essentially the inverse (bitwise NOT) of the subnet mask, where 0 bits must match exactly and 1 bits are 'don't care' wildcards (e.g., 0.0.0.255). Wildcard masks are widely used in router Access Control Lists (ACLs) and OSPF routing configurations.
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