IP Subnet Calculator

CIDR (Classless Inter-Domain Routing) notation combines an IP address with a prefix length: 192.168.1.0/24. The /24 means the first 24 bits are the network portion, leaving 8 bits for hosts (256 addresses, 254 usable). It replaced the old Class A/B/C system.

The first address in a subnet is the network address (identifies the subnet itself), and the last is the broadcast address (used to send traffic to all hosts). Both are reserved and cannot be assigned to individual devices.

A subnet mask divides an IP address into network and host portions. It uses ones to mark the network bits and zeros for host bits. For example, 255.255.255.0 means the first 24 bits identify the network (192.168.1) and the last 8 bits identify individual hosts (1-254).

Private ranges (10.0.0.0/8, 172.16.0.0/12, 192.168.0.0/16) are for internal networks and don't route on the public internet. Public IPs are globally unique and routable. The subnet calculator works with both, but private ranges are the most common use case.

A wildcard mask is the inverse of the subnet mask - it specifies which bits are variable. It's primarily used in Cisco ACLs (Access Control Lists) and OSPF routing configurations. Wildcard = 255.255.255.255 - subnet mask.