IP CIDR Subnet Calculator
Calculate IP ranges, subnets, and network boundaries from CIDR notation. Visually split blocks and check IP range matches in real-time.
CIDR Notation
Range Membership Checker
Instantly test if a specific IP address is routed inside the active CIDR block boundaries.
Recent Queries
Network Boundaries
Binary Allocation Display
Subnet Splitter & Explorer
Divide your primary CIDR block into smaller sub-networks. Select your target prefix boundaries and filter/search matches in real-time. You can load any sub-network as your parent CIDR to drill down.
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IP CIDR Subnet Calculator Guide & FAQs
Understanding IP Subnetting & CIDR Notation
Classless Inter-Domain Routing (CIDR) is the standard method used to allocate IP addresses and route Internet Protocol packets. An IP address consists of 32 bits, divided into four 8-bit octets separated by dots (e.g., 192.168.1.1). In CIDR notation, a routing prefix is appended to the IP address with a slash (e.g., /24), indicating the number of bits allocated to the network portion of the address.
The remaining bits are allocated for host addresses. For example, in a /24 subnet, 24 bits are reserved for the network, leaving 8 bits for hosts (32 - 24 = 8). The total number of IP addresses in this block is 28 = 256. However, two addresses in every subnet are reserved: the network address (all host bits set to 0) and the broadcast address (all host bits set to 1). Therefore, the number of usable host IPs is 254 (2(32-prefix) - 2).
Calculating Subnet Allocations
Subnetting allows network administrators to divide a large network block into smaller, more manageable subnets. Our calculator provides visual sub-splitting, allowing you to drag, merge, and split blocks interactively. By utilizing binary math on the IP octets, you can quickly find the range, mask, gateway, and host capacities without manually translating binary strings.
Frequently Asked Questions
What is CIDR?
Classless Inter-Domain Routing (CIDR) is a method for allocating IP addresses and IP routing. It replaced the older system based on Class A, B, and C networks, allowing for much more flexible and efficient address allocation.
How do you calculate subnet size from prefix?
The size of a subnet is calculated using the formula 2^(32 - prefix). For example, a /28 subnet has 32 - 28 = 4 host bits, resulting in 2^4 = 16 total IP addresses (14 of which are usable for devices).
What are the network and broadcast addresses?
The network address is the first address in a subnet block and identifies the network itself. The broadcast address is the last address in the block and is used to send data to all hosts on the subnet. Neither address can be assigned to a host device.