IP Subnet CIDR Calculator
Calculate subnet specifications, network masks, usable IP ranges, hosts count, and binary structures instantly.
⚙️ IP Configurations
📋 Subnetting Outputs
Understanding Classless Inter-Domain Routing (CIDR)
IP Subnetting divides a larger network into smaller, manageable sub-networks (subnets). Historically, networks were divided into Class A, B, and C pools. This was highly inefficient, as assigning a Class B network to an organization that only required 1,000 IPs wasted over 64,000 addresses.
CIDR was introduced in 1993 to replace classful addressing. By appending a slash with a number of routing prefix bits (e.g. /24), networks can be sized precisely. The number tells the router how many bits of the 32-bit IP address represent the network route, leaving the rest to hosts.
Subnet Math Calculations Explained
To find the network address of any IP and mask:
- Convert the IP address and the subnet mask into binary arrays.
- Perform a bitwise logical
ANDoperation between the IP and mask. This zeros out the host portion, resulting in the Network Identifier. - Inverting the subnet mask yields the Wildcard Mask. Performing a bitwise logical
ORbetween the IP and wildcard mask outputs the Broadcast Address.
Frequently Asked Questions
CIDR (Classless Inter-Domain Routing) notation is a compact syntax for representing an IP address and its associated routing prefix. It appends a slash character ('/') followed by a decimal number representing the number of leading 1-bits in the subnet mask (e.g., 192.168.1.0/24).
A /24 subnet provides 256 total IP addresses. Since the first address is reserved for the network identifier and the last address is reserved for the network broadcast address, there are 254 usable host IP addresses (256 - 2).
A wildcard mask is the bitwise inverse of the subnet mask. It is used in Cisco routing access control lists (ACLs) and OSPF configuration to match specific sets of IP addresses. For example, a subnet mask of 255.255.255.0 has a wildcard mask of 0.0.0.255.