CIDR Calculator
Calculate subnet masks, IP ranges, and network addresses
Input
CIDR Notation
Calculation Options
Results
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Enter CIDR notation and click "Calculate CIDR" to get started
Quick Reference
Common prefix lengths: /8 (16.7M hosts), /16 (65K hosts), /24 (254 hosts), /28 (14 hosts), /30 (2 hosts)
When to Use CIDR Calculator
Network Planning
Plan network infrastructure by calculating subnet sizes, IP ranges, and addressing schemes for optimal resource allocation
Security Configuration
Configure firewalls, access control lists, and security policies by determining exact IP ranges and subnet boundaries
Troubleshooting
Diagnose network connectivity issues by verifying IP addressing, subnet membership, and routing configurations
Learning & Education
Study networking concepts, subnetting principles, and IP addressing schemes for certification exams and courses
Cloud Computing
Design VPCs, subnets, and network architectures for cloud platforms like AWS, Azure, and Google Cloud
Enterprise Networks
Design and manage large-scale enterprise networks with complex subnetting and addressing requirements
Frequently Asked Questions
What is CIDR notation?
CIDR (Classless Inter-Domain Routing) notation is a method for specifying IP addresses and their associated routing prefix. It's written as IP_ADDRESS/PREFIX_LENGTH, where the prefix length indicates how many bits are used for the network portion. For example, 192.168.1.0/24 means the first 24 bits are the network address, leaving 8 bits for host addresses.
How do I calculate subnet mask from CIDR?
To calculate subnet mask from CIDR notation: 1) Take the prefix length (e.g., /24), 2) Create a 32-bit binary number with that many 1s followed by 0s (e.g., 11111111.11111111.11111111.00000000), 3) Convert each 8-bit group to decimal (e.g., 255.255.255.0). The calculator automatically performs this conversion and shows both binary and decimal representations.
What is the difference between network address and broadcast address?
The network address is the first address in a subnet and identifies the network itself (all host bits are 0). The broadcast address is the last address in a subnet and is used to send data to all hosts in the network (all host bits are 1). For example, in 192.168.1.0/24, the network address is 192.168.1.0 and the broadcast address is 192.168.1.255.
How many usable IP addresses are in a subnet?
The number of usable IP addresses in a subnet is calculated as 2^(32-prefix_length) - 2. The '-2' accounts for the network address and broadcast address which cannot be assigned to hosts. For example, a /24 subnet has 2^(32-24) - 2 = 256 - 2 = 254 usable addresses.
What are common CIDR prefix lengths?
Common CIDR prefix lengths include: /8 (Class A, 16.7M addresses), /16 (Class B, 65K addresses), /24 (Class C, 254 addresses), /28 (16 addresses), /30 (4 addresses, often used for point-to-point links), and /32 (single host). The choice depends on the number of hosts needed and network design requirements.
How do I determine if two IP addresses are in the same subnet?
To determine if two IP addresses are in the same subnet: 1) Apply the subnet mask to both addresses using bitwise AND operation, 2) Compare the resulting network addresses, 3) If they match, the addresses are in the same subnet. Our calculator can help verify this by showing the network address for any given IP and CIDR notation.
What is VLSM (Variable Length Subnet Masking)?
VLSM allows different subnets to have different subnet mask lengths within the same network. This enables more efficient use of IP address space by creating subnets of varying sizes based on actual host requirements. CIDR notation supports VLSM by allowing any prefix length from /0 to /32.
How accurate is the CIDR calculator?
Our CIDR calculator provides accurate results based on standard IP addressing and subnetting principles. It handles all valid IPv4 addresses and CIDR prefix lengths from /0 to /32. The calculations follow RFC standards for IP addressing and are suitable for network planning, troubleshooting, and educational purposes.
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