Ethical Use Notice
This tool is provided for educational, defensive security, and authorized testing purposes only. Unauthorized access to computer systems, networks, or data is illegal. Always obtain proper authorization before conducting security assessments or testing. Use this tool responsibly and in compliance with all applicable laws and regulations.
Quick CIDR Reference
| CIDR | Subnet Mask | Total Hosts | Description |
|---|---|---|---|
| /32 | 255.255.255.255 | 1 | Single host |
| /31 | 255.255.255.254 | 2 | Point-to-point |
| /30 | 255.255.255.252 | 4 | Point-to-point links |
| /29 | 255.255.255.248 | 8 | Small subnet |
| /28 | 255.255.255.240 | 16 | Very small network |
| /27 | 255.255.255.224 | 32 | Small network |
| /26 | 255.255.255.192 | 64 | Small network |
| /25 | 255.255.255.128 | 128 | Medium network |
| /24 | 255.255.255.0 | 256 | Class C |
| /16 | 255.255.0.0 | 65,536 | Class B |
| /8 | 255.0.0.0 | 16,777,216 | Class A |
Click any row to use that CIDR value
Key Features
Instant Calculations
Real-time subnet calculations as you type. Instantly see network addresses, broadcast addresses, and usable IP ranges.
Complete Network Details
View subnet masks, wildcard masks, CIDR notation, IP classes, total hosts, usable hosts, and binary representations.
One-Click Copy
Easily copy any calculated value to your clipboard with a single click for quick use in network configurations.
IP Type Detection
Automatically identifies private, public, loopback, and link-local IP addresses based on RFC standards.
CIDR Reference Table
Quick reference guide for common CIDR notations with subnet masks and host counts. Click any row to use it.
Binary Conversion
View subnet masks in binary format to understand how network and host bits are divided at the bit level.
Understanding Subnetting
Subnetting is the practice of dividing a network into smaller, more manageable subnetworks. It improves network performance, enhances security, and makes IP address allocation more efficient.
Why Subnet?
- • Reduces broadcast traffic and network congestion
- • Improves network security through segmentation
- • Enables efficient IP address allocation
- • Organizes networks by department, location, or function
- • Simplifies network management and troubleshooting
Common Use Cases
- • Enterprise network design and planning
- • Data center IP allocation
- • Cloud infrastructure configuration (AWS, Azure, GCP)
- • Point-to-point router links
- • VPN and remote access networks
CIDR Notation Explained
CIDR (Classless Inter-Domain Routing) notation provides a flexible method for allocating IP addresses and routing IP packets, replacing the older classful network design.
How CIDR Works
Example: 192.168.1.0/24 means the first 24 bits identify the network
Higher prefix = more network bits = smaller subnet = fewer hosts
Usable hosts = 2^(32-prefix) - 2 (subtract network and broadcast addresses)
Example Breakdown
For 192.168.1.0/24:
- • Network Address: 192.168.1.0
- • Broadcast Address: 192.168.1.255
- • Usable IP Range: 192.168.1.1 - 192.168.1.254
- • Total Hosts: 256 (2^8)
- • Usable Hosts: 254 (256 - 2)
- • Subnet Mask: 255.255.255.0
Private vs Public IP Addresses
Understanding the difference between private and public IP addresses is essential for network design and security planning.
Private IP Ranges (RFC 1918)
10.0.0.0 - 10.255.255.255 (16,777,216 addresses)
172.16.0.0 - 172.31.255.255 (1,048,576 addresses)
192.168.0.0 - 192.168.255.255 (65,536 addresses)
Use Cases:
- • Home networks
- • Corporate LANs
- • Internal servers and devices
- • Behind NAT/firewall
Public IP Addresses
Assigned by Regional Internet Registries (RIRs)
Can be reached directly from the public internet
IPv4 addresses are exhausted, requiring careful management
Use Cases:
- • Web servers
- • Email servers
- • Public-facing services
- • VPN endpoints
Special-Use IP Addresses
Used for local testing (127.0.0.1 = localhost)
APIPA addresses when DHCP fails
Class D addresses for multicast groups
Current network (used in routing)
Frequently Asked Questions
Find answers to common questions
Key Security Terms
Understand the essential concepts behind this tool
MAC Address
A unique hardware identifier assigned to network interfaces for local network communication.
Port Numbers
Numerical identifiers (0-65535) used to route network traffic to specific services on a device.
Subnet Mask
A 32-bit number that divides an IP address into network and host portions for routing.
Penetration Testing
Authorized simulated cyberattacks against systems to identify security vulnerabilities before malicious actors exploit them.
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