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CIDR Calculator

Calculate network ranges, subnet masks, and IP address information from CIDR notation

Network Information

How to Use the CIDR Calculator

Getting Started

  • Step 1: Enter any IP address within the network you want to analyze
  • Step 2: Specify the CIDR prefix length (subnet mask bits)
  • Step 3: Click "Calculate CIDR" to get complete network information
  • Step 4: Review network address, broadcast address, and host counts

Key Concepts

  • CIDR Notation: Combines IP address with prefix length (e.g., 192.168.1.0/24)
  • Network Address: First IP in the subnet, identifies the network
  • Broadcast Address: Last IP in the subnet, used for broadcasting
  • Subnet Mask: Defines which bits represent network vs host portions

Best Practices

  • Subnetting: Use appropriate prefix lengths for network size requirements
  • Address Planning: Reserve network and broadcast addresses
  • Documentation: Record CIDR blocks for network management
  • Overlap Prevention: Ensure subnet ranges don't overlap

Network Guidelines

  • /24 Networks: Standard for small LANs (254 usable hosts)
  • /16 Networks: Medium networks (65,534 usable hosts)
  • /8 Networks: Large networks (16,777,214 usable hosts)
  • Private Ranges: Use RFC 1918 ranges for internal networks

Frequently Asked Questions

What does CIDR stand for and why is it important?

CIDR (Classless Inter-Domain Routing) is a method for allocating IP addresses and routing. It replaced the older classful network system and allows for more efficient use of IP address space by using variable-length subnet masks.

How do I choose the right CIDR prefix length?

Choose based on the number of hosts needed. /24 gives 254 usable hosts, /25 gives 126, /26 gives 62, etc. Each reduction in prefix length halves the available hosts but doubles the number of possible subnets.

What's the difference between network and broadcast addresses?

The network address (first IP) identifies the subnet itself and cannot be assigned to hosts. The broadcast address (last IP) is used to send packets to all hosts in the subnet. Both are reserved and not usable for host assignment.

Can I use any IP address in CIDR calculations?

Yes, you can enter any IP address within the network. The calculator will determine the correct network and broadcast addresses based on the CIDR prefix, regardless of which specific IP you enter from that subnet.

What are private IP address ranges?

RFC 1918 defines private ranges: 10.0.0.0/8 (10.0.0.0 to 10.255.255.255), 172.16.0.0/12 (172.16.0.0 to 172.31.255.255), and 192.168.0.0/16 (192.168.0.0 to 192.168.255.255). These are not routed on the internet.

How does subnetting help with network organization?

Subnetting divides large networks into smaller, manageable segments. This improves security by isolating traffic, reduces broadcast domains, enables better network organization, and allows for more efficient IP address allocation.

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