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IP Subnet Calculator
Network Planning Made Simple

Professional IP subnet calculator for network engineers and IT professionals. Calculate subnets, CIDR notation, usable hosts, and design efficient network architectures.

Network engineers
VLSM support
IPv4 subnetting

IP Subnet Calculator

Analyze IP addresses, subnet masks, and create subnets

Understanding IP Subnetting

Learn the fundamentals of IP addressing and subnet design.

What is a Subnet?
A subnet divides an IP network into smaller segments. This improves security, reduces traffic, and allows efficient IP address allocation.
CIDR Notation
Classless Inter-Domain Routing uses slash notation (e.g., /24) to specify the number of network bits in the subnet mask.
Subnet Masks
A 32-bit number that separates network and host portions of an IP address. Common masks: 255.255.255.0 (/24), 255.255.0.0 (/16).
Private IP Ranges
RFC 1918 defines private ranges: 10.0.0.0/8, 172.16.0.0/12, and 192.168.0.0/16. These are not routable on the public internet.
VLSM
Variable Length Subnet Masking allows different subnet sizes within the same network, optimizing IP address usage.
Network Planning
Proper subnetting improves network performance, simplifies management, and enhances security through segmentation.

Common Subnet Reference

Small Networks

  • /30 = 2 usable hosts
  • /29 = 6 usable hosts
  • /28 = 14 usable hosts
  • /27 = 30 usable hosts
  • /26 = 62 usable hosts

Medium Networks

  • /25 = 126 usable hosts
  • /24 = 254 usable hosts
  • /23 = 510 usable hosts
  • /22 = 1,022 usable hosts
  • /21 = 2,046 usable hosts

Large Networks

  • /20 = 4,094 usable hosts
  • /16 = 65,534 usable hosts
  • /12 = 1M+ usable hosts
  • /8 = 16M+ usable hosts
  • Class A, B, C ranges

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