Subnetting Tools

Divide networks efficiently, optimize address allocation, and master network design with our comprehensive subnetting toolkit.

IPv4 Subnet Calculator

Calculate subnet information, network addresses, broadcast addresses, and host ranges with visual network analysis

IPv6 Subnet Calculator

Calculate IPv6 subnets with 128-bit addressing and modern network prefix planning

VLSM Calculator

Variable Length Subnet Mask calculator to break networks into multiple smaller subnets with optimal allocation

Supernet Calculator

Aggregate multiple networks into supernets for route summarization and efficient routing table management

Subnet Planner

Design VLSM networks with drag-and-drop subnet planning and optimize address allocation strategies

What's Subnetting?

Subnetting is the process of splitting a large network into smaller, easier-to-manage pieces. Each subnet has its own network address and range of IPs, which helps organize devices, improve security, and reduce wasted addresses. It's core to network planning (both small home labs, or managing a large office or campus).

These tools aim to make this easier for you, handling the math and planning for you. They calculate network and broadcast addresses, host ranges, and help design or summarize networks so you can focus on building, not IP crunching.

Essential Concepts

Network & Host Bits

The subnet mask determines which bits identify the network vs individual hosts

/24 = 24 network bits, 8 host bits

CIDR Notation

Shorthand for subnet masks using a slash and number of network bits

192.168.1.0/24 instead of 255.255.255.0

Broadcast Domain

Each subnet creates its own broadcast domain, reducing network congestion

Subnet Zero & All-Ones

Modern networks can use all subnets including the first and last ones

Subnetting Techniques

Fixed-Length Subnetting

All subnets use the same mask size. Simple but can waste addresses.

Best for: Equal-sized networks, simple designs

VLSM

Variable-length masks optimize address usage for different subnet sizes.

Best for: Mixed requirements, address conservation

Supernetting

Combine multiple networks into larger blocks for route aggregation.

Best for: Route summarization, BGP optimization

Common Subnet Masks

CIDRSubnet MaskHostsSubnets
/8255.0.0.016,777,2141
/16255.255.0.065,534256
/24255.255.255.025465,536
/25255.255.255.128126131,072
/26255.255.255.19262262,144
/27255.255.255.22430524,288
/28255.255.255.240141,048,576
/29255.255.255.24862,097,152
/30255.255.255.25224,194,304

Best Practices

  • Always plan for growth - allocate more addresses than immediately needed
  • Use /30 networks for point-to-point links to conserve addresses
  • Document your subnet allocation to prevent overlaps
  • Consider using private address space (RFC 1918) for internal networks
  • Plan hierarchically - use summary routes where possible

Common Mistakes

  • Forgetting to account for network and broadcast addresses
  • Using overlapping subnet ranges
  • Not planning for future growth
  • Inconsistent subnet sizing without good reason