Allocation Table
| Subnet Name | Hosts Needed | Allocated Size | Network Address | CIDR | Range | Broadcast |
|---|
Visual Block Diagram
A visual representation of how the IP space is divided relative to the major network.
About Variable Length Subnet Masking (VLSM)
Welcome to the Advanced VLSM Calculator. This tool is designed to help network engineers, students, and IT professionals design efficient network schemas without the headache of manual binary math. By using Variable Length Subnet Masking, you can allocate IP addresses more efficiently than traditional classful subnetting.
How It Works
Traditional subnetting applies a single mask (like 255.255.255.0) to an entire network, which wastes addresses if you have subnets of vastly different sizes (e.g., a LAN with 100 users vs. a point-to-point WAN link with 2 IPs).
VLSM solves this by allowing you to "subnet a subnet." Our algorithm works by:
- Sorting: Taking your requested subnets and automatically ordering them from largest to smallest (host count). This is critical to ensure the math aligns correctly on binary boundaries.
- Allocating: Assigning the smallest power-of-two block that fits your requirement (plus Network & Broadcast IDs).
- Calculating: Determination of the specific Network ID, Broadcast ID, and valid Host Range for each block smoothly.
How to Use This Tool
- Enter Major Network: Input your starting block in CIDR format (e.g.,
10.0.0.0/16). - Add Subnets: List the segments you need (Marketing, Sales, WAN Links) and how many usable IPs each requires.
- Calculate: Hit the button to generate your table and visual map.
- Export: Use the "Export CSV" feature to save your plan for documentation.
Tips & Best Practices
- Always leave room for growth. If a department has 40 users, don't request exactly 40. The next block size up is 64 (62 usable). If you request 60, you'll still get a /26 block, but if you expect to hit 70 users soon, consider requesting 70 to force a larger allocation (128 block) if address space permits.
- Don't forget overhead. Every subnet uses 2 addresses: one for the Network ID (first) and one for the Broadcast IP (last). This calculator handles that automatically.
- WAN Links: For point-to-point router connections, you typically need 2 IPs. VLSM allows you to use a /30 subnet (4 addresses total) rather than wasting a whole /24.
Frequently Asked Questions (FAQ)
What is the difference between FLSM and VLSM?
FLSM (Fixed Length Subnet Mask) uses the same mask for all subnets, leading to wasted space. VLSM uses the most efficient mask for each specific subnet.
Why are my subnets reordered?
The calculator reorders subnets from largest to smallest host count. This is a mathematical requirement for efficient packing of subnets without gaps or overlaps.
Is this calculator client-side?
Yes. All calculations happen instantly in your browser. No network data is sent to any server, ensuring your network plans remain private and secure.
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