VLSM Calculator

Allocate Variable Length Subnet Masks (VLSM) from a major base network block (e.g. `192.168.1.0/24`) based on individual department host requirements (e.g. Sales 50 hosts, IT 20 hosts, HR 10 hosts). Minimizes IP address waste.

Why Use This Tool?

• Efficient IP Allocation: Allocate subnets of varying sizes from a single base block without wasting IP addresses.
• Corporate Network Design: Design subnets tailored to exact department headcount requirements.
• Cisco & CCNA Exam Preparation: Solve complex VLSM subnetting problems with step-by-step table outputs.

How to Use

1. Enter Base Network IP and CIDR prefix (e.g. `10.0.0.0/24`).
2. Add Subnet Names and Required Host counts (e.g. Dept A: 60, Dept B: 25, Dept C: 10).
3. View generated VLSM allocation table showing Subnet CIDR, Mask, Usable Range, and Broadcast IP.

Real Working Example

Input:

Base Network: 192.168.1.0/24 | Requirements: Engineering (100 hosts), Sales (50 hosts), Admin (10 hosts)

Output Result:

Engineering: 192.168.1.0/25 (126 usable hosts)
Sales: 192.168.1.128/26 (62 usable hosts)
Admin: 192.168.1.192/28 (14 usable hosts)

Important Technical Details & Standards

• Largest-First VLSM Allocation Algorithm: Sorts host requirements in descending order to allocate largest subnets first, preventing address fragmentation.
• Unallocated Space Tracking: Displays remaining unallocated IP addresses in the base network.
• Client-Side Engine: Fast calculation in local browser memory.

Related Networking & Security Tools

• IPv4 Subnet Calculator: Calculate subnets and netmasks.
• CIDR Aggregator: Merge adjacent CIDR blocks.
• IPv4 Range Expander: Convert IP ranges to CIDR.