VLSM Worksheets
Generate custom Variable Length Subnet Mask (VLSM) practice worksheets with answer keys. Perfect for networking students learning efficient IP address allocation. Practice allocating subnets of different sizes from a single network block.
Worksheet Settings
Each version will have 2 different problems.
Worksheet Preview
Note: The PDF will include all worksheet versions followed by all answer keys.
How to Use the VLSM Worksheet Generator
- Choose number of versions: Select how many different worksheet versions you need (1-26, labeled A-Z).
- Select subnets per problem: Choose between 3-6 subnets or random for variety.
- Choose parent network size: Select Class C (/24), Class B (/16), or any size for mixed practice.
- Generate: Click "Generate Worksheets" to create your VLSM problems.
- Download PDF: Save the worksheets with answer keys as a PDF file.
What is VLSM?
Variable Length Subnet Mask (VLSM) is a technique that allows network administrators to divide an IP address space into subnets of different sizes. This optimizes IP address usage by allocating appropriately sized subnets based on actual requirements.
Key Concepts
- Efficient allocation: Assign subnet sizes that closely match the number of required hosts, minimizing wasted addresses.
- Largest first: Allocate largest subnets first to ensure all requirements can be met within the parent network.
- No overlap: Subnets must not overlap - each subnet gets a unique, contiguous address range.
- Sequential allocation: Subnets are allocated sequentially from the parent network to avoid fragmentation.
How to Solve VLSM Problems
- List requirements: Write down all subnet requirements with their host counts.
- Sort by size: Arrange requirements from largest to smallest number of hosts.
- Calculate subnet sizes: For each requirement, determine the subnet mask needed (2^n - 2 ≥ required hosts).
- Allocate sequentially: Starting from the parent network address, allocate each subnet in order.
- Calculate addresses: For each subnet, determine network address, broadcast address, and usable range.
- Verify no overlap: Ensure each subnet starts where the previous one ended (broadcast + 1).
Features
✓ Multiple Versions
Generate up to 26 different worksheet versions (A-Z) for classroom use.
✓ Answer Keys Included
PDF includes both worksheets and complete answer keys with all calculations.
✓ Realistic Problems
Problems use realistic subnet requirements found in real networks.
✓ Complete Tables
Each problem includes a table for network, broadcast, netmask, and usable hosts.
✓ Customizable Difficulty
Choose number of subnets and parent network size to match skill level.
✓ One Problem Per Page
Each problem gets its own page with ample space for calculations.
VLSM Calculation Tips
- Powers of 2: Memorize 2^1 through 2^16 for quick subnet size calculations.
- Host formula: Usable hosts = 2^(32 - CIDR) - 2 (subtract network and broadcast addresses).
- Round up: Always round up to the next power of 2 when calculating required subnet size.
- Check available space: Ensure the parent network has enough addresses for all required subnets.
- Binary visualization: Understanding binary helps see how subnet boundaries align.
- Block size: The subnet size (total addresses) tells you where the next subnet begins.
- Verify calculations: Last address of one subnet + 1 = first address of next subnet.
Common Use Cases
- CCNA preparation: VLSM is a core skill tested on Cisco CCNA certification exam.
- Network+ study: Essential topic for CompTIA Network+ certification.
- Network design: Practice real-world IP addressing scenarios for efficient network design.
- Classroom exercises: Teachers can generate unique problems for each student.
- Homework assignments: Students can practice unlimited problems with instant verification.
- Skills assessment: Test understanding of subnet allocation and optimization.
- Interview preparation: Common topic in networking technical interviews.
Example Problem
Given: Parent Network 192.168.1.0/24
Requirements:
- Subnet A: 50 hosts
- Subnet B: 25 hosts
- Subnet C: 10 hosts
Solution Steps:
- Sort by size: A (50), B (25), C (10)
- Calculate required masks: A needs /26 (62 hosts), B needs /27 (30 hosts), C needs /28 (14 hosts)
- Allocate Subnet A: 192.168.1.0/26 (192.168.1.0 - 192.168.1.63)
- Allocate Subnet B: 192.168.1.64/27 (192.168.1.64 - 192.168.1.95)
- Allocate Subnet C: 192.168.1.96/28 (192.168.1.96 - 192.168.1.111)
Frequently Asked Questions
How many problems are on each worksheet?
Each worksheet version contains 2 VLSM problems, with each problem on its own page for clarity and working space.
What should I fill in the table?
For each subnet row, calculate and fill in: Network Address (with CIDR), Broadcast Address, Subnet Mask (decimal notation), and Total Usable Hosts.
Why sort subnets largest to smallest?
Allocating largest subnets first ensures you have space for all requirements. If you allocate small subnets first, you may fragment the address space and not have contiguous blocks for larger subnets.
What if requirements don't fit in the parent network?
The generator ensures all requirements will fit. In real scenarios, you'd need a larger parent network or reduce subnet requirements.
Should I leave unused address space?
Yes, in real networks you allocate only what's needed. VLSM problems will often have unused addresses in the parent network after all subnets are allocated.
