VLSM Calculator
Calculate Variable Length Subnet Masking (VLSM) allocations. Optimize network allocation by assigning different subnet sizes based on specific host requirements.
Enter the number of hosts needed for each subnet, one per line. Will be sorted largest to smallest.
Allocation Results
ALLOCATION EFFICIENCY
2750.00%
TOTAL ALLOCATED
4
SUBNETS CREATED
4
| Network | CIDR | Netmask | Needed | Available | First Host | Last Host | Broadcast |
|---|---|---|---|---|---|---|---|
| 10.0.0.0 | /32 | 255.255.255.255 | 50 | 1 | 10.0.0.0 | 10.0.0.0 | 10.0.0.0 |
| 10.0.0.1 | /32 | 255.255.255.255 | 30 | 1 | 10.0.0.1 | 10.0.0.1 | 10.0.0.1 |
| 10.0.0.2 | /32 | 255.255.255.255 | 20 | 1 | 10.0.0.2 | 10.0.0.2 | 10.0.0.2 |
| 10.0.0.3 | /32 | 255.255.255.255 | 10 | 1 | 10.0.0.3 | 10.0.0.3 | 10.0.0.3 |
What is VLSM?
Variable Length Subnet Masking (VLSM) allows you to partition a network into subnets of different sizes, optimizing IP address allocation.
Instead of dividing a network into equal-sized subnets, VLSM creates subnets based on actual host requirements, reducing wasted IP addresses.
How It Works
1. Sort requirements (largest first)
2. Calculate minimum CIDR for each
3. Allocate sequential subnets
4. Display allocation efficiency
Common Use Cases
Campus networks with varying departments
ISP network allocation
Enterprise IP planning
Branch office subnet design
Example
Network: 10.0.0.0/16
Hosts needed: 50, 30, 20, 10
→ 10.0.0.0/25 (126 hosts)
→ 10.0.0.128/26 (62 hosts)
→ 10.0.0.192/27 (30 hosts)
→ 10.0.0.224/28 (14 hosts)