Network Design StudioPublic beta

Engineering tools / IP address design / multiple segments

VLSM planning

Design multiple right-sized subnets within one parent network. Enter each network and its device count, then see an automatically packed address plan. Everything stays in your browser.

1. Describe the site
Try a sample plan, then adjust the requirements.

Use a real network boundary such as 192.168.10.0/24. The planner will never allocate outside this block.

What is VLSM and why use it?

Variable Length Subnet Masking allocates different-size subnet blocks from one larger network. The biggest needs are placed first, helping reduce wasted space. This planner only models conventional LAN segments—not point-to-point /31s, cloud-specific reserved addresses or live equipment settings.

2. Add network segments
Each row represents a separate group of devices.
Segment 1
Segment 2
Segment 3

The planner supports up to 30 segments. Use the device count that should fit on each LAN; it calculates IPv4 network and broadcast reservations.

3. Review your address plan

Automatic, largest-first network allocation; no router configuration is generated.
All segments fit

Parent addresses

256

Allocated addresses

208

Unallocated addresses

48

  • Staff network

    192.168.10.0/25

    Devices
    100
    Usable addresses
    126
    Host range
    192.168.10.1 – 192.168.10.126

  • Cameras

    192.168.10.128/26

    Devices
    50
    Usable addresses
    62
    Host range
    192.168.10.129 – 192.168.10.190

  • Guest Wi-Fi

    192.168.10.192/28

    Devices
    10
    Usable addresses
    14
    Host range
    192.168.10.193 – 192.168.10.206

Exports mark complete/incomplete status and retain any segments that could not be allocated; do not treat a partial plan as deployable. The free-address count includes any gaps caused by alignment; not every free address is necessarily one contiguous allocatable range. Check gateways, DHCP reservations and cross-site conflicts separately.

How to use this safely

VLSM design is derived from CIDR arithmetic. Confirm that a VLAN or routed interface exists for every segment, assess DHCP pool size, reserved device addresses and future growth, and verify there are no overlapping routes elsewhere. This page does not inspect or change real networks.

RFC 4632: CIDR address assignment