How does this VLAN IP plan generator choose subnets?

It starts at the parent network address and creates equal-size, sequential IPv4 subnets using the selected child prefix. It does not skip around for route summarization beyond the parent block.

Can I use first or last usable address as the gateway?

Yes. Choose first usable, last usable, or a custom usable-host offset for the default gateway in each generated subnet.

How are DHCP ranges calculated?

The DHCP range starts after the low reserved address count and ends before the high reserved address count. The gateway is removed from the DHCP count if it falls inside that range.

Does this tool support IPv6 or variable-size subnets?

No. This page generates equal-size IPv4 VLAN subnets. IPv6 and VLSM-style mixed prefix plans need different assumptions.

Is this VLAN planner private?

Yes. Inputs are processed locally in your browser and are not sent to a backend.

VLAN and IP Address Plan Generator

Generate an IPv4 VLAN plan from one parent CIDR block. The table includes VLAN IDs, names, subnets, masks, usable ranges, default gateways, DHCP ranges, DHCP pool sizes, and broadcast addresses.

All calculations run locally in your browser. Validate production changes against IPAM, routing, DHCP, firewall, and change-control records.

Inputs

Parent IPv4 network Network address for the parent block, such as 10.20.0.0.

Parent prefix

VLAN subnet prefix

Number of VLANs

VLAN labels

Starting VLAN ID

VLAN ID step

VLAN name prefix Rows use this as the prefix, for example SITE-A-100.

Gateway and DHCP rules

Gateway address

Custom gateway offset 1 means first usable, 2 means second usable.

Low reserved usable addresses Reserve addresses at the start for gateway, VIPs, switches, printers, and static hosts.

High reserved usable addresses Reserve addresses at the end for static assignments or future use.

Plan presets

Results

Plan status-

Generated VLANs-

Parent utilization-

DHCP addresses-

Parent block

Normalized parent CIDR:-

Parent address count:-

VLAN subnet size:-

Maximum equal-size VLANs:-

Unused equal-size subnets:-

Per-VLAN usable hosts:-

Generated VLAN plan

VLAN	Name	Subnet	Netmask	Usable range	Gateway	DHCP range	DHCP size	Broadcast
Generate a plan to populate the table.

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How to use this VLAN IP address planner

Enter the parent CIDR: use the address block you own for this site, campus, lab, or environment.
Pick the child prefix: select the subnet size every generated VLAN should use.
Set VLAN numbering: choose the first VLAN ID, step, and naming prefix.
Choose gateway and DHCP rules: reserve low and high usable addresses before generating DHCP pools.
Export the result: copy or download the table for IPAM, firewall, DHCP, or change planning.

Formula and assumptions

Addresses per subnet: 2^(32 - prefix)

Traditional usable hosts: addresses per subnet - 2 for /16 through /30, reserving the network and broadcast addresses.

Maximum equal-size VLANs: 2^(child prefix - parent prefix)

Sequential subnet: parent network + row index x child subnet size

DHCP range: first usable + low reserve through last usable - high reserve, with the gateway removed from the DHCP count if it falls inside that span.

CIDR prefix notation and address block sizes follow the IPv4 CIDR model described in RFC 4632. Private address examples use the ranges reserved by RFC 1918. DHCP lease behavior is not modeled here; use the DHCP Scope Calculator for lease-time sizing.

Example VLAN planning scenarios

Scenario	Common subnet size	Planning note
Office user VLANs	/24 or /23	Leave room for phones, docking stations, and transient devices if the VLAN also supports Wi-Fi or guest access.
Infrastructure management VLANs	/26 or /25	Reserve predictable low addresses for gateways, switch management, controllers, monitoring, and out-of-band systems.
Lab or staging networks	/27 to /24	Small subnets reduce blast radius, but frequent rebuilds may need larger DHCP pools.
Campus or building blocks	/23 or larger	Keep contiguous blocks per site when route summarization and troubleshooting simplicity matter.

Methodology

The generator parses the parent IPv4 block, normalizes it to the selected prefix boundary, then allocates equal-size child subnets in ascending order. For each VLAN it calculates the network address, broadcast address, first and last usable address, default gateway, netmask, wildcard mask, and DHCP pool. It warns when the requested VLAN count exceeds the parent block, when VLAN IDs would exceed 4094, or when reservation rules leave no DHCP addresses.

Last reviewed: June 2026. This tool is for IPv4 planning and does not configure network equipment.

FAQs

Should every VLAN use the same subnet size?

No. Equal-size subnets are simple and easy to summarize, but real networks sometimes need variable-size subnetting. Use this tool for consistent site blocks, then adjust special cases in IPAM.

Why does the parent network get normalized?

CIDR blocks start on binary boundaries. If you enter an address inside a block, the tool shows the actual network address for that prefix so the generated subnets stay aligned.

Can I use this output directly in production?

Use it as a planning aid. Confirm routing, firewall zones, DHCP scopes, relay interfaces, DNS, monitoring, NAC, and IPAM ownership before implementation.

What VLAN ID range is supported?

The form validates normal VLAN IDs from 1 through 4094. Reserved, native, voice, management, and provider VLAN conventions still depend on your environment.

Is this planner private?

Yes. Inputs are processed locally and are not submitted to a backend.

Disclaimer

This is an infrastructure planning aid. Review address ownership, route summarization, DHCP failover, security segmentation, and operational change-management requirements before applying a VLAN or IP address plan in production.