VLAN Planner & IP Address Plan Generator

Generated VLAN plan

A snippet is available only after the plan passes validation.

Worked example: four /24 VLANs from 10.20.0.0/22

Choose IPv4 FLSM, enter 10.20.0.0/22, select /24, and use four rows. Each /24 contains 256 total addresses and 254 traditional usable host addresses.

Parent utilization: 4 × 256 / 1,024 = 100%. The first subnet is 10.20.0.0/24; the last is 10.20.3.0/24. Leave a larger parent or deliberate gaps if the site needs future VLANs.

Subnet sizing and allocation guidance

For IPv4, required capacity is ceil(DHCP hosts × (1 + growth margin)) + max(static hosts + gateway, low exclusion) + high exclusion. The planner then selects the smallest prefix whose traditional usable capacity, 2^(32 − prefix) − 2, meets that total. A /26 has 62 usable addresses; a /24 has 254. Size for leases, infrastructure, static devices, exclusions, and growth—not just today’s device count.

Sequential allocation keeps site blocks contiguous and usually produces the clearest summary route. Growth gaps trade address efficiency for easier expansion. Even distribution is useful when separating future functional groups, but it can create more specific routes. VLSM always evaluates larger requirements first so a small early subnet cannot fragment space needed by a later large subnet.

IPv6 mode uses IPv6 semantics: /64 per VLAN by default, no broadcast address, no IPv4 usable-host subtraction, and no IPv4 DHCP-pool arithmetic. The displayed ::1 router address is a convention to review, not an IPv6 requirement.

Import, export, and configuration formats

CSV import columns: vlanId,name,purpose,requiredHosts,prefix,requestedSubnet,gatewayMode,customGateway,dhcpPolicy,customDhcpRange,staticHosts,owner,notes. The header is required; unrecognised columns are ignored. CSV and JSON exports include calculated masks, wildcard, capacity, static range, DHCP range, broadcast, and validation status. Print / PDF uses the browser’s print dialog. Local save uses this browser’s local storage.

Vendor snippets are intentionally available only after a conflict-free plan. They are documentation starters, not complete switch, routing, relay, firewall, or VRF configurations.

Methodology, limits, and test vectors

Supported inputs: IPv4 parent prefixes /0 through /30 and child prefixes through /30; IPv6 parent prefixes /0 through /127 with /64 VLANs by default. VLAN IDs are checked from 1 through 4094. IPv4 host addresses in a parent or requested CIDR are rounded down by applying the prefix mask, and the correction is shown. Host-driven IPv4 demand is rounded up before prefix selection.

Validation: the planner checks duplicate VLAN IDs, CIDR boundaries, blocks outside the parent, subnet overlap, gateway membership, required capacity, DHCP membership, DHCP/static overlap, and parent exhaustion. Automatically allocated rows are ordered largest-first in VLSM. Manual subnets remain fixed and are checked before automatic allocation.

Known limits: it does not query an IPAM, detect addresses used elsewhere, model IPv4 /31 point-to-point rules, model IPv6 SLAAC/DHCPv6 lease behavior, configure equipment, or prove route reachability. Distributed allocation is deterministic but is a planning aid, not an optimizer for an existing route table.

CIDR and IPv4 aggregation follow RFC 4632; private IPv4 examples follow RFC 1918; DHCP terminology follows RFC 2131; IPv6 addressing follows RFC 4291 and RFC 8200; VLAN tagging is standardised by IEEE 802.1Q. Last technically reviewed: 15 July 2026.

VLAN planning FAQs

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.