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The profile sets the candidate range before reservations and existing assignments are removed.
Use commas, spaces, or semicolons; ranges such as 1002-1005 are accepted.
Duplicates are counted once; overlaps with reserved IDs are flagged for review.
Whole segments from 0 to 100,000; demand above the pool is reported as a shortfall.
Whole host addresses from 1 to 10,000,000 for each new segment.
The growth reserve is rounded up to a whole host address.
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Choose /1 through /30; point-to-point /31 behavior is outside this endpoint-segment check.
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Normal first prefers IDs through 1001; extended first prefers IDs from 1006 upward.
The neutral default is 0; growth headroom remains based on the endpoint count.
Capacity plan
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Calculation method:
The same canonical values feed the summary, guidance, chart, ledger, and exports.
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Planning guidance
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The chart renderer is unavailable. The capacity plan and ledger remain available.

OrderVLAN IDRangePlanned hostsSubnet fitCopy
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DHCP Scope Calculator Size an IPv4 DHCP scope from real pool ranges and peak demand, then test policy choices against growth and target headroom before deployment.
ACL Wildcard Mask Calculator Calculate IPv4 ACL wildcard masks from CIDR and dotted entries, then audit generated lines for address coverage and dangerous overlaps.
IPv4 Allocation Planner Allocate IPv4 subnets in an ordered parent CIDR, with exact usable ranges and checks for VLSM fit, alignment gaps and remaining space.
VLAN Config Consistency Checker Compare switch VLAN evidence with intended trunk and native rules plus database, reserved-VLAN, and VLAN 1 policy before a change.

A new network segment needs two different kinds of room. It needs an unused VLAN identifier on the switching fabric, and it usually needs an IP subnet large enough for the devices that will join it. Plenty of address space does not repair an exhausted VLAN pool, while hundreds of unused VLAN IDs do not make a small subnet fit more hosts.

VLAN ledgers become hard to trust when reservations, active assignments, and future requests are mixed together. A number held for infrastructure or migration is unavailable even if no switch currently reports it in use. An assignment outside the planning range may be real, but it should not consume capacity in the lane being reviewed. Duplicates should count once, and an ID that appears in both the reserved and existing lists needs reconciliation rather than double subtraction.

QuestionEvidenceFailure to avoid
Is an ID available?Selected VLAN range minus reserved and existing IDsReusing an ID or approving more segments than the lane can hold
Will each subnet fit?Endpoint demand, infrastructure addresses, growth allowance, and IPv4 prefixAssigning a VLAN whose subnet runs out of usable host addresses
Will the platform carry it?Switch, trunk, VTP, and local allocation policyTreating every mathematically valid ID as operationally usable

The broad configurable span is VLAN 1 through 4094, but hardware and policy can narrow it. Cisco terminology commonly separates the normal range, 1 through 1005, from the extended range, 1006 through 4094. VLAN 1, legacy defaults such as 1002 through 1005, and platform-internal allocations are common reasons to reserve IDs. The actual switch estate remains the authority because supported counts and internally consumed IDs vary.

IPv4 sizing adds a separate limit. A prefix describes a power-of-two address block, but ordinary endpoint subnets normally lose the network and broadcast addresses. This model therefore treats a /24 as 254 usable host addresses and restricts the check to /1 through /30. Point-to-point /31 behavior is deliberately outside its endpoint-segment assumptions.

Capacity planning is a proposal, not a configuration audit. Confirm the final ID queue against the live VLAN database, trunk allow-lists, spanning-tree design, gateway plan, DHCP reservations, and change records before deployment.

How to Use This Tool:

Start with the VLAN lane that the change is allowed to use, then account for exclusions before testing new demand.

  1. Choose VLAN range profile. Use the enterprise profile when IDs 2 through 4094 are eligible, or select the full, normal, or extended lane only when it matches the platform policy.
  2. Enter Reserved VLAN IDs and Existing VLAN IDs. Separate IDs or ranges with commas, spaces, or semicolons; a range such as 120-129 is expanded and duplicates count once.
  3. Set New segments requested, Hosts per segment, Growth headroom, and the Per-segment IPv4 prefix. Add Infrastructure addresses per segment when gateways or other non-endpoint addresses must be held back.
  4. Choose an Allocation strategy. Lowest available sorts the whole lane numerically; normal first prefers IDs through 1001; extended first prefers IDs from 1006 upward.
  5. Resolve VLAN inputs need attention before using the plan. Unreadable entries and IDs outside 1 through 4094 stop the calculation rather than being silently ignored.
  6. Review the assigned count, shortfall, remaining IDs, subnet spare, and first proposed IDs. Reconcile any reserved overlap or outside-profile notice with the source ledger before approving the queue.

Interpreting Results:

The plan fits only when both checks pass: every requested segment receives an ID and the selected prefix has at least as many usable addresses as the planned host demand. A positive host spare does not compensate for an ID shortfall, and remaining VLAN IDs do not compensate for a negative host spare.

  • Remaining after request is runway inside the selected profile after reservations, existing assignments, and the proposed queue are accounted for.
  • Subnet fit is the usable host count minus endpoints, infrastructure addresses, and rounded-up growth.
  • Utilization at or above 75% produces a warning; at or above 90% it becomes critical. These are planning cues from this model, not IEEE or vendor limits.
  • An extended-range notice means the proposed queue crossed above 1005. Confirm platform and operating-policy support before using those IDs.

Technical Details:

VLAN capacity is set arithmetic over one inclusive range. Reservations are removed first; existing IDs consume capacity only when they are inside the selected profile and are not already reserved. The allocation strategy changes order, not the number of available IDs.

Formula Core:

The ID result and subnet result are calculated independently, then reported together.

A=|P\(R∪E)| M=H+I+⌈H×g100⌉ U=232−p−2
SymbolMeaningUnit
PAll IDs in the selected profileVLAN IDs
RReserved IDs inside that profileVLAN IDs
EExisting non-reserved IDs inside that profileVLAN IDs
AAvailable IDs before the new requestcount
H, I, gEndpoints, infrastructure addresses, and growth percentage per segmentcount, count, %
p, UIPv4 prefix length and usable addressesbits, hosts

Assigned count is the smaller of requested segments and available IDs. Shortfall is the requested count minus assigned count, never below zero. Remaining runway is available IDs minus assigned count. Pool utilization uses existing non-reserved IDs plus assigned IDs divided by the profile size after reservations; the display may round the percentage, but comparisons use the full value.

Rule Core:

ConditionResult
Requested segments > available IDsCritical ID shortfall; only the available count is assigned
U − M < 0Critical subnet shortfall; the largest prefix from /30 down to /1 that fits is suggested
Utilization ≥ 90%Critical runway cue
75% ≤ utilization < 90%Warning runway cue
Existing ID also reservedOverlap warning; it is excluded once, not counted as an active usable assignment

Input ranges are inclusive: VLAN IDs 1 to 4094, 0 to 100,000 new segments, 1 to 10,000,000 endpoint hosts, 0% to 1,000% growth, prefixes /1 to /30, and 0 to 1,000,000 infrastructure addresses. Invalid lists stop the result.

Planning Limitations:

The result models identifiers and ordinary IPv4 endpoint capacity. It does not inspect switches, discover active VLANs, test trunks, reserve DHCP addresses individually, or validate routing and security policy.

  • Platform-internal VLAN allocations and supported VLAN counts may be narrower than the selected profile.
  • The host formula excludes network and broadcast addresses but does not model point-to-point /31 subnets.
  • Growth is rounded up once per segment and applies to endpoint count only; infrastructure addresses are added afterward.

Worked Examples:

Enterprise lane with twelve new segments

Using IDs 2 through 4094, reserving 1002 through 1005 and 4094, and recording eight existing assignments leaves 4,080 IDs available before the request. Twelve proposed segments are assigned without a shortfall, leaving 4,068. For 180 endpoint hosts with 25% growth, the rounded growth allowance is 45 and planned demand is 225 hosts. A /24 supplies 254 usable addresses, so each segment has 29 addresses of spare capacity.

References: