VLAN Interface Calculator
Calculate available VLAN IDs and subinterface count for 802.1Q tagged networking.
About VLAN Interface Calculator
IEEE 802.1Q VLAN tagging inserts a 4-byte tag (2 bytes TPID + 2 bytes TCI, carrying the VLAN ID and priority bits) into each Ethernet frame, which adds a small but nonzero bandwidth cost proportional to frame rate — negligible for large frames but more noticeable for small, high-rate traffic. The 12-bit VLAN ID field theoretically allows 4096 values, but 0 (untagged/priority-only) and 4095 (reserved) are excluded, leaving a maximum of 4094 usable VLAN IDs per bridge domain — a hard ceiling relevant to large multi-tenant or service-provider deployments.
Formula
VLAN tagging overhead
tagged_frame_size = untagged_size + 4 bytes; max VLAN IDs = 4094
- L_{untagged}
- original frame size in bytes
Worked example
With the default values below, VLAN Interface Calculator returns VLAN IDs Remaining (of 4094 max) of 4,082. Change any input above and every figure here is recalculated in your browser.
Inputs used
- VLANs Needed on This Interfaceminimum 0
- 12
- Untagged Frame Size (bytes)accepts 46–9,000
- 1,500
- Frames per Secondminimum 0
- 50,000
Results
- VLAN IDs Remaining (of 4094 max)
- 4,082
- 802.1Q Tagging Overhead (Mbps)
- 1.6000
- Tagged Frame Size (bytes)
- 1,504
- Overhead as % of Frame
- 0.267%
- Within VLAN ID Capacity?
- true
Step by step
- 1Values used
- 2VLAN tagging overhead
- 3VLAN IDs Remaining (of 4094 max)= 4,082
- 4802.1Q Tagging Overhead (Mbps)= 1.6000
- 5Tagged Frame Size (bytes)= 1,504
- 6Overhead as % of Frame= 0.267
- 7Within VLAN ID Capacity?= Yes
Assumptions and limits
- The result is derived only from the 3 inputs listed above. Anything not among them is not part of the calculation.
- In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
- Figures are rounded for display to 4 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.
How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.
Frequently Asked Questions
How do I create and check VLAN interfaces on Linux?
`ip link add link eth0 name eth0.100 type vlan id 100` creates a VLAN subinterface for VLAN ID 100 on eth0; `ip -d link show eth0.100` confirms the VLAN ID and parent link. The `8021q` kernel module must be loaded (`modprobe 8021q`).
Why is the maximum VLAN ID 4094 and not 4096?
The 12-bit VLAN ID field spans 0-4095, but VLAN ID 0 is reserved to mean 'no VLAN, priority tag only' and VLAN ID 4095 is reserved by the 802.1Q standard for implementation use — leaving 1-4094 as the usable range for actual VLAN identifiers.
Does VLAN tagging overhead ever cause frames to exceed the MTU?
Yes — adding the 4-byte tag to an already-maximum-size 1500-byte payload frame can push it to 1504 bytes, which is why 802.1Q-aware switches and NICs typically support 'baby giant' frames (1500 + a few bytes) to accommodate tagged traffic without fragmentation.