VLAN Calculator

Plan subnets, look up VLAN IDs, decode 802.1Q frames and build trunk configurations. 100% browser-based.

100% local VLAN 1–4094 802.1Q Reference Import / Export JSON

VLAN Subnet Planner

Base Network (CIDR) Enter a valid IPv4 CIDR block

Split Mode

Number of VLANs

Starting VLAN ID VLAN IDs assigned sequentially

Enter a base network and click Calculate to plan your VLANs.

VLAN ID Quick Lookup

VLAN ID (1–4094)

Type a VLAN ID to see its classification and usage information.

VLAN ID Range Reference

VLAN 1

Default VLAN

Factory default. All ports are in VLAN 1 by default. Cannot be deleted or renamed on most platforms.

VLAN 2 – 1001

Normal Range

Standard user VLANs. Supported in all VTP modes. Stored in the VLAN database (vlan.dat). Best choice for production networks.

VLAN 1002 – 1005

Reserved (FDDI / Token Ring)

Reserved for FDDI and Token Ring. Cannot be deleted. Avoid using these in modern Ethernet networks.

VLAN 1006 – 4094

Extended Range

Extended VLANs. Requires VTP transparent or VTP off mode. Not stored in vlan.dat. Available in Cisco IOS 12.2(25)EW+ and similar platforms.

Range	Name	Count	VTP Support	Notes
1	Default	1	All modes	Reserved by system; cannot delete
2 – 1001	Normal	1,000	All modes	Stored in vlan.dat; fully managed via VTP
1002 – 1005	Reserved	4	All modes	FDDI/Token Ring legacy; cannot delete
1006 – 4094	Extended	3,089	Transparent / Off only	Not in vlan.dat; stored in running-config

802.1Q Frame Structure

Destination MAC

6 bytes

48 bits

Source MAC

6 bytes

48 bits

TPID

2 bytes

0x8100

TCI
2 bytes
16 bits

                PCP 3b
                DEI 1b
                VID 12b
              

EtherType

2 bytes

e.g. 0x0800

Payload

46–1500 bytes

MTU 1518 → 1522

FCS

4 bytes

CRC-32

802.1Q Overhead

The 802.1Q tag inserts 4 bytes (TPID 2B + TCI 2B) between the Source MAC and EtherType fields. This increases the standard Ethernet maximum frame size from 1518 bytes to 1522 bytes. Switches must support "baby giants" or have a larger MTU configured.

TCI Bit Calculator

PCP (0–7)

DEI (0 or 1)

VID / VLAN ID (1–4094)

PCP — Priority Code Point (IEEE 802.1p)

PCP	Priority	Name	Typical Use	Level

QoS Note

PCP values are used for QoS (Quality of Service) marking at Layer 2. PCP 7 is the highest priority (network control), PCP 0 is Best Effort. Values are mapped to DSCP at Layer 3 boundaries for end-to-end QoS.

Router-on-a-Stick

A single physical router interface is divided into multiple sub-interfaces, each carrying traffic for one VLAN. The switch port connecting to the router must be configured as a trunk. Cost-effective for small networks.

Limitation

All inter-VLAN traffic flows through one physical link — creates a bottleneck. Suitable for low-traffic environments only.

Cisco IOS Example — Sub-interfaces

interface GigabitEthernet0/0
 no shutdown

interface GigabitEthernet0/0.10
 encapsulation dot1Q 10
 ip address 10.0.10.1 255.255.255.0
 description VLAN 10 - Management

interface GigabitEthernet0/0.20
 encapsulation dot1Q 20
 ip address 10.0.20.1 255.255.255.0
 description VLAN 20 - Production

interface GigabitEthernet0/0.30
 encapsulation dot1Q 30
 ip address 10.0.30.1 255.255.255.0
 description VLAN 30 - DMZ

Layer 3 Switch (SVI)

A Layer 3 switch performs routing internally using Switched Virtual Interfaces (SVI). Each VLAN has a virtual interface acting as the default gateway. This provides wire-speed routing without external routers.

Advantage

Routing happens at hardware speed in the switch ASIC. Ideal for large campus networks. No bandwidth bottleneck between VLANs.

Cisco IOS Example — SVI

ip routing

vlan 10
 name Management
vlan 20
 name Production
vlan 30
 name DMZ

interface Vlan10
 ip address 10.0.10.1 255.255.255.0
 no shutdown

interface Vlan20
 ip address 10.0.20.1 255.255.255.0
 no shutdown

interface Vlan30
 ip address 10.0.30.1 255.255.255.0
 no shutdown

Comparison: Router-on-a-Stick vs L3 Switch

Criteria	Router-on-a-Stick	L3 Switch (SVI)
Cost	Low — uses existing router	Higher — requires L3 capable switch
Performance	Limited by physical link speed	Wire-speed, hardware-based routing
Scalability	Limited (bottleneck)	Excellent
Best for	Small offices, labs, <5 VLANs	Enterprise, campus, data centre
Config complexity	Low	Medium (need ip routing command)

Trunk Configuration Builder

Interface

Native VLAN Untagged traffic on trunk. Best practice: use a dedicated native VLAN (not VLAN 1).

Allowed VLANs Comma-separated VLAN IDs or ranges (e.g. 10-20,30)

Encapsulation

Platform

Generated Configuration

! Click "Generate Config" to build your trunk configuration

Native VLAN — Best Practices

Security Warning

Never use VLAN 1 as the native VLAN in production. VLAN 1 is the default and is often targeted by VLAN hopping attacks. Use a dedicated unused VLAN (e.g. VLAN 99) as the native VLAN and ensure it carries no user traffic.

Consistency Required

The native VLAN must match on both ends of a trunk link. A mismatch causes a CDP/STP native VLAN mismatch warning and can lead to traffic being forwarded to the wrong VLAN.

VTP (VLAN Trunking Protocol) Modes

Mode	Syncs from server	Advertises	Extended VLANs	Use case
Server	Yes	Yes	No	Authoritative VTP server, manages VLAN database
Client	Yes	Yes	No	Receives VLAN updates, cannot create/delete VLANs
Transparent	No	Forwards only	Yes	Independent VLAN database, passes VTP but ignores it
Off	No	No	Yes	No VTP participation — recommended for security