Understanding VLANs and Their Operation¶

A VLAN (Virtual LAN) is an overlay layer 2 network that helps us organize devices into different groups connected to a virtual network on the physical network.

VLANs help us partition a LAN into smaller virtual networks for security purposes. This allows us to have different logically distinct virtual networks rather than having many physical small LANs.

Computers on the same network (LAN) communicate either through wireless access points (AP) or through ethernet cables. All computers on a LAN are connected to the same network switch.

Types of VLANs¶

There are two types of VLANs:

Port-Based VLAN: A VLAN is assigned to a particular port, and any machine connected to that port automatically joins that VLAN
User-Based or Dynamic VLAN: VLANs are assigned based on user authentication or other dynamic criteria

Network Architecture¶

flowchart TD
    subgraph "Physical Network Infrastructure"
        SW["Switch"]
    end

    subgraph "VLAN 10 (Marketing)"
        PC1["Computer 1\nIP: 192.168.10.2\nVLAN 10"]
        PC2["Computer 2\nIP: 192.168.10.3\nVLAN 10"]
    end

    subgraph "VLAN 20 (Engineering)"
        PC3["Computer 3\nIP: 192.168.20.2\nVLAN 20"]
        PC4["Computer 4\nIP: 192.168.20.3\nVLAN 20"]
    end

    subgraph "VLAN 30 (Finance)"
        PC5["Computer 5\nIP: 192.168.30.2\nVLAN 30"]
        PC6["Computer 6\nIP: 192.168.30.3\nVLAN 30"]
    end

    SW --- PC1
    SW --- PC2
    SW --- PC3
    SW --- PC4
    SW --- PC5
    SW --- PC6

    RT["Router\n(Inter-VLAN Routing)"]
    SW --- RT

    PC1 <--> PC2
    PC3 <--> PC4
    PC5 <--> PC6

    PC1 <-.-> |"Traffic Isolated\nUnless Routed"| PC3
    PC3 <-.-> |"Traffic Isolated\nUnless Routed"| PC5
    PC5 <-.-> |"Traffic Isolated\nUnless Routed"| PC1

    classDef vlan10 fill:#ffcccc,stroke:#ff0000
    classDef vlan20 fill:#ccffcc,stroke:#00ff00
    classDef vlan30 fill:#ccccff,stroke:#0000ff
    classDef network fill:#f9f9f9,stroke:#666666
    classDef router fill:#ffffcc,stroke:#ffcc00

    class PC1,PC2 vlan10
    class PC3,PC4 vlan20
    class PC5,PC6 vlan30
    class SW network
    class RT router