🔁 Switching Fundamentals

MAC address tables, MAC filtering, and VLANs explain how switches think, learn, secure, and segment networks. These are core CCST concepts and are heavily used in Cisco Packet Tracer labs and real networks built using Cisco Systems devices.

🧠 PART 1: MAC Address Tables

📌 What Is a MAC Address Table?

A MAC address table (also called a CAM table) is a memory table inside a switch that maps:

    MAC Address  →  Switch Port

Purpose: Helps the switch forward frames only to the correct port.

🔁 How a Switch Learns MAC Addresses

🧪 Example Network

    PC1 ──(Fa0/1) Switch (Fa0/2)── PC2

PC1 sends a frame
Switch reads the source MAC
Stores it in MAC table
If destination MAC is known → forward
If unknown → flood to all ports (except incoming)

📊 Sample MAC Address Table

MAC Address	Port
AA:BB:CC:11	Fa0/1
DD:EE:FF:22	Fa0/2

Switches learn source MAC, not destination MAC.

❌ What If MAC Table Is Empty?

First frame is flooded
Reply populates MAC table
Network becomes efficient

🧠 Real-World Benefits

Faster communication
Less network traffic
Improved security

🔐 PART 2: MAC Filtering (MAC-Based Security)

📌 What Is MAC Filtering?

MAC filtering allows or blocks devices based on their MAC address.

“Only approved devices are allowed on the network.”

🔧 How MAC Filtering Works

Admin defines allowed MAC addresses
Switch checks device MAC
Allows or blocks access

🧪 Example (Office Security)

    Allowed:
    AA:BB:CC:11 (PC)
    DD:EE:FF:22 (Printer)
    
    Unknown laptop → Blocked

✅ Advantages

Prevents unauthorized access
Easy to configure

❌ Limitations (Exam Important)

MAC spoofing possible
Not scalable for large networks

MAC filtering = Basic security, not foolproof

🧠 Where MAC Filtering Is Used

Switch port security
Home Wi-Fi routers
Small office networks

🧩 PART 3: VLAN Concepts

📌 What Is a VLAN?

A VLAN (Virtual LAN) is a logical network created inside a switch.

Devices can be separated even if they are on the same physical switch.

🧠 Why VLANs Are Needed

Without VLAN	With VLAN
One big broadcast domain	Separate networks
More traffic	Less broadcast traffic
Low security	Better security

🧪 Example (Same Switch, Different VLANs)

    Switch
    ├── VLAN 10 → HR PCs
    ├── VLAN 20 → IT PCs

HR and IT are isolated
No direct communication

VLAN = Separate broadcast domains

🧠 Key Rule

VLANs cannot communicate without a Layer 3 device.

🔀 Inter-VLAN Communication

Router-on-a-stick
Layer 3 switch

📊 VLAN Benefits (Exam-Ready)

Benefit	Explanation
Security	Departments isolated
Performance	Reduced broadcast traffic
Flexibility	Logical grouping
Scalability	Easy expansion

🧠 VLAN IDs (Quick Facts)

VLAN 1 = Default VLAN
VLAN range: 1–4094
Each VLAN = separate broadcast domain

🔍 MAC Table + VLAN (IMPORTANT)

Switch maintains separate MAC tables per VLAN.

    VLAN 10: MAC A → Fa0/1
    VLAN 20: MAC A → Fa0/3

Same MAC address in different VLANs is allowed.

📊 Switching Fundamentals – Combined Summary

Concept	Purpose
MAC Address Table	Efficient forwarding
MAC Filtering	Device-level security
VLAN	Network segmentation