Intermediate level · Module 3: Switching and VLANs · Lesson 1 of 3
How Switches Work
Understand how switches learn and forward traffic.
In this lesson you will
- Explain MAC learning and forwarding
- Read a MAC address table
Key concepts
MAC addressMAC tablefloodingcollision and broadcast domains
The lesson
A switch learns which MAC address is on each port by reading the source of incoming frames, building a MAC address table.
It forwards frames only to the right port; unknown destinations and broadcasts are flooded to all ports in the same VLAN.
Each switch port is its own collision domain; the whole VLAN is one broadcast domain.
Step by step
- Clear and view the MAC table.
- Generate traffic.
- Observe the table filling.
- Explain flooding.
Practice activity
Observe and explain MAC learning in Packet Tracer.
Expected result: A correct explanation with MAC table evidence.
Check your understanding
-
How does a switch learn MAC addresses?
Show answer
From the source address of incoming frames.
-
What happens to a broadcast frame?
Show answer
It is flooded to all ports in the VLAN.
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