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Layer 2 Device Overview

Feb. 24, 2021
1m 17s

An quick fundamental overview of layer two devices.


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A layer 2 device is a device that makes a forwarding decision on a physical address. Most commonly, you’ll find a bridge or a switch and the address they use is a MAC address. When a frame arrives at the device, it first takes the source address and places it in the MAC address table for 300 seconds (or five minutes).

Then It will look up the destination address.

If the destination address can be found, it will be forwarded out of that port explicitly.

If the destination address cannot be found, it will forward it out all ports of the same VLAN to which the receiving interface belonged.

This is called flooding. Your MAC address table has three important pieces of information:

  1. Interface in which the frame was received
  2. The source MAC address of the frame, and
  3. The VLAN to which the interface belonged.


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