Switches learn MAC addresses through a process called MAC address learning or MAC address table building. Here’s a simplified explanation of how it works:
- When a switch is first powered on or when it receives network traffic from a new device, it starts with an empty MAC address table.
- When a device sends an Ethernet frame to the switch, the switch examines the source MAC address of the frame.
- The switch checks its MAC address table to see if it already has an entry for that MAC address.
- If the MAC address is not found in the table, the switch adds an entry to the table. The entry includes the MAC address and the port on which the frame was received.
- The switch then forwards the frame to the appropriate port(s) based on the destination MAC address.
- If the switch receives another frame with the same source MAC address, it updates the port information in the MAC address table for that MAC address.
- The switch periodically checks the MAC address table for outdated entries. If a certain period of time elapses without any frames being received from a specific MAC address, the switch removes that entry from the table.
- This process continues as devices on the network communicate with each other, allowing the switch to dynamically learn and update MAC address information in its table.
By learning and maintaining MAC address information, switches can efficiently forward network traffic only to the appropriate ports, improving network performance and security.