How does a switch learn MAC Addresses?

If you have ever worked with computer networks, you may have heard of a switch. A switch is a networking device that connects devices together in a network. One of the primary functions of a switch is to forward data packets between devices in the network.

However, for the switch to know where to send the data packets, it needs to know the Media Access Control (MAC) addresses of the devices in the network. In this article, we will explore how a switch learns MAC addresses.

Understanding MAC addresses

Before we dive into how a switch learns MAC addresses, let us first understand what MAC addresses are. A MAC address is a unique identifier assigned to a network interface controller (NIC) for use as a network address in communications within a network segment.

A MAC address is a 48-bit address expressed in hexadecimal format, which means it consists of 12 hexadecimal digits. The first six digits represent the manufacturer’s unique identifier, while the last six digits represent the NIC’s unique identifier.

How does a switch learn MAC Addresses?

When a switch is first powered on, it does not know any MAC addresses in the network. The switch needs to learn the MAC addresses by examining the source MAC address of incoming data packets. There are two main ways that a switch can learn MAC addresses:

#1. Flooding

If the switch doesn’t have a MAC address in its table, it floods the packet out of all ports except the one it was received on. This mechanism ensures that the data packet reaches its intended destination, even if the switch doesn’t know the destination MAC address.

#2. MAC address table

As data packets are sent through the switch, the switch will start building a MAC address table. The table maps MAC addresses to the physical ports on the switch.

When a switch receives a data packet, it examines the source MAC address and updates its MAC address table with the MAC address and the port it received the packet.

The switch then forwards the data packet to the appropriate port based on the destination MAC address in its MAC address table.

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Types of MAC address learning

There are two main types of MAC address learning:

1. Static MAC addresses learning

Static MAC address learning involves manually configuring the MAC addresses in the switch’s MAC address table. This approach is commonly used for devices that are always connected to the network, such as servers or printers.

2. Dynamic MAC addresses learning

Dynamic MAC address learning involves the switch automatically learning MAC addresses as devices connect to the network. This approach is commonly used for devices that are frequently added or removed from the network, such as laptops or mobile devices.

MAC address aging

MAC addresses are not permanent, and devices can change their MAC addresses over time. To ensure that the MAC address table is up to date, switches use a process called MAC address aging.

MAC address aging involves removing MAC addresses from the table after a certain period of time has elapsed since the switch last received a data packet from the device. By default, most switches use a MAC address aging time of five minutes.


Switches play a critical role in modern computer networks, and the ability to learn MAC addresses is one of the primary reasons why switches are so important.

By using a combination of flooding and MAC address table building, switches can quickly and efficiently forward data packets to their intended destinations. Understanding how switches learn MAC addresses is an essential part of network engineering.

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