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How Switches Forward Ethernet Frames? Explained

ethernet frames

A network cannot communicate without frames as they provide a well-structured format for transmitting data across a network. An encapsulation process creates a ‘frame’ when data is prepared to be sent over a network.

This process gives rise to a frame. Frames play an important role in Layer 2, i.e., the Data Link Layer in the Open Systems Interconnection (OSI) model. This model defines how the different network protocols interact.

The efficient transfer of data through a physical network link, like an Ethernet connection, is the responsibility of the data link layer. Before transmitting them over the network, it creates frames out of the data packets from Layer 3 of the network.

Note: If you have been following up with our new CCNA series, you might have come across the concept of configuration management tools. If you haven’t, I recommend you do so before jumping on to this blog.

In this blog, you will learn about the components of an Ethernet frame and how switches receive and forward these Ethernet frames.

What is meant by Ethernet frames?

The basic building blocks of data transfer in Ethernet networks are Ethernet frames. They are made up of a header and a payload that contain the transferred data. The frame length, source and destination MAC addresses, and error-checking information are all included in the header.

The structure of Ethernet frames is clearly defined. The following are the components of an Ethernet frame. These include a preamble, start frame delimiter, destination MAC address, source MAC address, EtherType or Length field, payload, and frame check sequence. You can learn in detail about them here.

The MAC addresses identify the source and destination devices, while the preamble and start frame delimiter connect the receiver with the incoming frame.

How are Ethernet Frames received by the switches?

The following steps are followed for the switch to receive Ethernet frames. These are:

  • Switch operation:

Switches are essential components of contemporary network architecture. A switch determines the correct port for forwarding when an Ethernet frame arrives by looking at the destination MAC address. A forwarding table, often referred to as a MAC address table, is kept up by the switch and is used to associate MAC addresses with certain switch ports.

  • MAC address learning:

Switches use MAC address learning to fill the forwarding tables on their devices. The source MAC address of each frame that a switch receives is extracted and connected to the port on which it originated. Through effective forwarding, the switch creates a database of MAC addresses and the relevant ports.

  • Filtering and forwarding:

A switch can decide how to forward frames once it has discovered a device’s MAC address. A switch only passes a frame to the correct port if the destination MAC address matches an item in its forwarding table when it receives the frame. By removing superfluous traffic, this method increases network effectiveness.

  • Broadcast and multicast handling:

When compared to unicast frames, switches treat broadcast and multicast frames differently. The switch forwards incoming broadcast frames to all associated ports, ensuring that they are received by all network nodes. Similarly to this, ports that have joined the multicast group are only forwarded multicast frames.

How are Ethernet Frames forwarded by the switch?

The following methodologies are followed by a switch to forward the Ethernet frames. These are mentioned below:

  • Unicast forwarding:

When a switch operates in unicast forwarding, it consults its forwarding table to identify the proper port for the destination when it receives an Ethernet frame with a specific MAC address as the target. So that the source and destination devices can communicate directly with one another, the switch then passes the frame directly to that port.

  • Broadcast and multicast forwarding:

A switch copies a broadcast or multicast frame and forwards it to all ports except the incoming port when it receives the message. By ensuring that every device on the network receives the frame, broadcast and multicast communication are effectively enabled.

What is the role of VLANs in Ethernet Frames?

The role of VLANs in Ethernet Frames is discussed below:

  • Basics of VLAN:

An approach to logically divide a physical network into several virtual networks is through the use of virtual local area networks (VLANs). By isolating traffic inside particular groups or departments, VLANs improve security, management, and scalability.

  • VLAN tagging:

Ethernet frames can be marked with VLAN tagging to show which VLAN they belong to. The switch adds a VLAN tag to an Ethernet frame when it enters a switch port that has been set up for VLANs. Switches can properly handle and forward frames with VLAN tags because of this tag, which contains information about the VLAN to which the frame belongs.

  • VLAN trunking:

Multiple VLANs can be carried over a single physical link between switches thanks to VLAN trunking. Trunk ports use unique trunking protocols like IEEE 802.1Q to transmit and receive packets from various VLANs. Network administration is made easier and resource management is made possible via tunneling.

It’s a wrap!

Data frames are an important component for receiving as well as sending data in a network, that too, reliably. We have discussed Ethernet frames in this blog and all the techniques involved in receiving and forwarding Ethernet frames through switches.

The fundamental units of communication in Ethernet networks are Ethernet frames. In order to ensure effective data transfer within local networks, switches are essential for accepting and forwarding these frames. Network administrators and anybody interested in computer networking should understand the design and functionality of Ethernet frames and switches.