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How does Ethernet work?

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Quick answer

Ethernet is a wired networking technology that sends data in frames over cables. Each frame includes the MAC address of the intended recipient. All devices on the same network segment receive the frame, but only the device with the matching MAC address accepts it. Switches improve efficiency by forwarding frames only to the correct port.

Ethernet sends data over a wired network by breaking it into frames that carry source and destination MAC addresses. Each device on the same local network receives every frame, but only the one whose MAC address matches the destination accepts it.

Step by step

  1. A device prepares data to send and encapsulates it into an Ethernet frame with source and destination MAC addresses.
  2. The frame is transmitted as electrical signals over the Ethernet cable connected to the device's network interface card.
  3. The signals travel through the cable to a switch or hub, which receives the frame on one of its ports.
  4. A switch reads the destination MAC address and looks it up in its MAC address table to determine which port to forward the frame to.
  5. The switch sends the frame out only the correct port, where the destination device receives it and checks the MAC address.
  6. If the MAC address matches, the device accepts the frame and passes the payload up to higher network layers; otherwise it discards the frame.

Key things to understand

  1. Ethernet is a family of wired networking standards that define how devices format and transmit data over cables.
  2. Data is divided into frames, each containing a header with source and destination MAC addresses, the payload, and a trailer with error-checking bits.
  3. When a device sends a frame, it travels through the cable to every device on the same local network segment.
  4. Each receiving device compares the frame's destination MAC address to its own; if they match, it accepts the frame, otherwise it discards it.
  5. Modern switched Ethernet uses a switch to learn which MAC addresses are on which ports and forwards frames only to the correct port, reducing unnecessary traffic.

Labelled diagram

  1. Sender

    Device creates a frame with its own MAC as source and the recipient's MAC as destination.

  2. Cable

    Electrical signals representing the frame travel through twisted-pair or fiber-optic cables.

  3. Switch

    Switch reads the destination MAC and looks up which port leads to that address.

  4. Forwarding

    Switch sends the frame out only the correct port, not to all devices.

  5. Receiver

    Destination device verifies the MAC address matches and accepts the frame.

How an Ethernet frame travels from sender to receiver

Real-world examples

  • In a home office, a desktop computer connects to a router via an Ethernet cable to get a stable internet connection for video calls.
  • In a large office building, hundreds of computers are linked to Ethernet switches that form a local area network for sharing files and printers.
  • Data centers use Ethernet to connect thousands of servers, often with fiber-optic cables for high-speed communication between machines.
  • A gaming console plugged into a router with an Ethernet cable often experiences lower latency than a Wi-Fi connection, reducing lag during online play.

Common mistake

✗ Myth: Ethernet always sends data to every device on the network, causing collisions and slowing everyone down.

✓ Fact: While early Ethernet used hubs that broadcast to all devices, modern Ethernet uses switches that learn MAC addresses and forward frames only to the intended recipient. This eliminates unnecessary traffic and collisions, making networks faster and more efficient.

People also ask

What is ethernet and how does it work?
Ethernet is a wired networking standard that defines how devices format and transmit data over cables. It breaks data into frames, each with source and destination MAC addresses. These frames travel through cables to a switch, which forwards them only to the device with the matching MAC address, enabling reliable communication within a local network.
How fast is ethernet?
Ethernet speeds range from 10 Mbps in older standards to 100 Gbps and beyond in modern data centers. Common home and office speeds are 1 Gbps (1000BASE-T) and 10 Gbps. The actual speed depends on the cable category, network hardware, and the capabilities of connected devices.
Can i use ethernet without internet?
Yes, Ethernet can be used to connect devices on a local network without internet access. For example, you can link two computers directly with an Ethernet cable to transfer files, or connect to a local server or printer. Internet access requires an additional connection to an internet service provider.
What is a MAC address?
A MAC address is a unique 48-bit identifier burned into every Ethernet network interface card by its manufacturer. It is written as six pairs of hexadecimal digits, like 00:1A:2B:3C:4D:5E. Devices on the same local network use MAC addresses to direct frames to the correct recipient.
How does Ethernet differ from Wi-Fi?
Ethernet uses physical cables to carry signals, while Wi-Fi uses radio waves through the air. Ethernet typically offers more stable and faster connections with lower latency because the signal is not subject to interference or sharing the airwaves with other devices.
What is an Ethernet frame?
An Ethernet frame is the basic unit of data transmission, containing a header with destination and source MAC addresses, a payload of up to 1500 bytes, and a trailer with a frame check sequence for error detection. Frames are the envelopes that carry your data across the local network.
Why do some Ethernet cables have different categories like Cat5e or Cat6?
Categories indicate the cable's construction and performance. Cat5e supports speeds up to 1 Gbps, while Cat6 can handle 10 Gbps over shorter distances. Higher categories have tighter twists and better shielding to reduce interference and support faster data rates.

Part of the guide: How the Internet Works →