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Ethernet & Switching Basics

Technology Fundamentals

Ethernet & Switching Basics

2 min readPublished 22 Jul 2026

Ethernet is the dominant wired LAN technology. Understanding frames, MAC addresses and how switches forward them is the foundation of local networking.

Interactive explainer

How a Switch Learns & Forwards

Frames, MAC learning and the difference between forwarding and flooding.

SWITCHMAC tableP1 → AP2 → BHost AHost BHost C

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Ethernet frame

The unit of delivery.

Data travels across a LAN in Ethernet frames. Each frame carries a source and destination MAC address, the payload and a checksum (FCS) to detect corruption.

Check your understanding

1. What does a switch record to build its MAC table?

2. What does a switch do with an unknown destination MAC?

Keep learning

Ethernet & Switching BasicsSwitching & VLANs CompTIA Network+
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The core idea

  • Data travels in frames; each device has a unique 48-bit MAC address.
  • Switches build a MAC address table and forward frames only to the right port.
  • Modern Ethernet is full-duplex (send and receive at once) over Cat5e/Cat6 cabling.
Interactive explainer

How ARP Finds a MAC Address

Turning a known IP into the MAC address needed to deliver a frame.

11. Have IP, need MAC22. ARP request (broadcast)33. ARP reply (unicast)44. Cache the mapping

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1. Have IP, need MAC

Build the frame.

A device wants to send to an IP on its local network but only knows the IP. To build the Ethernet frame it also needs the destination's MAC address.

Check your understanding

1. How is an ARP request sent?

2. What does ARP resolve?

Keep learning

Ethernet & Switching BasicsIP Addressing & Subnetting CompTIA Network+
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How it works in practice

  • Speeds range from 100 Mbps to 1/10/40 Gbps depending on hardware and cable.
  • Auto-negotiation sets speed and duplex between devices.
  • A switch floods a frame only when the destination MAC is unknown.

Common mistakes

  • Confusing MAC addresses (Ethernet) with IP addresses (Layer 3).
  • Duplex mismatches causing slow, error-prone links.
  • Using the wrong cable category for the required speed.

Why it matters for your career

Ethernet and MAC-based switching are bedrock Network+ and CCNA knowledge that every networking role assumes you understand.

Technical interview questions

  1. What is a MAC address and how long is it?
  2. How does a switch decide where to forward a frame?
  3. What is a duplex mismatch?

Practice questions

  1. How many bits is a MAC address? (48)
  2. What table does a switch build? (MAC address table)
  3. What does a switch do with an unknown destination? (Floods the frame)

Where this fits in your networking journey

This is one concept in the Networking Fundamentals path, which leads into CompTIA Network+ and Cisco CCNA. When this clicks, review TCP/IP & Encapsulation and continue with IP Addressing & Subnetting.

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Interview Intelligence

How this topic actually shows up in interviews — and how to demonstrate you understand it.

Why employers ask about this

Switching is core LAN knowledge; interviewers check you understand MAC learning and forwarding.

Technical questions
How does a switch know where to send a frame?+

It learns source MAC addresses per port to build a MAC table, then forwards to the matching port (or floods if unknown).

What is a MAC address?+

A unique hardware address burned into a network interface, used for Layer 2 delivery.

Behavioural questions
Explain the difference between a switch and a hub.+

A switch forwards intelligently per port; a hub blindly repeats to all ports.

Real-world scenarios
“The network slows and broadcasts spike after a change.”+

Expected answer: Suspect a switching loop; verify Spanning Tree is working.

Common candidate mistakes
  • •Confusing MAC (L2) with IP (L3).
  • •Not knowing how switches learn.
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Employability Intelligence

Where this knowledge takes you — the jobs, skills and certifications it feeds into.

Relevant roles
Network SupportNetwork Administrator
Skills you're proving
EthernetSwitchingMAC addressingARP
Recommended certifications
CompTIA Network+
Career progression

Network Support → Network Administrator.

What employers expect

That you understand local delivery at Layer 2.

Frequently asked questions

What is ethernet & switching basics in networking?

Ethernet is the dominant wired LAN technology. Understanding frames, MAC addresses and how switches forward them is the foundation of local networking.

What is a MAC address and how long is it?

Data travels in frames; each device has a unique 48-bit MAC address. Switches build a MAC address table and forward frames only to the right port.

Do I need this for Network+ or CCNA?

Yes — Ethernet & Switching Basics is a core concept in CompTIA Network+ and Cisco CCNA. Understanding it here first makes the certification material much easier.

Related guides

Networking Fundamentals: The Complete Free Vendor-Neutral GuideTCP/IP & EncapsulationIP Addressing & SubnettingThe OSI Model Explained

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