Karthik Kadambi

MAC Addresses

How Local Devices Identify Each Other

An IP address identifies a device on a network logically. But before IP can work, devices need a way to identify each other physically on the local network. That role is handled by MAC addresses.

Every network device has a MAC address. It operates at a lower level than IP and plays a critical role in how data moves inside local networks like your home Wi-Fi or office LAN.

This article explains what a MAC address is, why it exists, and how it works with IP.

What is a MAC address

MAC stands for Media Access Control.

A MAC address is a unique identifier assigned to a network interface. It is usually hardcoded by the manufacturer into the network card.

Examples of network interfaces:

A MAC address looks like this:

00:1A:2B:3C:4D:5E

It is written in hexadecimal format and is 48 bits long.

Why MAC addresses exist

IP addresses can change. MAC addresses are meant to be stable.

MAC addresses exist to:

Without MAC addresses, devices on the same network would not know how to reach each other at the physical level.

MAC address vs IP address

This distinction is very important.

MAC address

IP address

You can think of it this way:

IP address answers where a device is

MAC address answers who the device is locally

Both are required for communication to succeed.

Structure of a MAC address

A MAC address has two parts.

Organizationally Unique Identifier (OUI)

The first 24 bits identify the manufacturer. Examples:

Apple

Intel

Samsung

Realtek

Device Identifier

The remaining 24 bits uniquely identify the device made by that manufacturer.

This structure helps ensure global uniqueness.

How MAC addresses are used in communication

When a device wants to send data to another device on the same local network it must know the destination MAC address.

The flow looks like this:

Switches use MAC addresses to forward frames efficiently.

MAC addresses and switches

Switches operate using MAC addresses.

A switch:

Forwards frames only to the correct port

This makes switches far more efficient than hubs, which broadcast everything.

What happens when the MAC address is unknown

If a device does not know the destination MAC address it cannot send the frame.

This is where ARP comes in.

The device asks: “Who has this IP address?”

The device with that IP replies with its MAC address.

This process is called Address Resolution Protocol and it is the bridge between IP and MAC.

MAC address scope and limitations

MAC addresses are valid only inside a local network.

Routers:

This means MAC addresses never cross routers. Only IP addresses travel across networks.

MAC address spoofing

MAC addresses can be changed in software. This is called MAC spoofing.

Reasons people spoof MAC addresses:

Because MAC addresses are not encrypted or authenticated they should not be used as a security mechanism.

MAC addresses and privacy

Modern devices use MAC randomization.

This prevents:

Your real MAC address is hidden when scanning for networks.

Common misconceptions

Misconception 1

MAC addresses are globally visible. No. They are visible only on the local network.

Misconception 2

MAC addresses are secret. No. They are sent in plain text on the network.

Misconception 3

MAC addresses provide security. They do not. They are identifiers, not security controls.

Conclusion

MAC addresses are the foundation of local network communication. They allow devices to identify each other and enable switches to forward traffic efficiently. While IP handles global routing, MAC addresses handle local delivery. Understanding MAC addresses makes ARP, switching and routing much easier to understand.

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