MAC Address & Ethernet

When devices communicate on a local network, such as your home Wi-Fi or office LAN, they need a way to identify each other. This is where MAC addresses come in.

At the same time, devices need a set of rules and technologies for sending data across the local network. This is where Ethernet comes in.

So, in simple terms:

MAC Address identifies a network interface, while Ethernet is a technology used to communicate over a local network.

Let's understand both separately.

What Is a MAC Address?

MAC stands for Media Access Control.

A MAC address is a link-layer address used to identify a network interface on a local network.

It is commonly represented as a 48-bit value written in hexadecimal.

For example:

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

You may also see it written as:

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

A typical Ethernet MAC address contains 6 bytes (48 bits).

Structure of a MAC Address

A MAC address is made up of six hexadecimal pairs:

00 : 1A : 2B : 3C : 4D : 5E
│             │
First 3       Last 3
bytes         bytes

The first part traditionally identifies the organization that was assigned the address block, while the remaining part identifies the interface within that block.

However, not every MAC address follows the traditional globally assigned pattern. Some addresses are locally administered or used for special purposes.

MAC Address vs IP Address

Students often confuse MAC addresses with IP addresses.

They serve different purposes.

Think of it like this:

MAC Address → Local network identity

IP Address → Logical address used for network communication and routing

What Is Ethernet?

Ethernet is a family of networking technologies used to connect devices over local networks.

It defines how devices communicate over Ethernet links, including things such as:

• Frame format

• MAC addressing

• Physical signaling

• Data transmission

• Link operation

Ethernet is standardized as part of the IEEE 802.3 family of standards.

It is widely used in:

• Home networks

• Offices

• Schools

• Data centers

• Enterprise networks

How Does Ethernet Work?

Suppose your computer wants to send data to another computer on the same Ethernet network.

The data is placed inside an Ethernet frame.

A simplified Ethernet frame contains information such as:

┌────────────┬────────────┬───────────┐
│ Destination│   Source   │   Data    │
│ MAC Address│ MAC Address│           │
└────────────┴────────────┴───────────┘

The destination MAC address tells the local network which interface should receive the frame.

The source MAC address identifies the interface that sent it.

Ethernet frames also contain additional fields, such as a type/length field and an error-detection field.

Ethernet and Switches

Ethernet is commonly used with network switches.

Imagine four computers connected to a switch:

PC 1 ──┐
PC 2 ──┤
PC 3 ──┼── Switch
PC 4 ──┤
Printer┘

The switch learns which MAC addresses are reachable through its ports.

When a frame arrives, the switch can use its MAC address table to decide where to forward the frame.

For example:

Destination MAC
      ↓
MAC Address Table
      ↓
Correct Switch Port
      ↓
Destination Device

This is much more efficient than simply sending every frame to every device.

MAC Address Example

Suppose a computer has this MAC address:

A4:5E:60:12:34:56

If it sends an Ethernet frame to another computer with MAC address:

B8:27:EB:98:76:54

the frame can contain:

Source MAC:
A4:5E:60:12:34:56

Destination MAC:
B8:27:EB:98:76:54

The Ethernet network uses these addresses for delivery across the local link.

Ethernet vs Wi-Fi

Ethernet and Wi-Fi are both commonly used for local networking, but they use different physical and link technologies.

So, when you connect your laptop to a router using an Ethernet cable, you're using Ethernet. When you connect using Wi-Fi, you're using Wi-Fi.

MAC Address in Wi-Fi

MAC addresses are not limited to Ethernet.

Wi-Fi also operates at the link layer and uses MAC addressing.

For example:

Laptop ── Wi-Fi ── Access Point

The laptop and access point use link-layer addressing to communicate over the wireless network.

So remember:

MAC addressing is a link-layer concept used by technologies such as Ethernet and Wi-Fi.

Can a MAC Address Change?

Yes. Although MAC addresses are commonly associated with network hardware, the address used by an interface can sometimes be changed or randomized by software.

Modern operating systems may use MAC address randomization when connecting to Wi-Fi networks to improve privacy.

Therefore, it is better to think of a MAC address as the link-layer address currently being used by a network interface, rather than assuming it is always permanently fixed.

Why Are MAC Addresses Important?

MAC addresses are important for local network communication because they allow network technologies such as Ethernet and Wi-Fi to identify network interfaces.

They are especially important for:

• Local network communication

• Ethernet frames

• Network switches

• Wi-Fi communication

• Network troubleshooting

Conclusion

A MAC address is a link-layer address used to identify a network interface on a local network, while Ethernet is a widely used family of wired networking technologies.

The easiest way to remember the difference is:

MAC Address → Identifies the interface at the local-link level

Ethernet → Provides the technology and rules for wired local-network communication

When combined with switches, IP addresses, and routers, these technologies form an important part of how modern computer networks work.