What is a MAC address?

A MAC address (Media Access Control address) is a unique hardware address of a network device, used at the data link layer (L2) to deliver data within a local network.

Put simply: A MAC address is the "physical address" of a network card, by which devices find each other on the same network.

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#Why a MAC address is needed

A MAC address is needed to:

• understand who the frame is intended for
• deliver data from one device to another within a LAN
• let the switch know which port to send the frame to

Without MAC addresses the data link layer could not deliver data by address.

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#What a MAC address looks like

A MAC address is usually:

• length: 48 bits (6 bytes)
• written in hexadecimal form

Example:

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

or

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

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#What a MAC address consists of

A MAC address is logically split into two parts:

#1. The first 3 bytes: the OUI

• the manufacturer identifier
• shows which company made the device

#2. The last 3 bytes: a unique number

• assigned by the manufacturer
• unique within that OUI

As a result, a MAC address is unique worldwide (under normal circumstances).

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#Where a MAC address is used

A MAC address:

• is used in Ethernet and Wi-Fi frames
• works only within a single local network
• is not passed through routers (each segment gets a new frame)

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#Important points for an interview

• A MAC address:
  • belongs to the data link layer
  • does not replace an IP address
• MAC:
  • is used for delivering frames
  • IP is for routing between networks

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#Can a MAC address be changed?

Yes.

• in software (MAC spoofing)
• often used for testing, privacy, or bypassing restrictions

But:

• the factory MAC address is still "burned into" the device

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#Simple analogy

A house in a residential complex:

• the MAC address is the apartment number
• the IP address is the city's postal address

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#Short version for an interview

A MAC address is a unique hardware address of a network interface, used at the data link layer to deliver frames between devices on a single local network.