What is the format of a MAC address?

MAC addresses are 48 bits (6 bytes) in length and are typically represented in hexadecimal format with each byte separated by a colon or a hyphen. For example: 00:1A:2B:3C:4D:5E or 00-1A-2B-3C-4D-5E. Each byte is represented by two hexadecimal digits.

What is an OUI in a MAC address?

OUI stands for Organizationally Unique Identifier. It's the first 24 bits (3 bytes) of a MAC address that identifies the manufacturer or vendor of the network interface controller (NIC). The IEEE Registration Authority assigns OUIs to ensure uniqueness. For example, in the MAC address 00:1A:2B:3C:4D:5E, the OUI is 00:1A:2B.

Can MAC addresses be changed?

Yes, MAC addresses can be changed or 'spoofed' on most modern hardware through software. This is called MAC spoofing and is used for various purposes including network troubleshooting, privacy enhancement, or bypassing access controls. However, the original hardware MAC address is permanently assigned by the manufacturer.

What's the difference between a MAC address and an IP address?

MAC addresses operate at the data link layer (Layer 2) of the OSI model and identify physical devices on a local network segment. They don't change when moving between networks. IP addresses operate at the network layer (Layer 3) and can change depending on the network a device is connected to. MAC addresses are for local network communication, while IP addresses are for routing across different networks.

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What is a MAC Address?

Q: What is a MAC address?

A Media Access Control (MAC) address is a unique 48-bit identifier assigned to network interfaces for communications on a physical network. It's a hardware identification number that uniquely identifies each device on a network and is used for network communication between devices within a network segment.

A Media Access Control (MAC) address is a unique identifier assigned to network interfaces for communications on a physical network segment. It's often referred to as the physical address or hardware address because it's permanently assigned to a network device by the manufacturer.

MAC Address Definition and Purpose

MAC addresses are used in the Media Access Control protocol, a sublayer of the Data Link Layer (Layer 2) in the seven-layer OSI network model. Each network-enabled device contains a Network Interface Card (NIC) with a unique MAC address burned into its ROM, which is assigned by the manufacturer.

The primary purposes of MAC addresses are:

To uniquely identify devices within a network segment
To facilitate frame delivery on local networks
To control network access
To serve as the foundation for network bridging and switching

MAC Address vs. IP Address

While both MAC and IP addresses are used to identify devices on a network, they serve different purposes:

MAC Address	IP Address
Hardware-based, assigned by manufacturer	Software-based, assigned by network
Operates at Layer 2 (Data Link)	Operates at Layer 3 (Network)
48 bits (6 bytes) in length	32 bits (IPv4) or 128 bits (IPv6)
Local significance (within network segment)	Global significance (across internet)
Generally permanent (but can be spoofed)	Can change (dynamic) or be static

MAC Address Format

A MAC address consists of 48 bits (6 bytes) and is typically represented in hexadecimal format. There are several common notation methods:

Colon-hexadecimal: 00:1A:2B:3C:4D:5E
Hyphen-hexadecimal: 00-1A-2B-3C-4D-5E
Dot-hexadecimal: 001A.2B3C.4D5E (Cisco format)
Raw-hexadecimal: 001A2B3C4D5E

Each byte (2 hexadecimal digits) can represent values from 00 to FF (0 to 255 in decimal).

MAC Address Structure and OUI

A MAC address is divided into two parts:

OUI (Organizationally Unique Identifier): The first 24 bits (3 bytes) identify the manufacturer or vendor. This portion is assigned by the IEEE Registration Authority.
Device Identifier: The last 24 bits (3 bytes) represent a unique number assigned by the manufacturer to the specific device.

For example, in the MAC address 00:1A:2B:3C:4D:5E:

00:1A:2B is the OUI (identifying the manufacturer)
3C:4D:5E is the device identifier (unique to the specific device)

Special Bits in MAC Addresses

Within the first byte of the MAC address, two special bits have specific meanings:

Universal/Local Bit (U/L Bit)

The second least significant bit (bit 1) of the first byte determines whether the address is universally administered (burned in by the manufacturer) or locally administered (assigned by software):

0 = Universally administered address (UAA)
1 = Locally administered address (LAA)

Individual/Group Bit (I/G Bit)

The least significant bit (bit 0) of the first byte indicates whether the address is an individual address (unicast) or a group address (multicast):

0 = Individual address (unicast)
1 = Group address (multicast)

For example, in a MAC address starting with 02:, the binary representation is 00000010, meaning it's a locally administered unicast address.

Special MAC Addresses

There are several special MAC addresses used for specific purposes:

MAC Address	Purpose
FF:FF:FF:FF:FF:FF	Broadcast address (sends to all devices on the network)
01:00:5E:xx:xx:xx	IPv4 multicast address
33:33:xx:xx:xx:xx	IPv6 multicast address
01:80:C2:00:00:00	Spanning Tree Protocol (STP) multicast address

How to Find Your Device's MAC Address

Finding the MAC address of your device varies by operating system:

Windows

Method 1: Open Command Prompt and enter ipconfig /all, then look for "Physical Address"

Method 2: Go to Settings > Network & Internet > Status > View your network properties

macOS

Method 1: Go to System Preferences > Network, select your connection, click "Advanced" and go to the "Hardware" tab

Method 2: Open Terminal and type ifconfig, then look for "ether"

Linux

Method 1: Open Terminal and type ifconfig or ip addr, then look for "ether" or "link/ether"

Method 2: Use the command cat /sys/class/net/*/address

iOS

Go to Settings > General > About > Wi-Fi Address

Android

Go to Settings > About Phone > Status > Wi-Fi MAC Address

Common Uses of MAC Addresses

MAC addresses are used in various networking contexts:

1. Network Access Control

MAC address filtering allows network administrators to create access control lists, permitting only authorized devices with specific MAC addresses to connect to a network.

2. DHCP Reservations

Network administrators can configure DHCP servers to always assign the same IP address to a device based on its MAC address.

3. Network Troubleshooting

MAC addresses help in identifying and resolving network connectivity issues by pinpointing specific devices on a network.

4. Device Tracking

MAC addresses can be used to track device movement within a network, particularly useful for Wi-Fi analytics in retail or public spaces.

MAC Address Limitations and Privacy Concerns

While MAC addresses are fundamental to networking, they come with certain limitations and privacy concerns:

MAC Spoofing

Most modern operating systems allow users to temporarily change their MAC address through software. This is called MAC spoofing and can be used for legitimate purposes (like troubleshooting) or malicious ones (like bypassing MAC filtering).

Privacy Implications

Since MAC addresses are unique and typically don't change, they can be used to track devices across different networks. This has led to privacy concerns, especially in public Wi-Fi environments.

MAC Randomization

To address privacy concerns, many modern devices (especially smartphones and laptops) implement MAC address randomization when scanning for Wi-Fi networks or connecting to new networks.

MAC Address Security

While MAC filtering can add a layer of security to your network, it should not be your only security measure because:

MAC addresses can be easily spoofed by attackers
MAC addresses are transmitted in clear text and can be captured
They don't provide any encryption or authentication

Always use strong encryption (WPA3) and other security measures in addition to MAC filtering.

MAC Address Lookup

The ability to look up a device's manufacturer based on its MAC address is a useful tool for network administrators and security professionals. The first three bytes (OUI portion) can be checked against the IEEE's database to identify the manufacturer.

At MACVerify, we provide a comprehensive MAC address lookup tool that allows you to quickly identify the manufacturer of any network device. Our database contains over 74,762 manufacturer entries from IEEE's official OUI listings and is updated daily.

To perform a MAC address lookup, simply enter the MAC address in our search tool on the homepage.

Conclusion

MAC addresses are fundamental building blocks of networking that enable devices to communicate on a local network. Understanding how they work, their format, and their purposes is essential for network administration, troubleshooting, and security.

While technology continues to evolve, particularly with the growth of wireless networking and the Internet of Things (IoT), MAC addresses remain a critical element in modern networking infrastructure.