What Is a MAC Address?
A MAC address (Media Access Control address) is a unique hardware identifier permanently assigned to a device's network interface card (NIC) by the manufacturer. It operates at Layer 2 (Data Link Layer) of the OSI model and is used to identify devices within a local network (LAN). Unlike IP addresses — which are logical and can change — a MAC address is tied to the physical hardware itself.
Where Is the MAC Address Stored in Hardware?
The EEPROM chip permanently stores the MAC address. The network controller reads it at startup.
Inside a Wi-Fi SoC, the MAC address is written once into OTP ROM during chip fabrication — it cannot be erased.
What Does a MAC Address Look Like?
A MAC address is 48 bits long, represented as 12 hexadecimal digits. It is commonly written in three formats:
00:1A:2B:3C:4D:5E00-1A-2B-3C-4D-5E001A.2B3C.4D5EMAC Address Structure — OUI + Device ID
A MAC address is split into two 24-bit halves, each with a distinct purpose.
OUI (Organizationally Unique Identifier)
The first 6 hexadecimal characters form the OUI, which is assigned by the IEEE (Institute of Electrical and Electronics Engineers). Each manufacturer registers a unique OUI prefix. This is how tools like our MAC Vendor Lookup can identify who made a device just from the first half of its MAC address.
00:00:0CCisco Systems, IncF8:FF:C2Apple, Inc.8C:8D:28Intel CorporateDevice Identifier
The last 6 hexadecimal characters are assigned by the manufacturer to uniquely identify each individual device. Two devices from the same manufacturer share the same OUI but have different Device IDs, making the full 48-bit MAC address globally unique — in theory.
Where Is a MAC Address Used?
MAC addresses operate at Layer 2 (Data Link Layer) of the OSI model and handle local network communication. They never travel beyond your local network — routers strip Layer 2 headers when forwarding packets to other networks.
LAN Communication
Devices on the same network segment use MAC addresses to address Ethernet frames to each other.
Switch Forwarding
Ethernet switches maintain MAC address tables to forward frames to the correct port.
ARP (Address Resolution)
ARP maps IP addresses to MAC addresses so packets can be delivered on the local segment.
DHCP Reservations
Routers use MAC addresses to assign the same IP address to a specific device every time it connects.
MAC Filtering
Wi-Fi routers can allow or block devices based on their MAC address as an access control mechanism.
Network Troubleshooting
Network engineers use MAC addresses to identify and trace specific devices within a network.
How MAC Addresses Are Used for Device Communication
When a device wants to communicate on a LAN, it uses ARP (Address Resolution Protocol) to resolve the destination IP address to a MAC address. The Layer 2 switch then learns these MAC addresses and forwards Ethernet frames only to the correct port — making communication efficient.
📖 How MAC addresses work: ARP + Switch MAC Learning →MAC Address vs IP Address
MAC and IP addresses are often confused. They serve different purposes at different layers of the network stack.
Can a MAC Address Be Changed?
While MAC addresses are burned into hardware, the operating system can override what MAC address is broadcast on the network — a technique known as MAC spoofing. Additionally, modern operating systems now use MAC address randomization by default to improve privacy on public Wi-Fi.
iOS 14+
Uses a randomized MAC per Wi-Fi network by default to prevent cross-hotspot tracking.
Android 10+
Randomizes MAC address per-network by default. Can be switched to device MAC in Wi-Fi settings.
Windows 10 / 11
Supports random hardware addresses per Wi-Fi network. Toggle in network adapter advanced settings.
macOS Ventura+
Rotates the MAC address periodically while connected to the same network for enhanced privacy.
MAC randomization means OUI lookups on randomized addresses won't return meaningful vendor information — the OUI prefix belongs to the device OS, not the hardware manufacturer. Locally administered addresses (LAA) have the second-least-significant bit of the first byte set to 1.
How to Find Your MAC Address
ipconfig /allLook for Physical Address under your network adapter
ifconfig en0 | grep etherOr use System Settings → Network → Details → Hardware
ip link showLook for the 'link/ether' field on your active interface
Who Assigns MAC Addresses?
The IEEE (Institute of Electrical and Electronics Engineers) manages the global MAC address registry. Manufacturers apply for and purchase OUI blocks, which the IEEE tracks in the publicly available MA-L (MAC Address Block Large) registry.
MA-L (Large)
16.7 million addresses per OUI. Used by most manufacturers. Costs ~$3,185 USD.
MA-M (Medium)
4,096 addresses per block. Suitable for smaller volume manufacturers.
MA-S (Small)
256 addresses per block. For very small-scale or niche device manufacturers.
Why Use a MAC Vendor Lookup?
A MAC vendor lookup tool lets you identify the hardware manufacturer of any device on your network instantly. Common use cases include:
- Identifying unknown devices on your home or office Wi-Fi
- Verifying equipment during network audits
- Confirming manufacturer when a device shows up in router logs
- Security investigations — spotting unexpected or spoofed devices
- Network documentation and asset management
Frequently Asked Questions
Summary
- A MAC address is a 48-bit hardware identifier assigned by the manufacturer to a device's network interface card.
- It operates at Layer 2 (Data Link Layer) of the OSI model and is only used within local networks.
- The first 24 bits (OUI) identify the manufacturer; the last 24 bits are a unique device identifier.
- MAC addresses are used for LAN communication, ARP, DHCP reservations, switch forwarding, and MAC filtering.
- Unlike IP addresses, MAC addresses don't travel across the internet and don't change with network location.
- Modern operating systems randomize MAC addresses to improve privacy on public Wi-Fi networks.
- The IEEE manages OUI assignment through the MA-L, MA-M, and MA-S registry programs.