Understanding MAC Addresses

A Media Access Control (MAC) address is a unique identifier assigned to network interfaces for communications on the physical network segment. It's embedded in network hardware, like Ethernet cards, at the time of manufacture.

MAC addresses are 48-bits long, expressed as 12 hexadecimal digits. The first half, also known as the Organizationally Unique Identifier (OUI), identifies the manufacturer. The second half is the Network Interface Controller (NIC) specific to the device.

Though MAC addresses are supposed to be globally unique, manufacturers reusing addresses and software MAC spoofing can lead to duplicates in practice. This can create network security challenges and potential data leakage risks.

Contrary to popular belief, MAC addresses can be changed or spoofed using software. This is often used for privacy reasons or to bypass access controls, illustrating that MAC addresses, while hardware-based, are not immutable.

The seventh bit in a MAC address's first octet distinguishes between globally (0) and locally (1) administered addresses. Locally administered addresses are typically assigned manually by network administrators and are not factory-default.

MAC addresses can indicate multicast transmissions. If the least significant bit of the first octet is 1, the frame is destined for multiple hosts. This allows efficient data distribution to multiple devices simultaneously.

With the Internet of Things (IoT) expansion, the potential for MAC address exhaustion is real. However, the IEEE has considered a 64-bit MAC address to ensure sufficient unique addresses for billions of devices worldwide.