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MAC Addresses Explained (Physical Addressing)

Networking Fundamentals: The 0 to Hero Guide

Lesson 26: MAC Addresses Explained (Physical Addressing)

We move down to Layer 2 (Data Link) to discuss the physical address: the MAC address.

What is a MAC Address?

MAC stands for Media Access Control. It is the hardware address assigned to every Network Interface Card (NIC) by the manufacturer. It is a unique identifier used for local communication (within a LAN segment).

Key Characteristics:

  1. Format: A 48-bit address, typically displayed as 12 hexadecimal digits (e.g., AA:BB:CC:DD:EE:FF) or (e.g., AABB.CCDD.EEFF).
  2. Physical Address: Unlike the IP address, the MAC address is permanently burned into the NIC's firmware (though it can be spoofed).
  3. Local Scope: MAC addresses are only relevant for devices talking to each other on the same network segment. Routers do not forward frames based on MAC addresses; they rely on IP addresses.

Structure of the MAC Address

The 48 bits are divided into two parts:

  • OUI (Organizationally Unique Identifier): The first 24 bits (the first six hex digits). This identifies the manufacturer of the NIC (e.g., Cisco, Intel).
  • Vendor Assigned Identifier: The last 24 bits. This is a unique serial number assigned by the manufacturer, ensuring that no two NICs in the world share the same MAC address.

text AA:BB:CC : DD:EE:FF ---OUI---- : --Serial--

Practical Example: When your laptop talks to the switch, it uses the MAC address. When your laptop talks to a website across the internet, it uses the IP address.