MAC Addressing, Unicast vs Multicast, and Logical Link Control (LLC)
Every device connected to an Ethernet or Wi-Fi network has a unique hardware identity burned permanently into its Network Interface Card (NIC)—its MAC Address.
1. Anatomy of a MAC Address (Physical Address)
A MAC (Media Access Control) Address is a 48-bit (6-byte) physical address written as 12 hexadecimal digits separated by colons or hyphens:
Formula: Example: 00:1A:2B:3C:4D:5E
48-Bit MAC Address Structure
🏭 First 24 Bits: OUI (Vendor Code)
- Organizationally Unique Identifier (OUI)
- Assigned globally by the IEEE to hardware manufacturers (e.g., Apple, Intel, Cisco, Samsung).
- Identifies the company that built the network chip.
🔢 Last 24 Bits: NIC Serial Number
- Network Interface Controller Specific
- Assigned uniquely by the manufacturer to each individual card.
- Guarantees that no two network cards in the world have the exact same MAC address!
2. Types of MAC Addresses: Unicast, Multicast, and Broadcast
- Unicast Address: Sent to one specific destination device (e.g.,
00:1A:2B:3C:4D:5E). The least significant bit of the first byte is0. - Multicast Address: Sent to a specific group of subscribed devices (e.g., all smart TVs streaming a cricket match). The least significant bit of the first byte is
1. - Broadcast Address: Sent to every single computer on the entire local network! The broadcast MAC address is:
Formula: FF:FF:FF:FF:FF:FF (all 48 bits are 1s)
💡 DAVV Exam Tip
Question (5 Marks): “Explain the structure of a 48-bit MAC address. Differentiate between Unicast, Multicast, and Broadcast addresses.”
- Draw the 48-bit breakdown: 24 bits OUI (Manufacturer) + 24 bits Device Serial Number.
- Write the Broadcast MAC address:
FF:FF:FF:FF:FF:FF.