MAC Addressing

[!NOTE] This module explores the core principles of MAC Addressing, deriving solutions from first principles and hardware constraints to build world-class, production-ready expertise.

1. What is a MAC Address?

A Media Access Control (MAC) address is a unique identifier assigned to a Network Interface Controller (NIC) for use as a network address in communications within a network segment. It is also known as a Physical Address.

2. Structure (48-bits)

Usually represented in hexadecimal: 00:0A:95:9D:68:16.

  • OUI (Organizationally Unique Identifier): The first 24 bits. Identifies the manufacturer (e.g., Apple, Intel, Cisco).
  • NIC Specific: The last 24 bits. Assigned by the manufacturer to ensure uniqueness.

3. Address Types

  1. Unicast: Sent to a specific NIC.
  2. Multicast: Sent to a group of NICs (e.g., 01:00:5E:XX:XX:XX).
  3. Broadcast: Sent to EVERY NIC on the segment. The address is FF:FF:FF:FF:FF:FF.

4. Interactive: MAC Lookup

Identify the manufacturer.

Input MAC Address
Vendor: ?

5. The CAM Table (Content Addressable Memory)

A switch doesn’t broadcast every packet. It maintains a table of MAC Address → Port.

  1. Learning: When a packet arrives on Port 1 from MAC AAA, the switch remembers: AAA is on Port 1.
  2. Forwarding: When a packet comes for MAC AAA, the switch sends it only to Port 1.

[!NOTE] If the destination MAC is not in the table, the switch performs Flooding (sends to all ports except the source).