Computer Science/Network

MAC address

JTB 2025. 8. 1. 23:50

A MAC (Media Access Control) address is a unique identifier assigned to a network interface for communication at the data link layer (Layer 2) of the OSI model.

 

Key Characteristics:

  • It is a physical (hardware) address embedded into the Network Interface Card (NIC) of a device.
  • All devices connected to a network must have a MAC address to participate in communication.
  • The ARP (Address Resolution Protocol) is used to map an IP address to its corresponding MAC address.
  • Once the MAC address is determined, the data is forwarded to the network layer (Layer 3) for further processing.

How MAC Address Handling Works

 

  • The NIC (Network Interface Card) listens for incoming signals and converts them into Layer 2 data units (frames).
  • It then checks the destination MAC address of each incoming frame:
    • If the destination MAC matches the NIC’s own MAC address, the frame is accepted and passed to the upper layer.
    • If not, the frame is discarded.
    • If the destination is a broadcast or multicast address, the frame is processed as intended for the group and forwarded to the upper layer.

This mechanism ensures that only relevant data is processed by a device, maintaining efficiency and security within the local network.

 

MAC Address Structure

 

A MAC (Media Access Control) address is a 48-bit identifier typically represented as a 12-digit hexadecimal number.

 

Example format: 00:1A:2B:3C:4D:5E

 

The 48 bits are divided into two 24-bit parts:

  • OUI (Organizationally Unique Identifier) – First 24 bits
    • Assigned and managed by the IEEE
    • Identifies the manufacturer of the network interface card (NIC)
    • A manufacturer may be assigned multiple OUIs
  • UAA (Universally Administered Address) – Last 24 bits
    • Assigned by the manufacturer
    • Uniquely identifies each device produced by that manufacturer

 

Key Characteristics of MAC Addresses

  1. Globally Unique Identifier
    •    Each MAC address is designed to be unique across all network devices.
    •    The OUI ensures that no two manufacturers assign overlapping addresses.
  2. Relationship with the Network Layer
    •    MAC addresses operate at Layer 2 (Data Link Layer)
    •    IP addresses operate at Layer 3 (Network Layer)
    •    MAC is the physical address, while IP is the logical address
  3. Purpose and Usage
    •    Used for direct communication within a local network
    •    Enables frame delivery from one device to another over Ethernet or Wi-Fi
    •    Mapped from IP using ARP (Address Resolution Protocol)
  4. Notation Format
    •    Written as 6 pairs of hexadecimal digits separated by colons or hyphens
    •    Example: 00:1A:2B:3C:4D:5E or 00-1A-2B-3C-4D-5E
  5. Configuration and Mutability
    •    Factory-assigned MAC addresses are immutable in physical devices
    •    In virtualized environments, MAC addresses can be modified via software

MAC addresses play a critical role in Layer 2 communications, acting as unique hardware identifiers that ensure accurate data delivery on local networks.