MAC address

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.

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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

 

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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

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