Physical Addressing

Overview

Physical addressing, commonly known as MAC (Media Access Control) addressing, is the foundation of network device identification at the hardware level. This 48-bit addressing scheme provides a unique identifier for each network interface card (NIC) in existence. Unlike logical addressing, physical addresses are permanently burned into network hardware during manufacturing, creating a globally unique identifier that facilitates data transmission at the data link layer of networks. This addressing system is crucial for local network communications and serves as the basis for frame delivery between directly connected devices.

Detailed Explanation

Physical addressing is fundamental to network communications, operating at Layer 2 (Data Link Layer) of the OSI model. The system uses MAC addresses, which are 48-bit (6-byte) numbers typically represented in hexadecimal format.

MAC Address Structure

  • First 24 bits: Organizationally Unique Identifier (OUI)
    • Assigned to manufacturers by IEEE
    • Identifies the hardware manufacturer
  • Last 24 bits: Network Interface Controller (NIC) specific
    • Unique number assigned by manufacturer
    • Ensures global uniqueness of the address

Characteristics of Physical Addressing

  1. Uniqueness

    • Each MAC address is globally unique
    • No two network interfaces should have the same address
    • Managed through IEEE registration process

  2. Permanence

    • Burned into ROM of network interface
    • Cannot be changed through software (though some NICs allow spoofing)
    • Remains constant regardless of network location

  3. Flat Addressing Structure

    • No hierarchy unlike IP addressing
    • Direct one-to-one mapping
    • No routing information embedded

Address Resolution Protocol (ARP)

Physical addressing works in conjunction with ARP to:

  • Map IP addresses to MAC addresses
  • Maintain ARP cache tables
  • Enable communication between network devices
  • Resolve addressing conflicts

Frame Processing

  1. Frame Creation

    • Source MAC address automatically inserted
    • Destination MAC address determined through ARP
    • Frame check sequence added for error detection

  2. Frame Delivery

    • Frames examined by all devices on local network
    • Only device with matching MAC processes frame
    • Broadcast addresses received by all devices

Physical Addressing in Different Networks

  1. Ethernet Networks

    • 48-bit MAC addresses standard
    • Unicast, multicast, and broadcast addressing supported
    • Used in frame headers for delivery

  2. Wireless Networks

    • Similar MAC addressing scheme
    • Additional features for wireless communication
    • Important for WiFi security mechanisms

References

  • IEEE Standards Association - MAC Address Block Large (MA-L)
  • Stallings, W. (2016). Data and Computer Communications (10th ed.)
  • IEEE 802.3 Ethernet Working Group Documentation