📡 Networking: Interfaces & MAC Addresses

🔌 What are Network Interfaces?

A network interface is the point where a computing device connects to a network. It’s the hardware or software that handles the sending and receiving of data. Every device that connects to a network—like a laptop, smartphone, or server—has at least one network interface.

📂 Types of Network Interfaces

1. Physical Interfaces These are hardware components built for network connectivity.

   • Ethernet Card (NIC): A card with a port for a network cable, used for wired connections on a Local Area Network (LAN).
   • Wi-Fi Adapter: The hardware that enables a device to connect to a wireless network (WLAN).
   • Bluetooth Adapter: Allows devices to connect wirelessly over short distances, often used for peripherals like keyboards and mice.
   • Cellular Modem: Used in mobile devices to connect to cellular networks (e.g., 4G, 5G).
   • Fiber Optic Interface: Used for high-speed internet connections, typically in enterprise environments.
   • USB Network Adapter: A portable adapter that connects to a USB port to provide network connectivity, often used for laptops or devices without built-in Ethernet ports.

2. Virtual Interfaces These are software-based interfaces that don’t correspond to a physical piece of hardware.

   • Loopback Interface (lo): A virtual interface that always points back to the device itself (often with the IP 127.0.0.1). It’s used for testing and local service communication.
   • VPN Interface: When you connect to a VPN, your system creates a virtual interface that represents the secure connection tunnel.

🏷️ What is a MAC Address?

A MAC (Media Access Control) address is a unique hardware identifier assigned to a physical network interface by the manufacturer. It’s often called the physical address or hardware address.

🔢 MAC Address Format

A MAC address is a 48-bit number, typically written as six pairs of hexadecimal characters separated by colons or hyphens.

• Example: 3C:A6:2B:9A:E4:F1
• Structure:
  • OUI (Organizationally Unique Identifier): The first three pairs (3C:A6:2B) identify the manufacturer (e.g., Apple, Intel).
  • Device Identifier: The last three pairs (9A:E4:F1) are a unique serial number assigned by the manufacturer.

🆚 MAC Address vs. IP Address

This is a critical distinction in networking.

In simple terms, a switch uses MAC addresses to send data to the correct device on a local network, while a router uses IP addresses to send data to the correct network across the internet.