The OSI Model is one of the most important networking concepts on the CompTIA A+ exam.
It breaks networking into 7 layers so we can understand how data moves from one device to another.
Memory Trick:
All People Seem To Need Data Processing
Cables, signals, voltage, connectors.
Example: Ethernet cables, fiber, Wi-Fi signals.
MAC addresses and switching.
Devices: Switches.
IP addresses and routing.
Devices: Routers.
TCP and UDP live here.
Controls reliability and port numbers.
Opens, manages, and closes connections.
Encryption, formatting, compression.
User-facing protocols like HTTP, FTP, SMTP.
No link light? → Layer 1 problem.
169.254 address? → Layer 3 (DHCP issue).
Website not loading but ping works? → Layer 7 (DNS issue).