Networking Concepts

The OSI model has seven layers: Physical (1), Data Link (2), Network (3), Transport (4), Session (5), Presentation (6), Application (7). Network+ expects you to map devices, protocols, and problems to the right layer — e.g., a bad cable is Layer 1, a MAC/switching issue is Layer 2, an IP/routing issue is Layer 3.

Data is encapsulated down the stack: data → segment (L4) → packet (L3) → frame (L2) → bits (L1), with each layer adding its header. On receipt the process reverses (de-encapsulation). Troubleshooting “bottom-up” (start at Layer 1) is a common, effective strategy.