OSI Model
Seven-layer conceptual model for how network communication is structured — from physical bits to application data.
★★★★★5/5Network layer — DNS, CDN, load balancers, routing
How it works
The Open Systems Interconnection (OSI) model provides a universal framework for how data travels across a network. Each layer adds headers/trailers (encapsulation) on the way down and strips them (decapsulation) on the way up.
Layer 1 (Physical): bits on the wire. Layer 2 (Data Link): frames between nodes on the same network — MAC addresses. Layer 3 (Network): packets across networks — IP routing. Layer 4 (Transport): end-to-end delivery — TCP (reliable) / UDP (fast). Layer 5 (Session): session management. Layer 6 (Presentation): encoding, encryption, compression. Layer 7 (Application): HTTP, DNS, SMTP — what applications speak.
In practice, TCP/IP collapses OSI into 4 layers.
Why it matters
The OSI model is the shared vocabulary for every networking conversation. Understanding which layer a problem lives on is the first step to diagnosing it.
✓ When to use
- →Diagnosing network issues — identify which layer is failing
- →Designing network security (firewalls operate at L3/L4, WAFs at L7)
- →Understanding where load balancers (L4 vs L7) and TLS operate
✗ When NOT to use
- →The OSI model is a reference model, not an implementation choice
Trade-offs
Universal vocabulary for network communication
Real-world TCP/IP doesn't cleanly map to all 7 layers
In production
DDoS mitigation targets L3/L4 (volumetric) and L7 (application) attacks separately
Security Groups (L3/L4) and WAF (L7) map directly to OSI layers
Industry adoption
Related principles
Load Balancing
LiveDistribute incoming traffic across multiple servers to maximise throughput, minimise latency, and prevent overload.
CDN Architecture
LiveServe content from edge nodes geographically close to users, drastically reducing latency and origin load.
DNS Resolution
LiveTranslate human-readable domain names into IP addresses via a distributed, hierarchical lookup system.