This content originally appeared on DEV Community and was authored by Aisalkyn Aidarova
OSI Model Overview
The OSI (Open Systems Interconnection) model standardizes how network communication happens between devices.
It divides data transmission into 7 layers, each responsible for specific tasks — from sending electrical signals to displaying web pages.
The Seven Layers (Simplified with DevOps Focus)
| Layer | Name | Key Function | DevOps Perspective |
|---|---|---|---|
| 1 | Physical | Sends raw bits over cables, fiber, or radio signals. | When setting up servers (on-prem or cloud), DevOps ensures proper networking hardware or virtual network interfaces (ENIs, VPCs). |
| 2 | Data Link | Organizes bits into frames; uses MAC addresses for local delivery. | When configuring EC2 security groups, VPC subnets, or Docker bridge networks, you indirectly work with this layer. |
| 3 | Network | Routes packets across networks using IP addresses. | DevOps configures VPCs, subnets, CIDR blocks, and route tables — all belong here. Tools like ping, traceroute, and ip route operate at this layer. |
| 4 | Transport | Ensures reliable delivery with TCP or fast, connectionless transfer with UDP. | Understanding ports (HTTP-80, HTTPS-443) and load balancers (ALB/NLB) is critical. Monitoring latency or dropped packets (e.g., netstat, ss, curl -v) happens here. |
| 5 | Session | Manages and maintains communication sessions between applications. | In APIs, SSH, or web sockets, DevOps ensures stable sessions using reverse proxies (Nginx) or session persistence in load balancers. |
| 6 | Presentation | Translates, encrypts, or compresses data (e.g., SSL/TLS, JSON, JPEG). | SSL certificates, HTTPS termination, and data encoding in pipelines (base64, gzip) relate to this layer. |
| 7 | Application | Provides services directly to users (HTTP, FTP, SMTP, DNS). | DevOps deploys and monitors applications at this layer—web servers (Nginx, Apache), DNS setups, CI/CD delivery of app code. |
Practical Example — Visiting YouTube
- Application: Browser uses HTTP/HTTPS to request the YouTube page.
- Presentation: Data encrypted via TLS.
- Session: Connection maintained between your browser and YouTube servers.
- Transport: TCP ensures reliable delivery of video data.
- Network: IP routing directs packets globally.
- Data Link: Frames delivered via MAC addresses in your LAN or Wi-Fi.
- Physical: Data turned into electrical or radio signals over Ethernet or Wi-Fi.
Why OSI Matters for DevOps
- Troubleshooting: Knowing which layer fails helps isolate issues — e.g., DNS (Layer 7) vs. routing (Layer 3).
- Infrastructure setup: VPCs, subnets, and gateways map to layers 2–3.
- Security: Firewalls, SSL certificates, and IAM policies relate to Layers 3–7.
-
Monitoring: Tools like Wireshark,
tcpdump,netstat, and Prometheus metrics target different OSI layers.
This content originally appeared on DEV Community and was authored by Aisalkyn Aidarova