← All Learn guides Networking fundamentals

The OSI model

The OSI model splits networking into seven layers, from the raw signal on a cable up to the apps you use. When something breaks, knowing the layer tells you where to look.

What it doesExamples
7 · ApplicationWhat apps use to talkHTTP, DNS, SMTP
6 · PresentationFormats and encrypts dataTLS, JSON, JPEG
5 · SessionOpens and keeps conversationsSockets, RPC
4 · TransportReliable delivery between portsTCP, UDP
3 · NetworkRoutes between networksIP, ICMP
2 · Data linkMoves frames on a local networkEthernet, Wi-Fi, MAC
1 · PhysicalSends the raw signalsFibre, copper, radio
Memory trick

All People Seem To Need Data Processing (layers 7 to 1).

Where DevOps engineers debug most

  • Layer 7: HTTP errors and DNS problems
  • Layer 4: ports, firewalls and security groups
  • Layer 3: IP addresses, subnets and routing

Why it matters for your career

Networking questions come up in almost every cloud, DevOps and security interview. The OSI model is the usual starting point.

Keep learning

Containers vs VMsCloud infrastructureContainers vs VMsKubernetes basicsContainer orchestrationKubernetes basicsIncident response rolesWhen production breaksIncident response roles
Chat with us