OSI Model
The OSI model is a seven-layer reference model used to describe network communication. Real protocols do not always fit perfectly into one layer, but the model is useful for troubleshooting and security analysis.
The OSI model is a seven-layer reference model used to describe network communication. Real protocols do not always fit perfectly into one layer, but the model is useful for troubleshooting and security analysis.
| Layer | Name | Typical examples |
|---|---|---|
| 7 | Application | HTTP, DNS, SMTP |
| 6 | Presentation | Encoding, encryption formats |
| 5 | Session | Session establishment and management |
| 4 | Transport | TCP, UDP |
| 3 | Network | IP, routing |
| 2 | Data Link | Ethernet, MAC addressing |
| 1 | Physical | Cables, radio signals, hardware |
How to use it
When a connection fails, work through the layers. Is the interface connected? Does the device have a valid address? Can packets reach the destination? Is the transport port open? Does the application respond correctly?
For security, the model helps describe where a control or attack operates. A firewall may filter network and transport information, while an application firewall inspects higher-level requests.