OSI – reference model

The Open Systems Interconnection (OSI) reference model was created by the Internet Standards Organization (ISO) and it is a reference model used for communication. Each of the seven different layers has different protocols and responsibilities. The Security+ exam focuses mainly on layers 2, 3, and 7:

Figure 1: OSI reference model

Here is a brief summary of each layer:

  • Application layer: Applications, such as HTTP for accessing the web or SMTP for accessing email, are launched here. The Web Application Firewall (WAF), whose job it is to protect web-based applications, operates at this layer.
  • Presentation layer: The presentation ...

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