The Open Systems Interconnection (OSI) reference model was created by the Internet Standards Organization (ISO) and is a reference model used for communication. Each of the seven different layers have 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 emails, 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 layer formats data into the character code, such as Unicode or ASCII. Encryption also works at this layer.
- Session Layer: This is where you would create a session, such as logging in and logging out.
- Transport Layer: Ports are...