OSI Layers

The OSI (Open Systems Interconnection) model is a 7-layer reference model for network communications, used to describe the different levels of abstraction and functions in a network system.

1. Physical layer: responsible for the physical transmission of data over a network medium (e.g. copper or fiber cables).

2. Data link layer: responsible for reliable delivery of data frames over the physical layer.

3. Network layer: responsible for routing data packets between networks and providing end-to-end network communication.

4. Transport layer: responsible for end-to-end communication and ensuring reliable transmission of data between applications.

5. Session layer: responsible for establishing, maintaining, and tearing down communication sessions between applications.

6. Presentation layer: responsible for transforming data into a standard format for use by the application layer.

7. Application layer: responsible for providing application services to the user, such as email, file transfers, and web services.

The OSI model provides a common framework for understanding and describing the different aspects of network communication, and helps to separate the responsibilities and functions of different network components.

The layer in which a tool operates affects its functionality, security, and efficiency. Knowing which layer a tool operates at helps network administrators understand the tool's capabilities and limitations, and to choose the right tool for the job.

For example, Pomerium is better for HTTPS-based security because it is a layer 7 tool. Layer 4 tools such as StrongDM are better for TCP connections.