The OSI and TCP/IP Models

The OSI and TCP/IP models are core networking models that represent systems’ communication. These two models are highly similar. In fact, they are practically the same except for the fact that layers 5, 6, and 7 of the OSI model are equivalent to layer 4 on the TCP/IP model, and layers 1 and 2 on the OSI model are equivalent to layer 1 on the TCP/IP model. In this article, we will use the OSI model to explain. It is important for cybersecurity professionals to understand these models to understand the different risks and defenses that come with different layers.

The OSI Model:

• Layer 1: Physical: data as electrical signals in wires
• Layer 2: Data Link: data begins to be formatted into packets, communication between devices begins (switches are in this layer)
• Layer 3: Network: routing to different destinations begins, communication outside the LAN (routers are in this layer and are absolutely crucial here)
• Layer 4: Transport: regulates communication in regards to protocols and ports, as well as checking for packet formatting errors
• Layer 5: Session: sessions (active connections between devices) are started/stopped to allow data in and out
• Layer 6: Presentation: also known as the syntax layer, data is uniformly formatted in preparation for use by the end/destination node
• Layer 7: Application: final presentation of data in user applications