OSI Model

Learn about the fundamental networking framework that determines the various stages in which data is handled across a network

Task 1 What is the OSI Model?

The OSI model (or Open Systems Interconnection Model) is an absolute fundamental model used in networking. This critical model provides a framework dictating how all networked devices will send, receive and interpret data.

One of the main benefits of the OSI model is that devices can have different functions and designs on a network while communicating with other devices. Data sent across a network that follows the uniformity of the OSI model can be understood by other devices.

[…]

Question: What does the “OSI” in “OSI Model” stand for?

Answer: Open Systems Interconnection

Question: How many layers (in digits) does the OSI model have?

Answer: 7

Question: What is the key term for when pieces of information get added to data?

Answer: encapsulation

Task 2 Layer 7 - Application

The application layer of the OSI model is the layer that you will be most familiar with. This familiarity is because the application layer is the layer in which protocols and rules are in place to determine how the user should interact with data sent or received.

[…]

Question: What is the name of this Layer?

Answer: Application

Question: What is the technical term that is given to the name of the software that users interact with?

Answer: Graphical User Interface

Task 3 Layer 6 - Presentation

Layer 6 of the OSI model is the layer in which standardisation starts to take place. Because software developers can develop any software such as an email client differently, the data still needs to be handled in the same way — no matter how the software works.

[…]

Question: What is the name of this Layer?

Answer: Presentation

Question: What is the main purpose that this Layer acts as?

Answer: Translator

Task 4 Layer 5 - Session

Once data has been correctly translated or formatted from the presentation layer (layer 6), the session layer (layer 5) will begin to create a connection to the other computer that the data is destined for. When a connection is established, a session is created. Whilst this connection is active, so is the session.

[…]

Question: What is the name of this Layer?

Answer: Session

Question: What is the technical term for when a connection is successfully established?

Answer: Session

Question: What is the technical term for “small chunks of data”?

Answer: Packets

Task 5 Layer 4 - Transport

Layer 4 of the OSI model plays a vital part in transmitting data across a network and can be a little bit difficult to grasp. When data is sent between devices, it follows one of two different protocols that are decided based upon several factors:

• TCP
• UDP

Let’s begin with TCP. The Transmission Control Protocol (TCP). Potentially hinted by the name, this protocol is designed with reliability and guarantee in mind. This protocol reserves a constant connection between the two devices for the amount of time it takes for the data to be sent and received.

[…]

Question: What is the name of this Layer?

Answer: Transport

Question: What does TCP stand for?

Answer: Transmission Control Protocol

Question: What does UDP stand for?

Answer: User Datagram Protocol

Question: What protocol guarantees the accuracy of data?

Answer: TCP

Question: What protocol doesn’t care if data is received or not by the other device?

Answer: UDP

Question: What protocol would an application such as an email client use?

Answer: TCP

Question: What protocol would an application that downloads files use?

Answer: TCP

Question: What protocol would an application that streams video use?

Answer: UDP

Task 6 Layer 3 - Network

The third layer of the OSI model (network layer) is where the magic of routing & re-assembly of data takes place (from these small chunks to the larger chunk). Firstly, routing simply determines the most optimal path in which these chunks of data should be sent.

[…]

Question: What is the name of this Layer?

Answer: Network

Question: Will packets take the most optimal route across a network? (Y/N)

Answer: Y

Question: What does the acronym “OSPF” stand for?

Answer: Open Shortest Path First

Question: What does the acronym “RIP” stand for?

Answer: Routing Information Protocol

Question: What type of addresses are dealt with at this layer?

Answer: IP Addresses

Task 7 Layer 2 - Data Link

The data link layer focuses on the physical addressing of the transmission. It receives a packet from the network layer (including the IP address for the remote computer) and adds in the physical MAC (Media Access Control) address of the receiving endpoint. Inside every network-enabled computer is a Network Interface Card (NIC) which comes with a unique MAC address to identify it.

[…]

Question: What is the name of this Layer?

Answer: Data Link

Question: What is the name of the piece of hardware that all networked devices come with?

Answer: Network Interface Card

Task 8 Layer 1 - Physical

This layer is one of the easiest layers to grasp. Put simply, this layer references the physical components of the hardware used in networking and is the lowest layer that you will find. Devices use electrical signals to transfer data between each other in a binary numbering system (1’s and 0’s).

[…]

Question: What is the name of this Layer?

Answer: Physical

Question: What is the name of the numbering system that is both 0’s and 1’s?

Answer: Binary

Question: What is the name of the cables that are used to connect devices?

Answer: Ethernet Cables

Task 9 Practical - OSI Game

Can you escape the OSI dungeon? Climb the levels in the correct order to escape the dungeon and reveal the flag! (Can you beat our staff high score of 19 seconds?)

Click the “View Site” button on the right to start.

Note: If you are in MAC then play the game using Option Key + Space to go inside open door (layer),

And If you are in Windows play with Alt Key + Space to go inside open door (layer).

Question: Escape the dungeon to retrieve the flag. What is the flag?

Answer: THM{OSI_DUNGEON_ESCAPED}

Task 10 Continue Your Learning: Packets & Frames

Continue your learning by joining the “Packets and Frames” room.

Question: Join the “Packets and Frames” room.

Answer: No Answer needed

Room link: https://tryhackme.com/room/osimodelzi