Cisco CCNA OSI and TCP/IP Models 2 — Questions and Answers
Question 1: A network engineer needs to troubleshoot why two hosts can ping each other but cannot establish a Telnet session. Which OSI layer should be investigated first?
- Layer 1 - Physical
- Layer 3 - Network
- Layer 4 - Transport (Correct answer)
- Layer 2 - Data Link
Correct answer: Layer 4 - Transport
Ping operates at Layer 3, so if ping works, Layers 1-3 are functional; Telnet failures point to Layer 4 (TCP port 23) or above.
Question 2: Which TCP/IP model layer is responsible for logical addressing and routing between networks?
- Network Access
- Application
- Internet (Correct answer)
- Transport
Correct answer: Internet
The Internet layer of the TCP/IP model handles IP addressing and routing, equivalent to the OSI Network layer.
Question 3: What is the term for the data unit at the OSI Data Link layer?
- Segment
- Packet
- Frame (Correct answer)
- Bit
Correct answer: Frame
The Data Link layer (Layer 2) encapsulates data into frames, which include MAC addressing and error detection (FCS).
Question 4: Which OSI layer converts data between formats such as encryption, compression, and character encoding?
- Session (Layer 5)
- Application (Layer 7)
- Presentation (Layer 6) (Correct answer)
- Transport (Layer 4)
Correct answer: Presentation (Layer 6)
The Presentation layer (Layer 6) handles data translation, encryption/decryption, and compression between the application and network.
Question 5: In which scenario does the OSI Session layer play a critical role?
- Routing packets between VLANs
- Managing dialog control between two applications in a video conference (Correct answer)
- Assigning IP addresses via DHCP
- Encoding data into electrical signals
Correct answer: Managing dialog control between two applications in a video conference
The Session layer (Layer 5) establishes, manages, and terminates communication sessions, including dialog control for applications like video conferencing.
Question 6: A router receives a packet destined for a remote network. At which OSI layer does it make the forwarding decision?
- Layer 2
- Layer 4
- Layer 3 (Correct answer)
- Layer 1
Correct answer: Layer 3
Routers operate at Layer 3 (Network) and use the destination IP address in the packet header to make forwarding decisions.
Question 7: Which statement correctly describes encapsulation in the OSI model?
- Each layer removes header information added by the layer above it
- Each layer adds its own header (and sometimes trailer) to data received from the layer above (Correct answer)
- Data flows upward through the layers on the sending host
- The Application layer adds headers last before transmission
Correct answer: Each layer adds its own header (and sometimes trailer) to data received from the layer above
During encapsulation, each OSI layer on the sending host adds its own header (and trailer at Layer 2) to the data passed down from the layer above.
Cisco CCNA OSI and TCP/IP Models 2
A network engineer needs to troubleshoot why two hosts can ping each other but cannot establish a Telnet session.
Which OSI layer should be investigated first?