CompTIA Network+ Network+ OSI Model and Data Encapsulation 2 — Questions and Answers
Question 1: A network engineer is troubleshooting a connectivity issue and finds that MAC addresses are not being resolved correctly. Which OSI layer is responsible for MAC address resolution?
- Network layer
- Data Link layer (Correct answer)
- Physical layer
- Transport layer
Correct answer: Data Link layer
The Data Link layer (Layer 2) handles MAC addresses and frame delivery on the local network segment.
Question 2: During data encapsulation, what term describes the data unit at the Transport layer?
- Frame
- Packet
- Segment (Correct answer)
- Bit
Correct answer: Segment
At the Transport layer (Layer 4), the data unit is called a segment (for TCP) or datagram (for UDP).
Question 3: Which OSI layer is responsible for establishing, managing, and terminating sessions between applications?
- Presentation layer
- Application layer
- Transport layer
- Session layer (Correct answer)
Correct answer: Session layer
The Session layer (Layer 5) manages dialog control and session establishment, maintenance, and termination.
Question 4: A packet is received with a TTL value of 0. Which OSI layer processes TTL and causes the packet to be discarded?
- Data Link layer
- Network layer (Correct answer)
- Transport layer
- Session layer
Correct answer: Network layer
The Network layer (Layer 3) processes TTL; when it reaches 0, the router discards the packet and sends an ICMP Time Exceeded message.
Question 5: Which layer of the OSI model converts data into a format suitable for transmission, including encryption and compression?
- Application layer
- Session layer
- Presentation layer (Correct answer)
- Transport layer
Correct answer: Presentation layer
The Presentation layer (Layer 6) handles data translation, encryption, and compression to ensure data is in a usable format.
Question 6: A technician captures network traffic and notices that data is being transferred using port 443. Which OSI layer is associated with port numbers?
- Network layer
- Data Link layer
- Transport layer (Correct answer)
- Application layer
Correct answer: Transport layer
Port numbers are a Transport layer (Layer 4) concept used to identify specific processes or services on a host.
Question 7: In the OSI model, de-encapsulation occurs at the receiving host. In what order are headers removed?
- Physical → Data Link → Network → Transport → Session → Presentation → Application (Correct answer)
- Application → Presentation → Session → Transport → Network → Data Link → Physical
- Transport → Network → Data Link → Physical → Session → Presentation → Application
- Network → Transport → Data Link → Session → Presentation → Application → Physical
Correct answer: Physical → Data Link → Network → Transport → Session → Presentation → Application
De-encapsulation proceeds from the bottom up — Physical, Data Link, Network, Transport, Session, Presentation, Application — stripping each layer's header as data moves up the stack.
CompTIA Network+ Network+ OSI Model and Data Encapsulation 2
A network engineer is troubleshooting a connectivity issue and finds that MAC addresses are not being resolved correctly.
Which OSI layer is responsible for MAC address resolution?