CompTIA Network+ Network+ OSI Model Layers and Functions 3 — Questions and Answers
Question 1: Which OSI layer PDU (Protocol Data Unit) is called a 'segment'?
- Data Link layer
- Network layer
- Transport layer (Correct answer)
- Session layer
Correct answer: Transport layer
The Transport layer's PDU is called a segment, which contains port numbers and sequencing information.
Question 2: A network engineer is troubleshooting a connectivity issue and wants to verify physical signal integrity on the cable. Which OSI layer should they focus on?
- Layer 1 (Correct answer)
- Layer 2
- Layer 3
- Layer 4
Correct answer: Layer 1
The Physical layer (Layer 1) deals with the transmission of raw bits over a physical medium, including signal integrity.
Question 3: Which protocol at the Application layer is used to translate domain names to IP addresses?
- FTP
- DNS (Correct answer)
- SMTP
- HTTP
Correct answer: DNS
DNS (Domain Name System) operates at the Application layer and resolves human-readable domain names to IP addresses.
Question 4: During data transmission, which OSI layer adds a trailer containing a Frame Check Sequence (FCS) for error detection?
- Transport layer
- Network layer
- Physical layer
- Data Link layer (Correct answer)
Correct answer: Data Link layer
The Data Link layer adds both a header and a trailer; the trailer contains the FCS used for error detection.
Question 5: A VPN concentrator terminates encrypted tunnels at which OSI layer when using IPSec in tunnel mode?
- Layer 2
- Layer 3 (Correct answer)
- Layer 4
- Layer 5
Correct answer: Layer 3
IPSec in tunnel mode operates at the Network layer (Layer 3), encrypting entire IP packets and encapsulating them in new IP packets.
Question 6: Which of the following best describes the role of the Session layer in the OSI model?
- Converts data formats and handles encryption
- Establishes, manages, and terminates communication sessions (Correct answer)
- Provides reliable end-to-end data transfer
- Routes packets between networks
Correct answer: Establishes, manages, and terminates communication sessions
The Session layer (Layer 5) is responsible for establishing, managing, and terminating sessions between applications.
Question 7: An application developer is building a network program and needs to ensure data is delivered reliably with error checking. Which Transport layer protocol should they use?
- UDP
- ICMP
- ARP
- TCP (Correct answer)
Correct answer: TCP
TCP (Transmission Control Protocol) provides reliable, connection-oriented delivery with error checking and acknowledgments.
CompTIA Network+ Network+ OSI Model Layers and Functions 3
Which OSI layer PDU (Protocol Data Unit) is called a 'segment'?