Cisco CCNA OSI and TCP/IP Models 3 — Questions and Answers
Question 1: Which OSI layer is responsible for flow control and error recovery using mechanisms like windowing and acknowledgments?
- Network (Layer 3)
- Data Link (Layer 2)
- Transport (Layer 4) (Correct answer)
- Session (Layer 5)
Correct answer: Transport (Layer 4)
The Transport layer (Layer 4) provides end-to-end flow control via windowing and reliable delivery through acknowledgment and retransmission.
Question 2: How many layers does the TCP/IP model have compared to the OSI model?
- The TCP/IP model has 5 layers; OSI has 7
- Both models have 7 layers
- The TCP/IP model has 4 layers; OSI has 7 (Correct answer)
- The TCP/IP model has 3 layers; OSI has 5
Correct answer: The TCP/IP model has 4 layers; OSI has 7
The TCP/IP model has 4 layers (Application, Transport, Internet, Network Access), while the OSI model has 7 layers.
Question 3: A technician captures traffic and sees a PDU with source and destination MAC addresses but no IP header. At which OSI layer was this PDU created?
- Layer 1 - Physical
- Layer 3 - Network
- Layer 2 - Data Link (Correct answer)
- Layer 4 - Transport
Correct answer: Layer 2 - Data Link
MAC addresses are used at Layer 2 (Data Link), and frames at this layer do not contain IP headers.
Question 4: Which protocol operates at the TCP/IP Application layer and is used to resolve hostnames to IP addresses?
- ARP
- OSPF
- DNS (Correct answer)
- ICMP
Correct answer: DNS
DNS (Domain Name System) operates at the Application layer of the TCP/IP model and resolves fully qualified domain names to IP addresses.
Question 5: During de-encapsulation on a receiving host, in what order does processing occur?
- Layer 7 → Layer 4 → Layer 3 → Layer 2 → Layer 1
- Layer 1 → Layer 2 → Layer 3 → Layer 4 → Layer 7 (Correct answer)
- Layer 4 → Layer 3 → Layer 2 → Layer 1 → Layer 7
- Layer 7 → Layer 1 → Layer 2 → Layer 3 → Layer 4
Correct answer: Layer 1 → Layer 2 → Layer 3 → Layer 4 → Layer 7
De-encapsulation on the receiving host processes data from the Physical layer (1) upward through the layers to the Application layer (7).
Question 6: Which two layers of the OSI model are combined into the Network Access layer of the TCP/IP model?
- Physical and Network
- Data Link and Network
- Physical and Data Link (Correct answer)
- Session and Transport
Correct answer: Physical and Data Link
The TCP/IP Network Access layer combines OSI's Physical layer (Layer 1) and Data Link layer (Layer 2) into a single layer.
Question 7: Which OSI layer uses port numbers to identify specific applications or services on a host?
- Network (Layer 3)
- Session (Layer 5)
- Transport (Layer 4) (Correct answer)
- Application (Layer 7)
Correct answer: Transport (Layer 4)
The Transport layer (Layer 4) uses port numbers in TCP and UDP headers to multiplex multiple application streams on the same host.
Cisco CCNA OSI and TCP/IP Models 3
Which OSI layer is responsible for flow control and error recovery using mechanisms like windowing and acknowledgments?