Cisco CCNA OSI and TCP/IP Models 4 — Questions and Answers
Question 1: A switch receives a frame with an unknown destination MAC address. What does it do?
- Drops the frame silently
- Sends an ARP request to find the destination
- Floods the frame out all ports except the one it was received on (Correct answer)
- Forwards the frame to the default gateway
Correct answer: Floods the frame out all ports except the one it was received on
When a switch receives a frame with an unknown unicast destination MAC, it floods the frame out all ports except the ingress port (unknown unicast flooding).
Question 2: At which OSI layer does a hub operate?
- Layer 2 - Data Link
- Layer 3 - Network
- Layer 1 - Physical (Correct answer)
- Layer 4 - Transport
Correct answer: Layer 1 - Physical
A hub operates at Layer 1 (Physical) and simply repeats electrical signals out all ports without examining MAC or IP addresses.
Question 3: Which field in the Ethernet frame is used at the OSI Data Link layer to detect transmission errors?
- Preamble
- Type/EtherType
- Frame Check Sequence (FCS) (Correct answer)
- Start Frame Delimiter (SFD)
Correct answer: Frame Check Sequence (FCS)
The Frame Check Sequence (FCS) uses a CRC algorithm to detect bit errors in the Ethernet frame at the Data Link layer.
Question 4: Which TCP/IP model layer corresponds to both the OSI Session and Presentation layers?
- Transport
- Network Access
- Internet
- Application (Correct answer)
Correct answer: Application
The TCP/IP Application layer combines the functions of OSI layers 5 (Session), 6 (Presentation), and 7 (Application).
Question 5: What type of address does the OSI Network layer use to deliver packets between networks?
- MAC address
- Port number
- Logical (IP) address (Correct answer)
- Physical address
Correct answer: Logical (IP) address
The Network layer (Layer 3) uses logical IP addresses to identify source and destination hosts across different networks.
Question 6: A network administrator notices that a host can communicate within its own subnet but cannot reach remote networks. Which OSI layer device is most likely misconfigured?
- Hub (Layer 1)
- Switch (Layer 2)
- Router (Layer 3) (Correct answer)
- Firewall (Layer 7)
Correct answer: Router (Layer 3)
Routers operate at Layer 3 and are responsible for forwarding traffic between different networks; a misconfigured default gateway or routing table would cause this symptom.
Question 7: Which protocol at the TCP/IP Internet layer is used to report error messages and operational information, such as host unreachable?
- ARP
- UDP
- ICMP (Correct answer)
- TCP
Correct answer: ICMP
ICMP (Internet Control Message Protocol) operates at the Internet layer and sends error messages such as 'Destination Unreachable' and is used by the ping utility.
Cisco CCNA OSI and TCP/IP Models 4
A switch receives a frame with an unknown destination MAC address.
What does it do?