Cisco CCNA Basic Switching Concepts 3 — Questions and Answers
Question 1: How does a switch build its MAC address table?
- By sending ARP requests to all devices
- By reading the source MAC address of incoming frames (Correct answer)
- By reading the destination MAC of outgoing frames
- By querying a DHCP server for MAC-to-IP mappings
Correct answer: By reading the source MAC address of incoming frames
A switch learns MAC addresses by examining the source MAC address field of frames received on each port and recording the port association.
Question 2: What is the default aging time for dynamic MAC address entries on a Cisco switch?
- 60 seconds
- 180 seconds
- 300 seconds (Correct answer)
- 600 seconds
Correct answer: 300 seconds
Cisco switches default to a 300-second (5-minute) aging timer for dynamically learned MAC address table entries.
Question 3: Which switching method reads only the first 64 bytes of a frame before forwarding?
- Store-and-forward
- Cut-through
- Fragment-free (Correct answer)
- Adaptive
Correct answer: Fragment-free
Fragment-free switching reads the first 64 bytes to check for collision fragments before forwarding, balancing error detection and latency.
Question 4: On a Cisco switch, which command displays the MAC address table?
- show ip arp
- show mac address-table (Correct answer)
- show interfaces
- show cam table
Correct answer: show mac address-table
The 'show mac address-table' command displays all learned, static, and secure MAC address entries on a Cisco switch.
Question 5: A switch port is in full-duplex mode. Which statement is true?
- CSMA/CD is active on that port
- Collisions can still occur
- The port can send and receive simultaneously (Correct answer)
- The port speed is halved compared to half-duplex
Correct answer: The port can send and receive simultaneously
Full-duplex ports use separate transmit and receive paths, allowing simultaneous bidirectional communication and eliminating collisions.
Question 6: What does the 'switchport mode access' command configure on a Cisco switch port?
- Sets the port as a trunk carrying multiple VLANs
- Forces the port to belong to a single VLAN and not negotiate trunking (Correct answer)
- Enables VTP on the port
- Configures the port for inter-VLAN routing
Correct answer: Forces the port to belong to a single VLAN and not negotiate trunking
'switchport mode access' statically sets the port as an access port carrying only one VLAN and disables DTP negotiation.
Question 7: Which protocol can cause a loop-free Layer 2 topology by blocking redundant paths?
- EIGRP
- Spanning Tree Protocol (STP) (Correct answer)
- VLAN Trunking Protocol (VTP)
- CDP
Correct answer: Spanning Tree Protocol (STP)
Spanning Tree Protocol (STP) prevents Layer 2 loops by placing redundant switch ports into a blocking state.
Cisco CCNA Basic Switching Concepts 3
How does a switch build its MAC address table?