CompTIA Network+ Network+ Troubleshooting Tools and Methods 3 — Questions and Answers
Question 1: A technician runs 'nslookup mail.company.com' and receives a different IP than expected. What should be checked next?
- The switch MAC address table
- DNS server records and potential DNS poisoning (Correct answer)
- The default gateway ARP entry
- DHCP lease duration
Correct answer: DNS server records and potential DNS poisoning
An unexpected DNS response could indicate stale DNS records or DNS cache poisoning that must be investigated on the DNS server.
Question 2: Which tool would a technician use to measure the exact length of a copper cable run and identify where a break occurs?
- Tone generator
- TDR (Time Domain Reflectometer) (Correct answer)
- Multimeter
- Loopback plug
Correct answer: TDR (Time Domain Reflectometer)
A TDR sends a signal down the cable and measures the time for reflection to calculate cable length and pinpoint faults.
Question 3: After replacing a NIC, a workstation cannot communicate with any host. Ping to 127.0.0.1 succeeds but ping to the default gateway fails. What is the MOST likely cause?
- Incorrect subnet mask
- The NIC driver is not installed correctly (Correct answer)
- DNS server is unreachable
- Incorrect VLAN assignment on the switch port
Correct answer: The NIC driver is not installed correctly
Loopback success confirms TCP/IP is functional, but failure to reach the gateway after a NIC replacement most likely means the driver is missing or faulty.
Question 4: A network map shows an unknown device with IP 192.168.1.254 that does not appear in DHCP leases. What tool would BEST identify this device?
- Packet sniffer
- Nmap port/OS scan (Correct answer)
- iperf bandwidth test
- Cable certifier
Correct answer: Nmap port/OS scan
Nmap can perform host discovery and OS fingerprinting to identify unknown devices on a network segment.
Question 5: A user reports intermittent packet loss. You run iperf between two hosts and see consistent 2% loss. What should you check NEXT?
- DNS TTL values
- Interface error counters on the switch ports (Correct answer)
- DHCP server pool exhaustion
- NTP synchronization
Correct answer: Interface error counters on the switch ports
Consistent measured packet loss points to a physical or link-layer issue best revealed by checking interface error counters on the connecting switch ports.
Question 6: Which protocol does the 'arp -a' command display information about?
- Layer 3 routing tables
- Cached IP-to-MAC address mappings (Correct answer)
- Active TCP connections
- DNS cache entries
Correct answer: Cached IP-to-MAC address mappings
The 'arp -a' command shows the local ARP cache, which maps IP addresses to MAC addresses learned on the local network segment.
Question 7: A technician uses a loopback plug on a switch port and the port LED shows link. What has been confirmed?
- The cable from the switch to the PC is good
- The switch port's physical transmit and receive circuits are functioning (Correct answer)
- The switch is properly configured for the correct VLAN
- Layer 3 routing is operational
Correct answer: The switch port's physical transmit and receive circuits are functioning
A loopback plug confirms the switch port can transmit and receive at the physical layer, isolating the port from the cable plant.
CompTIA Network+ Network+ Troubleshooting Tools and Methods 3
A technician runs 'nslookup mail.company.com' and receives a different IP than expected.
What should be checked next?