N10-009 Network Troubleshooting Practice Test 6 — 15 Questions

Question 1

A user reports they can access internal servers and the default gateway but cannot reach external websites. The technician checks the router's ACL and finds a rule that permits all outbound traffic. What is the most likely cause?

Choose an answer to begin — your selection is scored in the full session.

Accepted Answer

NAT configuration issue. The user can access internal servers and the default gateway, indicating Layer 3 connectivity within the local network. However, external websites are unreachable. Since the ACL permits all outbound traffic, the issue is not a blocked outbound rule. The most likely cause is a NAT configuration issue, such as missing or incorrect IP masquerading (PAT) on the router's outside interface, which prevents internal private IP addresses from being translated to a public IP address for internet access.

Answer

DNS resolution failure

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Incorrect default gateway

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Proxy server misconfiguration

Question 2

Users in a warehouse report that their wireless tablets lose connectivity when moving near large metal racks. The signal strength remains high but throughput drops significantly. What is the most likely cause?

Accepted Answer

Multipath interference. When wireless signals reflect off large metal surfaces, multiple copies of the signal arrive at the receiver at slightly different times, causing multipath interference. This phase cancellation effect corrupts the signal, forcing the 802.11 MAC layer to retransmit frames, which drastically reduces throughput even though the received signal strength indicator (RSSI) remains high. The metal racks in the warehouse act as reflective surfaces, creating a classic multipath environment.

Answer

Signal attenuation

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Co-channel interference

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Insufficient DHCP scope

Question 3

A switch is connected to a network printer. The switch port is manually configured for 100 Mbps and full duplex. The printer is configured for auto-negotiation. The link is up, but there are many FCS errors on the switch port. What is the most likely cause?

Accepted Answer

Duplex mismatch. The most likely cause is a duplex mismatch. The switch port is manually set to full duplex, while the printer is using auto-negotiation. When one side is manually configured and the other is set to auto-negotiation, the auto-negotiating side fails to detect the manual setting and defaults to half duplex. This mismatch causes collisions and frame check sequence (FCS) errors on the full-duplex side, as the half-duplex side does not properly handle simultaneous transmission.

Answer

Bad Ethernet cable

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Speed mismatch

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Printer driver issues

Question 4

A user's laptop frequently disconnects from the Wi-Fi network when they move to the conference room. Other devices in the conference room maintain stable connections. The laptop shows a strong signal in the conference room. What is the most likely cause?

Accepted Answer

Laptop's wireless adapter driver is outdated or faulty. The laptop disconnects only when moving to the conference room, while other devices remain stable, ruling out environmental issues. A strong signal but frequent disconnects points to a client-side problem, most commonly an outdated or faulty wireless adapter driver that fails to handle roaming or power-save transitions properly.

Answer

AP channel is congested

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Laptop is using the 5 GHz band while the AP uses 2.4 GHz

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Interference from microwave ovens

Question 5

A network administrator is deploying a new PoE security camera. The camera is connected to a PoE-enabled switch port, but the camera does not power on. The administrator confirms the switch port has PoE enabled and the cable is tested and functional. What is the most likely cause?

Accepted Answer

The camera requires 802.3bt (PoE++), but the switch only supports 802.3af (PoE).. The camera requires 802.3bt (PoE++) which can deliver up to 60W or 90W, but the switch only supports 802.3af (PoE) which provides a maximum of 15.4W per port. Since the camera's power demand exceeds the switch's capability, the camera will not power on even though PoE is enabled and the cable is functional.

Answer

The cable is a crossover cable.

Answer

The port is configured as an access port.

Answer

The camera is using a passive PoE injector.

Question 6

A user reports intermittent connectivity issues. The technician runs ping tests and notices that pings to the default gateway sometimes fail and sometimes succeed. While pinging, the technician observes that some replies have high latency. Which tool should the technician use to analyze the path and identify where packets are being delayed?

Accepted Answer

traceroute / tracert. Traceroute (tracert on Windows) is the correct tool because it sends packets with incrementing Time-to-Live (TTL) values to map the entire Layer 3 path from source to destination. By measuring the round-trip time (RTT) for each hop, it can pinpoint exactly which router or link is introducing high latency or packet loss, addressing the intermittent connectivity and delayed replies observed in the ping tests.

Answer

nslookup

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ipconfig

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arp

Question 7

Users in a remote branch office report that they cannot access the company's cloud-based applications. The network administrator notices that the edge router's WAN interface is up but the branch's default route points to a next-hop IP that is unreachable. The administrator can ping the ISP's gateway IP from the router. What is the most likely cause?

Accepted Answer

The static default route has an incorrect next-hop IP. The scenario describes a static default route configured with a next-hop IP that is unreachable. The WAN interface is up and the ISP gateway is reachable (as confirmed by the ping), but the router cannot forward traffic to the cloud because the static route points to an incorrect next-hop address. This is a classic static route misconfiguration where the next-hop IP does not match the ISP gateway or is not in the directly connected subnet.

Answer

The routing protocol is not redistributing the default route

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The WAN interface is administratively down

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The firewall is blocking traffic to the cloud

Question 8

A user can ping the default gateway (192.168.1.1) but cannot access the internet (e.g., ping 8.8.8.8 fails). The user's IP is correctly configured as 192.168.1.10/24. What should the technician check next?

Accepted Answer

Check the router's default route configuration. Since the user can ping the default gateway (192.168.1.1), Layer 2 and Layer 3 connectivity within the local subnet is working, and the PC's IP configuration is correct. The failure to reach 8.8.8.8 indicates that the router does not have a valid path to external networks, which is typically provided by a default route (0.0.0.0/0). Checking the router's default route configuration is the logical next step because without it, the router cannot forward traffic destined for non-local networks.

Answer

Check the PC's DNS server settings

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Verify the subnet mask on the PC

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Examine the switch port VLAN assignment

Question 9

A user's computer is unable to obtain a DHCP lease after connecting to a new switch port. The user's computer displays an IP address in the 169.254.x.x range. Other users on the same VLAN can obtain IP addresses successfully. The switch port is configured for 802.1X authentication. What is the most likely cause?

Accepted Answer

The user's computer has not authenticated via 802.1X and is placed in a restricted VLAN.. When 802.1X authentication is enabled on a switch port, the port initially operates in an unauthorized state, restricting traffic to only EAPoL (802.1X) frames. If the user's computer fails to authenticate (e.g., due to missing supplicant, incorrect credentials, or certificate issues), the switch can place the port into a restricted or guest VLAN that lacks a DHCP server or is isolated from the production network. The 169.254.x.x address (APIPA) indicates the client could not reach a DHCP server, which aligns with being placed in a VLAN without DHCP services.

Answer

The DHCP server has exhausted its address pool.

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The switch port is in a blocked state due to a spanning tree loop.

Answer

The network cable is faulty.

Question 10

A user reports that they can access internal websites but cannot access any external websites. Other users in the same subnet can access external sites. The user's IP configuration shows a correct IP, subnet mask, and default gateway. What is the most likely cause?

Accepted Answer

The proxy server settings are incorrect.. The user can access internal websites but not external ones, while other users in the same subnet have no issues. This points to a client-specific configuration problem rather than a network-wide issue. Incorrect proxy server settings on the user's machine can prevent external HTTP/HTTPS traffic from being routed correctly, even though internal traffic (which may bypass the proxy) works fine.

Answer

The DNS server is not reachable.

Answer

The default gateway is misconfigured.

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The web browser has a corrupted cache.

Question 11

A technician connects a user's workstation to a switch port. The cable passes a physical test, and the switch port LED is green, but the workstation cannot establish a network connection. What is the most likely cause?

Accepted Answer

Duplex mismatch between the workstation and the switch. A duplex mismatch occurs when one side of a link is set to full-duplex and the other to half-duplex, often due to a failed autonegotiation. Even though the cable passes a physical test and the switch port LED is green (indicating link at Layer 1), the mismatch causes excessive collisions and frame errors at Layer 2, preventing successful network communication. The workstation cannot establish a connection because the switch and NIC are not coordinating their transmission/reception timing correctly.

Answer

Incorrect VLAN assignment on the switch port

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The workstation has a static IP address in the wrong subnet

Answer

A faulty cable

Question 12

Users in VLAN 10 cannot obtain IP addresses from the DHCP server located in VLAN 20. The router interface for VLAN 10 has an ip helper-address 192.168.20.5 command configured, and users can ping the DHCP server IP (192.168.20.5) from the router. However, users receive APIPA addresses. What is the most likely cause?

Accepted Answer

The DHCP server does not have a scope configured for the 192.168.1.0/24 subnet (VLAN 10). The ip helper-address command on the router correctly forwards DHCPDISCOVER broadcasts from VLAN 10 to the DHCP server at 192.168.20.5. Since users can ping the server from the router, Layer 3 connectivity exists. However, the DHCP server must have a scope (or address pool) for the subnet of the requesting clients (192.168.1.0/24) to offer an IP address; without it, the server ignores the request, and clients fall back to APIPA (169.254.x.x).

Answer

The router's ip helper-address is configured on the wrong interface

Answer

The switch port connecting users is configured as a trunk instead of an access port

Answer

The router's ACL is blocking DHCP offers from the server

Question 13

A user can ping the default gateway (192.168.1.1) but cannot ping the external IP address 8.8.8.8. Other users on the same subnet can ping 8.8.8.8 without issue. The user's IP configuration is correct: IP 192.168.1.10/24, default gateway 192.168.1.1, DNS 8.8.8.8. What is the most likely cause?

Accepted Answer

The computer's firewall is blocking outbound ICMP. The user can ping the default gateway (192.168.1.1) but not the external IP 8.8.8.8, while other users on the same subnet can ping 8.8.8.8 without issue. This isolates the problem to the user's specific host, not the network infrastructure. A local firewall on the user's computer blocking outbound ICMP (Internet Control Message Protocol) traffic would prevent ping to external IPs while still allowing local subnet communication, as ICMP is often restricted by default in some security policies.

Answer

The router is missing a default route to the internet

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The DNS server is not resolving the hostname

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The network cable is loose or faulty

Question 14

A user reports that they cannot access the internet. The user's workstation has an IP address of 192.168.1.100/24, with a default gateway of 192.168.1.1. The user can ping the default gateway but cannot ping 8.8.8.8. Other users on the same subnet can ping 8.8.8.8. The technician checks the switch and sees the user's port is up. What should the technician check next?

Accepted Answer

Check the workstation's IP configuration for a misconfigured default gateway or DNS. Since the user can ping the default gateway (192.168.1.1) but not 8.8.8.8, while other users on the same subnet can reach 8.8.8.8, the issue is isolated to this workstation. The most likely cause is a misconfigured default gateway (e.g., wrong IP or subnet mask) or DNS settings, as the gateway is reachable but traffic is not being forwarded correctly. Option B directly addresses checking the workstation's IP configuration for these misconfigurations, which is the logical next step after verifying local connectivity.

Answer

Check the router's routing table for a route to the internet

Answer

Check the DNS server configuration on the workstation

Answer

Check the switch port for VLAN misconfiguration

Question 15

Users on a VLAN report intermittent network disconnections lasting a few seconds. The network technician checks the switch and notices a high number of CRC errors on the port connecting to the core switch. The cable test passes. What is the most likely cause?

Accepted Answer

Duplex mismatch between the two switches. A duplex mismatch causes one side to send frames while the other is still transmitting, leading to collisions that are interpreted as CRC errors on the receiving interface. Since the cable test passes, the physical layer is fine, and the intermittent nature (lasting seconds) matches the symptom of a duplex mismatch where the half-duplex side backs off after collisions, causing brief outages.

Answer

STP reconvergence due to topology change

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Broadcast storm caused by a loop

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Faulty SFP transceiver on the core switch