N10-009 Network Troubleshooting Practice Test 5 — 15 Questions

Question 1

A user reports that they cannot access the company's internal web application at https://apps.internal.company.com. The technician can ping the server's IP address (10.10.10.20) successfully and also successfully telnet to 10.10.10.20 on port 443. However, the web browser displays 'Unable to connect'. What is the most likely cause?

Accepted Answer

The browser is configured to use an incorrect proxy server. The technician can ping the server IP and telnet to port 443, proving the server is reachable and the HTTPS service is listening. However, the browser fails to load the page, which points to a client-side issue. An incorrect proxy server configuration in the browser would cause the browser to send requests to a proxy that cannot reach the internal server, resulting in 'Unable to connect' despite successful network-level connectivity tests.

Answer

The web server service is stopped

Answer

DNS resolution is failing for the FQDN

Answer

A firewall is blocking TCP port 443

Question 2

A technician is troubleshooting a wireless network that experiences intermittent disconnections. A spectrum analysis shows channel utilization consistently above 80% on the 2.4 GHz band. Which of the following is the most likely cause?

Accepted Answer

Too many access points are configured on the same or overlapping channels. A is correct because consistently high channel utilization above 80% on the 2.4 GHz band indicates co-channel or adjacent-channel interference, typically caused by too many access points (APs) operating on the same or overlapping channels (e.g., channels 1, 6, and 11 are non-overlapping in 802.11b/g/n). This leads to excessive contention, increased retransmissions, and intermittent disconnections as stations wait for clear channel access via CSMA/CA.

Answer

Access point output power is too high

Answer

Microwave ovens are interfering with the wireless signal

Answer

Client devices have weak signal strength

Question 3

A user reports that they cannot access any company resources. The technician runs 'ipconfig' and sees that the workstation has an IP address of 169.254.100.25 with a subnet mask of 255.255.0.0. The technician also notices that the 'Default Gateway' is blank. What is the most likely cause?

Accepted Answer

The DHCP server is unavailable or unreachable.. The IP address 169.254.100.25 with a subnet mask of 255.255.0.0 is an Automatic Private IP Addressing (APIPA) address, which Windows assigns when a DHCP client fails to obtain a lease. The blank Default Gateway confirms that no DHCP server responded, so the workstation cannot reach any company resources beyond its local subnet.

Answer

The DNS server is not responding.

Answer

The workstation has a static IP address configured.

Answer

The network cable is unplugged.

Question 4

A user reports that they can access the internet but cannot access the company's internal web application at https://intranet.company.local. The technician can ping the server's IP address (192.168.10.50) successfully from the user's workstation. However, when the technician runs 'nslookup intranet.company.local', it returns 'Non-existent domain'. What is the most likely cause?

Accepted Answer

The client's DNS server does not have a record for the internal domain.. The user can access the internet and ping the server's IP address, which confirms Layer 3 connectivity and that the web server is reachable. However, 'nslookup intranet.company.local' returns 'Non-existent domain', indicating that the DNS server used by the client does not have an A or CNAME record for that internal hostname. Since the browser relies on DNS resolution to translate the FQDN to an IP address, the failure to resolve the name prevents the web application from loading, even though the server itself is online and reachable.

Answer

The web server is not running on port 443.

Answer

A firewall is blocking traffic to the internal web server.

Answer

The hostname is misspelled in the browser.

Question 5

Users in a small office can access external websites normally, but they cannot reach the internal company wiki server at 192.168.10.25. A technician can successfully ping the server's IP address from a user's workstation. The DNS resolution for the wiki's hostname (wiki.company.local) returns the correct IP. The company's firewall permits HTTP traffic to the server. What is the most likely cause of the issue?

Accepted Answer

The web server service is not running or is listening on a different port. Since the technician can successfully ping the server's IP address from the user's workstation, Layer 3 connectivity is confirmed, ruling out routing or gateway issues. DNS resolution returns the correct IP, so name resolution is not the problem. The firewall permits HTTP traffic, so access control is not blocking the connection. The most likely cause is that the web server service (e.g., Apache, IIS) is not running or is listening on a non-standard port (e.g., 8080 instead of 80), preventing the HTTP request from reaching the service even though the host is reachable.

Answer

The default gateway on the server is misconfigured

Answer

The user's workstation has a duplicate IP address

Answer

The DNS cache on the workstation is poisoned

Question 6

A network technician is troubleshooting an issue where users on VLAN 20 can access internal servers and the default gateway but cannot reach any external websites. The router's ACL is configured to permit all outbound traffic. What is the most likely cause of this issue?

Accepted Answer

NAT is not configured or is misconfigured on the router. Since users can access internal servers and the default gateway, Layer 3 connectivity within the VLAN is working, and the router's ACL permits all outbound traffic. The inability to reach external websites while internal resources are reachable strongly indicates that Network Address Translation (NAT) is either not configured or misconfigured on the router. Without NAT, private IP addresses from VLAN 20 cannot be translated to a public IP, so return traffic from external web servers has no route back to the internal hosts.

Answer

The DNS server is unreachable from the VLAN

Answer

The DHCP server is not providing a default gateway

Answer

The switch port for the router is in the wrong VLAN

Question 7

A user reports that they can connect to the corporate Wi-Fi network but cannot access any network resources including the intranet and internet. The IP configuration shows an IP address of 169.254.25.100 with a subnet mask of 255.255.0.0. What is the most likely cause?

Accepted Answer

The DHCP server is unavailable or the request is not reaching it. The IP address 169.254.25.100 with a subnet mask of 255.255.0.0 is an Automatic Private IP Addressing (APIPA) address, which is assigned by the operating system when a DHCP server is unavailable or the DHCP request fails. Since the user can connect to Wi-Fi but cannot access any network resources, the most likely cause is that the DHCP server is not responding or the DHCP discover/offer/request/ack sequence is failing, leaving the device with a link-local address that cannot route to the corporate network or internet.

Answer

The DNS server is not responding

Answer

The subnet mask is incorrect

Answer

The switch port has port security enabled that has blocked the device

Question 8

A user reports that they can access the company's intranet website by IP address but not by its hostname (intranet.company.local). A technician checks the DNS server and finds that the A record exists and returns the correct IP. However, the user's browser still cannot resolve the hostname. Which of the following is the most likely cause?

Accepted Answer

The DNS cache on the user's workstation is corrupt.. The user can access the intranet by IP but not by hostname, which indicates that name resolution is failing. Since the DNS server has the correct A record, the issue is likely on the client side. A corrupt DNS cache on the workstation can cause the browser to use stale or invalid cached data, preventing successful resolution even though the authoritative DNS server returns the correct IP. Flushing the DNS cache with `ipconfig /flushdns` would resolve this.

Answer

The web server's certificate is expired.

Answer

The default gateway is misconfigured.

Answer

The file server is overloaded.

Question 9

A user reports that they can access the internet but cannot connect to an internal file server at IP address 192.168.1.50. The technician successfully pings the file server's IP address from the user's workstation. The file server is on the same subnet as the user. What is the most likely cause of this issue?

Accepted Answer

The file server's firewall is blocking the file-sharing protocol while allowing ICMP.. The technician can ping the file server (ICMP success) but the user cannot connect to it using the file-sharing protocol (e.g., SMB on TCP/445). This indicates network-layer reachability is fine, but the application-layer service is blocked. The most likely cause is the file server's host-based firewall (e.g., Windows Defender Firewall) allowing ICMP Echo Requests while blocking inbound SMB traffic, which is a common misconfiguration.

Answer

The file server has an incorrect default gateway configured.

Answer

The user's workstation has an incorrect DNS server configured.

Answer

The user's workstation has a duplicate IP address assigned.

Question 10

A network administrator configures a router-on-a-stick to route traffic between VLAN 10 and VLAN 20. Users in each VLAN can communicate within their own VLAN but cannot reach devices in the other VLAN. The router has subinterfaces configured, and the switch port connected to the router is configured as an access port in VLAN 1. What is the most likely cause of the inter-VLAN connectivity failure?

Accepted Answer

The switch port connected to the router is not configured as a trunk.. The router-on-a-stick design requires the switch port connecting to the router to be configured as a trunk port. This allows the switch to forward frames from multiple VLANs (VLAN 10 and VLAN 20) to the router's subinterfaces, each tagged with the appropriate 802.1Q VLAN ID. When the port is set as an access port in VLAN 1, it only accepts untagged frames from VLAN 1, so the router's subinterfaces for VLAN 10 and VLAN 20 never receive traffic, breaking inter-VLAN routing.

Answer

The router's subinterfaces are not configured with IP addresses.

Answer

The VLANs are not created on the switch.

Answer

The router's default route is missing.

Question 11

A user's computer obtains an IP address from DHCP, can ping the default gateway, but cannot access any external websites. The technician runs 'tracert 8.8.8.8' from the user's computer. The first hop shows the default gateway with low latency, but the second hop shows a timeout. What is the most likely cause?

Accepted Answer

The router's default route pointing to the ISP is missing or incorrectly configured.. The traceroute shows that the user's computer can reach the default gateway (first hop) but times out at the second hop, which is the ISP's router. This indicates that the local router does not have a valid default route pointing to the ISP, so it cannot forward traffic beyond the local subnet. Without a correct default route, packets destined for external networks (like 8.8.8.8) are dropped, even though the user's computer can ping the gateway and obtain an IP via DHCP.

Answer

The user's computer firewall is blocking outbound web traffic.

Answer

The DNS server is not resolving domain names.

Answer

The ISP's DNS server is unreachable.

Question 12

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?

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

Answer

Incorrect default gateway

Answer

Proxy server misconfiguration

Question 13

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

Answer

Co-channel interference

Answer

Insufficient DHCP scope

Question 14

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

Answer

Speed mismatch

Answer

Printer driver issues

Question 15

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

Answer

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

Answer

Interference from microwave ovens