N10-009 Network Troubleshooting Practice Questions

Question 1

A user reports that they cannot access an internal web server at http://intranet.company.local but can access other internet websites. The technician runs ping intranet.company.local and receives replies successfully. Which tool should the technician use next to isolate the issue?

Accepted Answer

nslookup. The current explanation states that a successful `ping intranet.company.local` points to a name resolution failure. This is incorrect. If `ping intranet.company.local` receives replies successfully, it means the hostname *did* resolve to an IP address, and the server is reachable via ICMP. Therefore, name resolution is not the problem. The issue is more likely related to the web server service not running, a firewall blocking HTTP/HTTPS traffic to the server, or the hostname resolving to an *incorrect* IP address (though the explanation explicitly states 'failure' rather than 'incorrect resolution'). `nslookup` would only be the next step if the `ping` command failed to resolve the hostname or if the technician suspected an incorrect IP resolution despite successful ping.

Answer

tracert

Answer

netstat

Answer

ipconfig

Question 2

A technician is troubleshooting a failed ping to a specific website's IP address. The user can browse other websites without issue, and nslookup on the user's workstation returns the correct IP address for the website. Which of the following is the most likely cause?

Accepted Answer

The website server is blocking ICMP requests.. The most likely cause is that the website server is blocking ICMP echo request (ping) traffic. Many servers and firewalls block ICMP for security while still allowing HTTP/HTTPS traffic, so a failed ping does not mean the website is down. Because other websites are reachable and DNS resolved correctly, the default gateway, DNS, and subnet mask are unlikely to be the problem.

Answer

The default gateway is misconfigured.

Answer

The DNS server is not resolving the domain name.

Answer

The subnet mask is incorrect.

Question 3

A user can access a website by its IP address (e.g., 203.0.113.5) but cannot access it by its domain name (example.com). Other users on the same subnet can access the website by domain name. Which of the following should the technician check FIRST?

Accepted Answer

Check the local hosts file. The issue is isolated to a single user who can reach the website by IP but not by domain name, while other users on the same subnet have no problem. This indicates a client-side DNS resolution problem. The first thing to check is the local hosts file (e.g., C:\Windows\System32\drivers\etc\hosts) for any incorrect or outdated entries that might be overriding DNS resolution. If the hosts file has an incorrect mapping for example.com, the browser will use that instead of querying the DNS server, causing the failure. Checking DNS server configuration is appropriate if the hosts file is clean.

Answer

Check the DNS server configuration on the network

Answer

Check the website's DNS records

Answer

Check the user's browser proxy settings

Question 4

A technician is troubleshooting a user's inability to connect to a server. The technician runs 'tracert' from the user's workstation and sees that traffic stops at a particular router. The last hop shows a timeout. Which of the following is the most likely cause?

Accepted Answer

The next hop router is unreachable from that router.. The 'tracert' command relies on ICMP Time Exceeded messages from intermediate routers to map the path. When traffic stops at a particular router and the next hop shows a timeout, it indicates that the router cannot forward the packet to the next hop, meaning the next hop router is unreachable. This is the most direct cause because the traceroute fails to receive a response from the next hop, not because the destination is off or ICMP is blocked.

Answer

The destination server is powered off.

Answer

The router is blocking ICMP echo requests.

Answer

There is a routing loop.

Question 5

A network technician is troubleshooting a user's inability to connect to the network. The switch port is configured with port security with the default maximum of one MAC address. The user connects a computer and a VoIP phone to the port using the phone's built-in switch. Which of the following will MOST likely occur?

Accepted Answer

The port will go into errdisable state. With the default port security configuration, the switch port allows only one MAC address. When the VoIP phone connects, its own MAC address is learned first. The computer then connects through the phone's built-in switch, presenting a second MAC address, which violates the security policy. This triggers a security violation, and by default the port is placed into the errdisable state.

Answer

The phone will work but the computer will not

Answer

Both devices will work because the phone uses a different MAC

Answer

The switch will allow only the first learned MAC and block the second

Question 6

A technician is troubleshooting a user's inability to access the internet. The user can successfully ping the default gateway and internal servers, but cannot ping a public IP address such as 8.8.8.8. The technician checks the firewall logs and confirms that outbound ICMP traffic to 8.8.8.8 is permitted. Which of the following is the most likely cause of the issue?

Accepted Answer

Missing default route on the router. The user can ping the default gateway and internal servers, which confirms that Layer 2 and Layer 3 connectivity within the local network is working. However, the inability to ping a public IP (8.8.8.8) indicates that traffic is not being forwarded beyond the local subnet. A missing default route on the router means the router does not know where to send packets destined for external networks, so it drops them. Since outbound ICMP is permitted on the firewall, the issue is routing, not filtering.

Answer

Incorrect DNS server configuration on the workstation

Answer

Incorrect subnet mask on the workstation

Answer

Malware on the workstation is blocking ICMP traffic

Question 7

A network technician is troubleshooting a workstation that intermittently loses network connectivity. The link LED on the switch port is blinking slowly. The technician checks the cable and it appears fine. Which of the following is the most likely cause?

Accepted Answer

Duplex mismatch. Intermittent connectivity with a cable that appears physically fine is often caused by a duplex mismatch, where one side is configured for full duplex and the other for half duplex. This mismatch can cause collisions, CRC errors, and retransmissions, resulting in sporadic packet loss even though the link remains up. LED indicators vary by vendor and are not a reliable universal diagnostic; the connectivity pattern itself is the stronger clue.

Answer

Incorrect VLAN assignment

Answer

Bad cable

Answer

Spanning Tree blocking

Question 8

A user reports intermittent inability to access websites. When the issue occurs, the user can ping external IP addresses (e.g., 8.8.8.8) but cannot ping domain names like google.com. The user's IP configuration shows a DNS server address of 8.8.8.8. What is the most likely cause?

Accepted Answer

The DNS server is reachable but not responding due to high load.. The user can ping external IP addresses (e.g., 8.8.8.8) but cannot resolve domain names like google.com, which indicates that IP connectivity is working but DNS resolution is failing. Since the DNS server address is 8.8.8.8 and the user can ping it, the server is reachable; however, intermittent failures suggest the server is overwhelmed and dropping or not responding to queries. This matches the symptom of a reachable but unresponsive DNS server due to high load, where ICMP (ping) succeeds but UDP/53 DNS queries time out.

Answer

The default gateway is down.

Answer

The corporate firewall is blocking UDP port 53.

Answer

The user's machine has a corrupted DNS cache.

Question 9

A technician is troubleshooting a connectivity issue. The technician can successfully ping the IP address of a web server (10.10.10.10) from a client, but the client cannot access the web page. Firewall rules allow HTTP traffic. At which OSI layer is the issue most likely occurring?

Accepted Answer

Application layer (Layer 7). Since the client can successfully ping the web server's IP address (10.10.10.10), Layer 3 (Network) connectivity is verified, as ICMP operates at Layer 3 and uses IP. While ping does not verify Layer 4 (Transport) connectivity, the explicit mention that firewall rules allow HTTP traffic suggests that Layer 4 connectivity for HTTP is not being blocked. Therefore, the failure to access the web page points to an issue at Layer 7 (Application), such as a misconfigured web server (e.g., HTTP 404, incorrect document root), a missing or incorrect Host header in the HTTP request, or an application-layer proxy or authentication problem that prevents the HTTP transaction from completing successfully after the TCP connection is established.

Answer

Session layer (Layer 5)

Answer

Transport layer (Layer 4)

Answer

Network layer (Layer 3)

Question 10

Users at a remote branch office cannot access internet resources. The branch's edge router shows that the WAN interface is up. The default route is configured to point to next-hop 192.0.2.2, but the admin can successfully ping 192.0.2.1 from the router. What is the most likely cause?

Accepted Answer

The default route is missing or has an incorrect next-hop IP. The explanation states that the admin 'cannot reach 192.0.2.2 (the next-hop)', which is a critical piece of information not provided in the question stem. The stem only mentions successfully pinging 192.0.2.1. Without explicit confirmation that 192.0.2.2 is unreachable, the explanation's justification for the default route being the most likely cause is based on an unstated assumption. If 192.0.2.2 is reachable, other options like NAT configuration or firewall rules could be equally or more likely causes for internet access issues.

Answer

The router's WAN interface is configured with the wrong subnet mask

Answer

NAT is not configured on the router

Answer

A firewall on the router is blocking outbound traffic

Network Troubleshooting

N10-009 Network Troubleshooting — Key Topics

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