100-150 Question 225
Single answerA user reports they cannot access a web server hosted on a remote network. You attempt to troubleshoot by using the following commands from the user's device: ping, tracert, and nslookup. The ping and tracert commands fail, but the nslookup command successfully resolves the server's domain name to an IP address. What is the most likely cause of the issue?
- A
The web server is offline and not responding to any requests.
- B
A firewall is blocking ICMP traffic between the user's device and the web server.
- C
The user's device does not have a valid default gateway configured.
- D
DNS resolution is failing for the web server's domain name.
Show answer and explanation
Correct answer: B
Explanation
The failure of ping and tracert suggests that ICMP traffic is being blocked, likely by a firewall, while the success of nslookup confirms that DNS resolution is working. Firewalls often block ICMP traffic for security reasons but allow DNS queries to function normally.
- A. Incorrect.
If the web server were offline, nslookup would also fail to resolve the domain name because the DNS server would not respond with the IP address.
- B. Correct.
Firewalls often block ICMP traffic, which is used by ping and tracert, while allowing DNS queries (used by nslookup) to pass through. This explains why ping and tracert fail but nslookup works.
- C. Incorrect.
If the user's device did not have a valid default gateway, the nslookup command would still work for DNS resolution because it does not require a gateway to query the local DNS server. This does not explain the failed ping and tracert.
- D. Incorrect.
DNS resolution is not failing because the nslookup command successfully resolves the web server's domain name to an IP address. This indicates DNS is functioning correctly.