Cisco Certified Support Technician (CCST) NetworkingIP ServicesHard
A web server administrator notices that the server's logs show requests coming from various IP addresses, but the DNS resolver logs on the server are empty. However, users report no issues accessing the website by its domain name. What is the most probable reason for the empty DNS resolver logs?
- AThe client devices are resolving DNS, not the web server itself.
- BThe web server has a pre-populated DNS cache.
- CThe DNS server is offline.
- DThe web server is using its local hosts file for name resolution.
Show answer & explanationAnswer & explanation
Correct answer: A. The client devices are resolving DNS, not the web server itself.
When a client accesses a web server by its domain name, the client performs the DNS resolution to get the server's IP address. The client then connects directly to the web server's IP. The web server itself does not typically perform DNS lookups for incoming connections, unless it needs to resolve the client's hostname (reverse DNS), which is often disabled or not logged by default.
Why the other options are wrong
- B. A pre-populated DNS cache would explain some lookups not hitting the resolver, but not consistently empty logs if the server was doing lookups for every request.
- C. If the DNS server were offline, users wouldn't be able to reach the website by domain name.
- D. While possible, it's unlikely a web server would rely solely on a hosts file for all incoming connections, and this wouldn't explain why clients can resolve names.
Client-Side DNS Resolution
The process where an end-user device (client) performs DNS lookups to resolve a domain name into an IP address before initiating a connection to a server.
- DNS resolution is typically done by the client.
- Servers receive connections to their IP, not their domain name.
- Server's DNS logs might be empty if it doesn't initiate outbound lookups.
Memory trick: Client Connects, Server Sees IP, Not Name.