A server administrator is investigating a critical application on a Windows Server that is intermittently failing to connect to its SQL database server. The application logs show 'Connection Timeout' errors. The SQL server is on a different subnet, but other applications on the same server can connect to other resources on the SQL server's subnet without issues. Basic `ping` and `telnet` to the SQL server's IP and port (1433) from the affected application server are successful. What is the MOST likely cause of the intermittent 'Connection Timeout' errors?
- ASQL server instance is overloaded or experiencing resource contention
- BNetwork firewall blocking port 1433 intermittently
- CDefault gateway misconfiguration on the application server
- DIncorrect DNS resolution for the SQL server hostname
Show answer & explanationAnswer & explanation
Correct answer: A. SQL server instance is overloaded or experiencing resource contention
If `ping` and `telnet` to the SQL server's IP and port are consistently successful, it rules out basic network connectivity, firewall blocking (consistently), and DNS issues (if connecting by IP). Intermittent 'Connection Timeout' errors, despite successful basic connectivity tests, strongly suggest that the SQL server itself is intermittently too busy or resource-constrained to accept new connections within the expected timeout period, indicating an overload or contention issue on the SQL server.
Why the other options are wrong
- B. If `telnet` to port 1433 is successful, the firewall is not blocking it. Intermittent blocking is less likely if other applications on the same server can connect to other resources on the SQL server's subnet.
- C. Default gateway misconfiguration would prevent *any* communication to other subnets, which is contradicted by successful `ping` and `telnet` attempts.
- D. DNS is not the issue as `ping` to IP works, and `telnet` to IP:port works. If connecting by hostname, `ping` by hostname would fail if DNS was the problem.
Database Connection Timeout
A database connection timeout occurs when a client application attempts to establish a connection to a database server but the server does not respond within a specified time limit.
- Can be caused by network latency, firewall, or server overload.
- Successful ping/telnet often points to server-side resource issues.
- Requires examining database server performance metrics.
Memory trick: Timeout means server's too tired to talk.