Java.sql.SQLException: The TCP/IP connection to the host has failed.

Question

Hello. I hope you had a happy new year! Now its back to work.
I am having a problem connecting to a remote SQL Server DB. I am using NetBeans 5.5 and the latest J2EE. I am able to see the tables in the IDE and bind objects to data. But when I run it it gets this:
java.sql.SQLException: Error in allocating a connection. Cause: Connection could not be allocated because: The TCP/IP connection to the host has failed. java.net.ConnectException: Connection refused: no further information
at com.sun.gjc.spi.DataSource.getConnection(DataSource.java:100)
at com.sun.sql.rowset.internal.CachedRowSetXReader.connect(CachedRowSetXReader.java:344)
at com.sun.sql.rowset.internal.CachedRowSetXReader.readData(CachedRowSetXReader.java:126)
at com.sun.sql.rowset.CachedRowSetXImpl.execute(CachedRowSetXImpl.java:968)
at com.sun.sql.rowset.CachedRowSetXImpl.execute(CachedRowSetXImpl.java:1428)
I checked the SQL Server Configuration manager on that machine and TCP/IP connections are allowed. What else could be wrong?
Thank You.

Answer 1

"Connection refused" means that the client sends a packet saying "I would like to connect to port number NNNN please" to the server computer, and the server computer's OS sends the reply "there is no process listening to that port on the network interface you are using".
The database server is not running, or running but not listening to TCP/IP connections, or at a different port from what you think, or listening to only selected network interfaces (it is possible for a process to listen to a specific interface or a wildcard for all interfaces). A less likely scenario is that a firewall is sending the "connection refused" message.
First aid check list for "connection refused":
- Check host name in connect string.
- Check port number in connect string.
- Try numeric IP address of server host in connect string, in case name server is hosed.
- Are there any firewalls between client and server blocking the port.
- Check that the db server is running.
- Check that the db server is listening to the port. On the server, try: "telnet localhost the-port-number". Or "netstat -an", there should be a listening entry for the port. You need to configure the database to accept TCP connections; the server documentation or google should explain how.
- Try "telnet server-host-name the-port-number" from the client, to see if firewalls are blocking it.
- If "telnet" fails: try telnet with the numeric ip address.
- If "telnet" fails: does it fail immediately or after an obvious timeout? How long is the timeout?
- Does the server respond to "ping serverhost" or "telnet serverhost" or "ssh serverhost"?