One machine on network cannot connect to SQL 2005

Question

I've got a small Windows network with 3 machines. One of them has SQL 2005 installed. As of last week, the other two machines have had no problems connecting to the SQL instance.

Today, one machine - running Vista, if that matters - all of a sudden cannot connect. I get the generic message saying "A network-related or instance-specific error occurred while establishing a connection to SQL Server. The server was not found or was not accessible. Verify that the instance name is correct and that SQL Server is configured to allow remote connections."

I'm pretty sure everything is set up correctly on the SQL 2005 box, because the third computer on the network still connects with no problem.

Vista computer has no firewalls set up, nothing has changed with the exception that I created a connection to a VPN a few days ago. When connected to the VPN, local network connectivity is hosed, but I've double checked many times that I am NOT connected to the VPN when trying to access SQL Server. I mention this only because it's the only thing I can think of that's changed.

I've rebooted all computers many times. No change.

I'm connecting via SQL Integrated Security. The login works fine from the third machine.

One other weird thing on the Vista box. Occasionally - maybe 5% of the time - it'll connect, but then when trying to access a table (like, just right clicking and choosing "open") it pauses then gives an "unspecified error."

Any ideas? I'm totally perplexed. This has been working for about 18 months without any errors, and I can't think of anything that's changed other than the VPN connection mentioned above. And just to reiterate - I am definitely NOT connected to the VPN when I'm getting this error.

Answer 1

Check the protocols used to connect ot SQL Server; I'm wondering whether it's trying to communicate over Named Pipes rather than TCP/IP (speaking from recent experience -- I had an issue with Named Pipes that went away when I disabled Named Pipes and enabled TCP/IP).

You can check this on the server with the SQL Server Configuration Tool, and see which protocols are enabled (under the Network Configuration branch in the navigation tree) for the SQL Server instance.

Answer 2

First off, we know that there is no client server communication here. So, based on the error, it isn't permissions or authentication (you have to connect before you can be denied access).

Try the following:

1) Ping - can you get to the server? Run this command in command prompt:

ping servername

If this works, then at least the name is resolving and the client can communicate. If this fails, try the same thing with the server's IP.

2) Telnet - Assuming you don't have a non-standard port (explicitly changed or named instance of SQL Server), run this in command prompt:

telnet servername 1433

If this opens an empty screen, then the client can get to the port. If this fails, try the same command with the IP. If that still fails, you don't have a path to the SQL Server from that machine. You will either need to verify an external firewall or other network connectivity issues.