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When I try to access a named instance of Microsoft SQL server 2008 R2 SP2 on the local network, I have no problem. But when access it outside office from the internet, I can not connect to the database server.

It send back the "famous" following error:

A network-related or instance-specific error occured while establishing a connection to SQL Server. The server was not found or was not accessible. Verify the instance name is correct and that SQL Server is configured to allow remote connections. (provider: SQL Network Interfaces, error: 26 - Error Locating Server/Instance Specified)

This error happen in the winforms application and through the SQL Server Management studio.

The server instance name is correct since I can use it on the same local network. I precised that the server is a domain name such as "\sqldbname". I also make sure to configure SQL Server to allow remote connections from the SSMS > Server Properties > Connections > Remote connections.

More precisions: SQL Browser is up and running. TCP/IP enabled. No problem when installing the database server.

I did a lot of research the last few days and tried everything... I do not have any more ideas.

The system administrator responsible for this server assure me that the ports 1433 and 1434 are open on the database server. I can ping the server from home and when i use putty the command telnet host port I got no error. The command is waiting for me to type something.

Do you have any other ideas that may cause this problem? Port forwarding, etc?

Thank you, LB

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How are you connecting to your office network? Please tell me you're using a VPN connection! – Chris McKeown Aug 7 '12 at 12:17
Named instances do not always run on port 1433. UDP port 1434 is used for port discovery. Are you certain this instance is running on 1433? – James Sneeringer Aug 7 '12 at 12:22
Are you running with Dynamic ports? – KingyCronus Aug 7 '12 at 12:29
@Chris McKeown: Actually I am testing it on a production server for the moment. – LudoB Aug 7 '12 at 12:57
@JamesSneeringer yes, sqlbrowser.exe run on the port 1434. Should I use this parameter instead of 1433? – LudoB Aug 7 '12 at 12:58

We had some weird network issues after applying SQL 2008 R2 SP2.

There is already a Cumulative Update 1 for it that includes 35 hotfixes.

Cumulative update package 1 for SQL Server 2008 R2 Service Pack 2

You may want perform a packet capture as the amount of data to reproduce the issue is quite low and the issue is easily reproducible. The SQL parsers for NetMon are actually quite good.

share|improve this answer
OK, thank you Greg for your input, I will try to apply the update package 1 tomorrow. I downloaded also Microsoft Network Monitor 3.4. Will keep you updated. – LudoB Aug 7 '12 at 14:29
I changed nothing and it's working today according to another tester. I do not really know what happen, I sent an email to the system admin to ask some more clarifications. Will keep you updated if I found out what was causing the error. – LudoB Aug 7 '12 at 23:13

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