SERVER\INSTANCE,PORT in ADO.NET connection string

Question

I have my own named instance listening on specific port and I've been using ADO.NET connection strings in the form of IP,PORT or SERVER\INSTANCE. Today I saw something that threw me for a big loop - my app won't connect to a new SQL Server machine using either one form of the connection strings but only IP\INSTANCE,PORT. SQL Server Browser is running. Can someone explain this weirdness? Thanks!

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PT

Answer 1

Providing the port number overrides the named instance name. So if you can connect with IP\INSTANCE,PORT you should also be able to connect to the same instance with IP\NONSENSE,PORT

So you should also be able to connect with IP,PORT which I know you said you could not, but you should double-check that.

As to why you can't connect with IP\INSTANCE when then SQL Server Browser service is running (on the SQL Server computer), I suspect that either UDP port 1434 is not open in the firewall on the SQL Server computer, or the client and server computers are not on the same network subnet. Routers do not normally pass UDP traffic (user datagram protocol) as it is a broadcast message and can cause too much noise on the network.

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Rick Byham, Microsoft, SQL Server Books Online, Implies no warranty