ODBC and ADO connection to SQL Server: What protocol is used when connecting to \?
If you don't specify the protocol in the connection string, then it will use the protocol specified for the database driver. The protocol order, by default, is Shared Memory, TCP/IP and then Named Pipes. You could also set a default protocol. 

To specify which protocol to use in a connection string, add tcp: before the server name. Examples: tcp:server1\instance1, tcp:server2, tcp:server3,1433

You can use SQL Server Configuration Manager to see the protocol order or regedit to see the default and protocol order.



The regkey is HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\MSSQLServer\Client\SNI11.0 for 64-bit applications and HKEY_LOCAL_MACHINE\SOFTWARE\WOW6432Node\Microsoft\MSSQLServer\Client\SNI11.0 for 32-bit applications.