Building connect strings in the Synergy/DE online documentation describes the basic syntax for SQL OpenNet network strings for SQL Connection. This article describes how to use a second network string for a multi-tier connection—i.e., a connection that uses a "middle" machine as a gateway (e.g., a firewall), as illustrated in the diagram at the end of this article.

To use a second network string, add it after the first network string (which begins with @), and start the second network string with two “at” signs (@@). Here’s the basic syntax (see Building connect strings for information on database_info and opennet_info):

net:database_info@opennet_info@@opennet_info

Additionally, in the first network string (@opennet_info), set the driver to VTX3—for example: @MyFirstServer!VTX3. In the second network string (@@opennet_info), specify the driver for the database—for example: @@MySecondServer!VTX12_ODBC.

SQL Connection connects first to the SQL OpenNet service on the server specified in the first network string. From there it connects to the SQL OpenNet service on the server specified in the second network string. The database_info string is used on the second server, as illustrated in the following diagram: