How to connect to SQL Server via proxy ?

Question

Suppose I have 2 network layers: network layer A and network layer C, network layer A is the internal network layer without using the internet, network layer C uses the internet, in network layer C I use management software sales with SQL Server connection over the Internet, with following chain connection:

[CODE]

public static string sConnectionString = @ "Server = IP WAN, Port 1433; Database = MyData; User Id = sa; password = xxx";

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The question is, I am at network layer A, intranet layer, how do I want to use sales management software to connect SQL Server via proxy? If I use a proxy connection, how should I fix it?

 [CODE]

public static string sConnectionString = ??? // via proxy ???

 [/CODE]