Hi, I know global variables violate OOP but it would be nice if anyone can suggest me other practice. Currently in my project I keep only connection string in app.config to sql database. There is a table Configuration in the database which holds data like ftp address, login, password and much more. When my application starts I just simply read this data into static class with many properties called configuration and use it in many other classes. I treat this static configuration class as a global variable. This is very useful but I can feel it is not the proper solution. Thank you very much for your suggestions.
A good use would be Extension Method, I love them 
. In your use case all the configurations/connection strings should go in app config file read more about them here.