Recuperando el ConnectionString del Web.config

web.config
connectionStrings
add name="CNN" providerName="System.Data.SqlClient" connectionString="SERVER=miserver;Initial Catalog=mibase;User=miusuario;Password=mipassword"
connectionStrings


archivo.cs
string ConnectionString = ConfigurationManager.ConnectionStrings["CNN"].ConnectionString;
string ProviderName = ConfigurationManager.ConnectionStrings["CNN"].ProviderName;