Why does .NET Framework prerequisite not run from same location of my setup file?

I have created a setup project in c# and i had choose dot net framework 3.5 as it's prerequisites and i set the option "Download from the same location as my application". But while it assumed to be run from local when i run the Setup.msi it goes through the 开发者_JS百科internet to install the .NET Framework 3.5.

Could anybody please tell me WHY?

From Application Deployment Prerequisites (emphasis added):

... Visual Studio generates a Windows executable program named Setup.exe, also known as a bootstrapper. The bootstrapper is responsible for installing these prerequisites before your application runs.

The msi file is just a windows installer database, and isn't capable of performing bootstrapping actions.