The 15.5 release of SQL Server Data Tools for Visual Studio 2017 is the first release to support SSRS, SSAS, and SSIS in VS 2017. The command line below shows how to install all SSDT components in the only installation of VS 2017 on a machine:
SSDT-Setup-enu.exe /install INSTALLALL /quiet /norestart
To work offline, you’ll need to create a layout folder first (just like in previous versions). Use the /layout parameter and specify the folder path where you want the components to be downloaded:
SSDT-Setup-enu.exe /layout .\offline
The command above would download the components in a folder called offline. The folder will be created if it doesn’t already exist, and the SSDT-Setup-enu executable will be copied into that folder as well.