Hi Saravanan,
1. According to my analysis, tools.hana.ondemand.com will not list down any missing core eclipse components for installation. In your attached screenshot, it is evident that the components missing in your eclipse tool is a core eclipse component.
2. Get your proxy settings right as mentioned above and try download.eclipse.org/releases/mars, this will list down the core eclipse components along with Add-on components.
Thanks,
Gaurav