This worked for me:
Open terminal. Navigate to Eclipse folder.
sudo nano eclipse.ini
at the bottom, add this line in:
-Djava.net.preferIPv4Stack = true
Then ctrl+O to save, ctrl+X to close (it says at bottom). IPv4/IPv6 problems? Solved.
Then delete the cache VonC said to:
<eclipse>/p2/org.eclipse.equinox.p2.repository/cache
(This can be done using "sudo rmdir /p2/org.eclipse.equinox.p2.repository/cache" or by typing "sudo nautilus" into terminal, to open a root-priveleged filesystem browser, than navigating to, selecting the folder, and pressing the delete key). Then restart eclipse, goto Help>install new software>available software sites
Make sure the repos you want (such as "http://download.eclipse.org/egit/updates/") has a "/" right at the end. If it doesn't, delete that entry, and create a new, identical one which does, because Eclipse won't just let you edit it and click ok. Then click ok, and from the combo box choose e.g. the egit link, and lo, it will find it.
Still not working? Window>show view>internal web browser; check it can access internet. Hope that helps!
Credit to:
http://drfits.com/2011/11/13/eclipse-contacting-software-sites-has-encountered-a-problem/
VonC Sep 14 '11 at 6:03
Can you connect to internet at all through Eclipse?
- Open the internal webbrowser. In Eclipse: Window -> show view -> Other -> General: Internal web browser.
- Look up any normal adress, is it working?
Can you connect to another update site? Try for example Eclipse Emma:
http://update.eclemma.org/
Do you see anything there?
What are your proxy preferences? Go to Window -> preferences -> General: Network connections.
The active provider:
Specifies the settings profile to be used when opening connections. Choosing the Direct provider causes all the connections to be opened without the use of a proxy server. Selecting Manual causes settings defined in Eclipse to be used. On some platforms there is also a Native provider available, selecting this one causes settings that were discovered in the OS to be used.
If internet is working fine outside of Eclipse, try changing to Native. After that, try Direct.
I have encountered problems where an update site would not load, then I had to remove it and add it again. This forces Eclipse to reread the contents of the site even if it has a cached copy. So, if you still get no connection to the indigo update site, but everything else is working, try that. Go to Window -> Preferences -> Install/update: Available Software sites. Then remove and add the indigo site. Just remember to copy the adress so you can add it again.
As suggested in a comment below by @lostiniceland, this is a simpler way to achieve the above:
Goto Window -> Preferences -> Install Update -> Available Software Sites => select the entry and click the "Reload" button to the right. This is sometimes also helpful when you have a local updatesite for testing custom plugins
Best Answer
Starting Eclipse with -vmargs -Djava.net.preferIPv4Stack=true works for me