Nexus 4 is not sharing internet connection (tethering), while WiFi or Bluetooth connection is successfully established I'm trying to make my nexus 4 sharing its internet connection with other devices.

First I've tried with the portable hotspot: when it is ready I try to connect my nexus 7 2. It connects without problem to the WiFi Net but the WiFi indicators never gets blue and I'm not able to surf.
Then I've tried the bluetooth way: paired the devices and (on the tablet) checked the internet access option. This time the bluetooth indicator gets blue but whenever I try to load a page the browser loads forever.

The same happens with a macbook.

I think that for some unknown reason my phone is setting up a WiFi Net but it doesn't share its internet connection.

How can I make my Nexus 4 share its internet connection?

My Nexus 4 is running Android 4.3, as does the Nexus 7 2
Following @Shadow's suggestion I've googled a bit more...turns out that Android >= 4.1.2 prevents you from using tethering if you are served by a virtual operator (as I am).

This is a nice post http://albertomilone.com/wordpress/?p=581 explains pretty well the situation and propose a solution based on iptables.

EDIT

Looks like this problem is solved with Android 4.4.2 as stated here