I have a problem that I have been trying to fix over 3 months now, I'm using Ubuntu 12.04 64bit with Windows 7 as a Guest on VirtualBox, I have a USB Modem which doesn't support Linux, the Modem works good on the Guest but I don't know how to let the Host (Ubuntu) use that connection, I have searched around the Internet and most documents and fixes for how to share Host's connection with Guest, not Guest with Host. Beside, I've found some posts with similar problem but I couldn't understand the workarounds, I'm still beginner. So could anyone provide a step-by-step guide how to share Guest's Internet with Host? Thanks a lot!
There is a great answer at this post to create a host only connection for your Virtualbox that can be seen by Ubuntu to be used for connecting into your VM for network connection sharing.
Before you follow those directions you need to create the virtual connection. Copy and paste the following in a terminal window to create it:
vboxmanage hostonlyif create
Also, follow these instructions here after you have created the host only connection and have it configured to setup Internet Connection Sharing in your Windows VM so that you can share your connection.
make the network adapter a 'host-only" adapter ( just click devices menu above the running virtual machine and change the "attached to" network adapter setting to "Host-only" and then you will need to wait a few minutes while the changes propagate and/or you change the hosts network addresses to match the new guests host-only adapter address (192.168.0.1)