We have our svn server on a machine not accessible from the internet. But we need to be able to check out code from the internet over ssh. Given that we can do port forwarding on a machine accessible from the internet, whats the best way to set this up?

Internet -> A machine on our network - > svn server

            (Port forward here? )        

If not port forwarding, whats the most secure way of doing this, if there is any?