And the "How to control network license access using an options file" from Autodesk.
I still have two questions.
First is, if I create a HOST_GROUP, how many hosts I can include?
The second is, after including all my hosts, how I protect my licences a John Doe that knows I'm running a license server. Can I, after allowing all the HOST_GROUPs allowed block access to the license to everybody else?
Yes. Using an INCLUDE option for a host group will only allow those hosts and everyone else not included will be excluded by result. See my options file link in my signature for everything you need to know.