Okay, so I am a bit confused on the difference, if any, between the two. GRE's can be encrypted using IPSec and apparently a VPN doesn't necessarily have to be encrypted. So my questions are:
Does a GRE tunnel qualify as a VPN?
How/what is a VPN that isn't encrypted?
Thanks for the help!
I believe that you and some others are looking for some precision of definition in terms that are generally treated loosely and not well defined. I would like to build off the points that Dandy makes: a Virtual Private Network is a network that makes a machine (or a subnet, or a network) that is not physically connected a "virtual" member of some network. In that sense there is no requirement for encryption, and I believe that this is the meaning taken in the wikipedia article. And in that sense then GRE probably does qualify as one kind of VPN.
Another aspect is to observe that a VPN is generally regarded as being a tunnel and that GRE is a tunneling technology. So that would suggest to some people that VPN and GRE are terms that mean the same thing.
But for many people a somewhat more strict meaning is understood when we discuss VPN. To them encryption is a essential ingredient of VPN. And in that sense GRE does not qualify as a VPN since GRE does not provide encryption.
I believe that it gets especially confusing since GRE is so frequently combined with IPSec. And in that sense GRE is very closely related to VPN and could be considered one form of VPN.
While I am known to be one who favors using terms as precisely as possible, I recognize that there is much imprecision in the common usage of the term VPN. I believe that you will need to be clear about the context and the way in which you use the term because there is not any widely accepted precise definition of what constitutes a VPN.