There has been a lot of discussion lately about how MPLS, or network-based VPNs, are replacing other services like Frame Relay and ATM.  What often is missing is an understanding that there are various types of VPNs to accomplish various goals - intentionally.  In this podcast, we take a brief look at some of the various types of VPNs that are present in the market today.  We also consider some of the underlying technologies that make the VPN a VPN, and how and why they are different.  A campanion podcast on "Following the Data" can be heard here.