A variety of mechanisms for implementing Virtual Private Network (VPN) utilizing public IP network infrastructure have been proposed in [1,2,3,4] and more may be emerging. This document attempts to identify a set of criteria for evaluating such mechanisms. The criteria could be used by IETF for evaluating a VPN proposal before advancing it to standard track or by VPN Service Providers or enterprise network administrators for choosing which mechanism to use in order to implement their desired VPN networks. The mechanisms this criteria addresses are exclusively for implementing IP based VPNs, as oppose to non-IP based ones, such as Frame Relay based VPNs, etc.