Abstract. In our previous work, we have proposed a new VPN architecture for enabling user-based multiply associated VPNs [1]. Almost all existing VPN technologies assume that users never simultaneously access more than a single VPN. Thus, for realizing a new VPN service allowing users to simultaneously join multiple VPNs, several fundamental mechanisms, such as dynamically changing user’s VPN association status according to the user’s request and authorizing user’s access to a group of VPNs, are required. In this paper, we propose a layered VPN architecture for realizing user-based multiply associated VPN. Our layered VPN architecture consists of three network levels such as PNL (Physical Network Level), LNL (Logical Network Level), and UNL (User Network Level). First, we discuss and classify functions required for each network level. We then present several approaches for implementing each network level using existing layer 2, 3, and 4 networking technologies, and quantitatively...