The Virtual Private Network (VPN) Services provide the delivery or exchange of IP version 4 or version 6 packets, subject to dynamic, destination-based routing, over a network of virtual links (tunnels). The user's IP address range is independent of the provider of Access Services. VPN Services can be considered emulated IPv4 or IPv6 (tunneled in IPv4) routed services, as the routing is constrained to the IP tunnels, which act as point-to-point, virtual interfaces, agnostic to the multi-hop nature of the supporting transport network. Implementation examples are Packet-based VPN services (tunnelling over packet-based access), GRE-based VPN (such as L2TP-based VPN and IPSec VPN), and session-based VPN services (SSH-based or SSL-based tunnelling over session-based access).