v4/v6 Port Address Translation (v4/v6 PAT). This method maps arbitrary pairs of IPv4 addresses and TCP/UDP ports into IPv6 addresses and TCP/UDP ports. It resembles the classical Network Address and Port Translation (NAPT) service currently supported in many LANs to provide Internet access to a number of hosts in a private network by sharing a common public IPv4 address, which is used to address the packets over the public Internet. When a packet is returned to the IPv4 common address, the edge router that supports the NATP service will intercept the packet and replace the common IPv4 destination address with the (private) address of the intended receiver, which is determined by looking up in the NATP table the address of the host associated to the specific destination port carried by the packet. The same technique can be used to map multiple IPv6 addresses into a single IPv4 public address, which allows the forwarding of the datagrams in the IPv4 network and its correct management at IPv4-only hosts. The application of this technique requires low complexity and, indeed, port mapping is an established technique for v4/v6 transition. On the other hand, this approach raises a scalability problem, since the number of IPv6 hosts that can be multiplexed into a single IPv4 address is limited by the number of available TCP/UDP ports (65535). Furthermore, this approach requires that the connection be initiated by the IPv6 nodes in order to create the correct entries in the NATP look-up table. Connections starting from the IPv4 cloud can also be realized, but this requires a more complex architecture, with the local DNS placed within the IPv6 network and statically associated to a public IPv4 address in the NATP translation table.