This memo proposes two new RADIUS attributes with each to carry an Internal Port number and a Configured External Port number, both are associated with a specific NAT device and a specific user, and are configured on a RADIUS server such that when the user requests an Internet connection, the port mapping information can be conveyed to NAS that co-locates with the NAT device via RADIUS protocol, and is used during the NAT operation for IP flows to and from that user. The two attributes also include an IPv4 address or IPv6 address, respectively, as the pinhole internal IP address at the NAT device.