This paper proposes a Dynamic-Configurable NAT (DCNAT) approach to the inbound session problem for private networks behind NAT routers. DCNAT is a port-based NAT scheme that adopts a registration procedure for a host to register a session with a DCNAT router before originating a communication session to a host behind the DCNAT router. With the registration procedure, the DCNAT router can create NAT binding entries dynamically for address: port translation before the inbound session starts. Furthermore the dynamic creation of NAT binding entries makes DCNAT very flexible in supporting inbound accesses to a large number of services opened dynamically by the private nodes behind an NAT router. Although DCNAT requires minor modification to the originating host and the NAT router, it is highly suitable for proxy-based applications, such as web browsing, or instant message delivery.