It is difficult to promote the use of existing methods of DDoS attack source trace-back. Source IP address forgery is an important technology that DDoS attackers commonly use. Combined with the characteristics of the datagram and the traditional virtual circuit, orientable complete path (OCP) is put forward. OCP can be used to solve the problem of source IP address forgery, to track attack source, including DDoS attack source, to transmit network data and support dynamic routing. Theoretical analysis has shown the satisfactory results.