The Hype Cycles for Consumer Technologies announced that the level of "Slope of Enlightenment" was achieved by Voice over Internet Protocol (VoIP) in 2007. This stable growth rate expects that the level of "Plateau of productivity" will be achieved in the forthcoming years. While marching towards the exponential growth by balancing other promoting technologies, security becomes the pressing factor. VoIP should not compromise for security which may depreciate its growth rate. Since the rate of the users using VoIP services increases more than the expected, it is vulnerable to all types of attacks that Internet is now facing. The approach proposed includes a new framework, with which the Distributed Denial of Service (DDoS) attacks generated by a reflector attack using a spoofed IP address and impersonation in the VoIP networks can be detected and prevented. MAC based routing table, maintained by the server, can detect the DDoS attacks generated by a reflector attack. MD5 and RSA were used to generate the certificates for the legitimate users. This generated certificate and the routing table enable this approach to rightly detect DDoS attacks and to generate a block list of IP addresses. The next time, when there is a connection establishment request from the block listed IP address, the request will be denied. Hence, the network can be protected from being attacked in the initial phase itself. The experimental setup and the NS-2 simulation results support the method.