The two versions of Internet Protocol (IP) rely on mechanisms that will convert one protocol to the other and vice versa. Version 4 is still prevalent in the Internet backbone and version 6 in most private networks. In this research we focus on the automatic tunnelling mechanism that provides the encapsulation at one end of the transition tunnel and the de-encapsulation at the other end dependant on the direction of transition. In our research we asked: How secure is the automatic tunnelling mechanism? It is a simple question but important given the number of times transition may occur in any communication and the potential for vulnerabilities. To test the capability of the software instance we launched attacks on the inside and the outside of the tunnel; recorded performance variations and noted opportunities for information sniffing. In all instances the results show weaknesses that can be exploited and the potential for an outsider to not only launch for example DoS attacks but to also disrupt the information being managed in the tunnel. How secure is the automatic tunnelling mechanism?