Internet Security Systems Inc. IPv6 is a new, widely available version of the Internet Protocol that carries a number of significant performance and security advantages over earlier versions. These same benefits also work to the advantage of IPv6-savvy attackers against, network administrators have not deployed IPv6. IPv4 administrators are unaware that IPv6 is available nearly anywhere IPv4 is available and that IPv6 traffic can pass through their networks without their awareness. Because they have ignored IPv6 as something to worry about in the future, they frequently lack the expertise to manage it and they assume it is not present on their networks. But IPv6 and IPv6 transitional mechanisms offer new security issues and open new avenues of attack even on IPv4 based networks. This presentation will examine the current state of IPv6 and IPv6 transitional mechanisms and their deployment. Some of the security implications against IPv4-only networks in this multiprotocol environment will be explored. Recommendations and best praactices for the secure operation of IPv4-only networks in an IPv6 enabled world as well as IPv4/IPv6 dual stack networks will be offered for the network administrators in these environments. This will be of moderate technical level intended for IPv4 administrators and network security professionals.