Adelphia web hosting - 4 4 1.2 Transition from IPv4-Only Internet to
4 4 1.2 Transition from IPv4-Only Internet to IPv4/v6 Dual Stack Internet Today, most of the nodes on the Internet use IPv4. We will need to gradually introduce IPv6 to the Internet and hopefully make all nodes on the Internet IPv6-capable. To do this, the IETF has carefully designed IPv6 migration to be seamless. This is achieved by the following two key technologies: Dual stack Tunneling With these technologies, we can transition to IPv6 even though IPv4 and IPv6 are not compatible (IPv4-only devices and IPv6-only devices cannot talk with each other directly). We will go into the details soon. It is expected that we will have a long period of IPv4/v6 dual stack Internet, due to the wide deployment of IPv4 devices. For instance, some of the existing devices, such as IPv4-capable game machines, may not be able to be upgraded to IPv6. Therefore, in this book, we would like to focus on the issues regarding the transi tion from IPv4-only Internet to IPv4/v6 dual stack Internet and the changes in socket API programming. 1.2.1 Dual stack At least in the early stage of IPv6 deployment, IPv6-capable nodes are assumed to be IPv4-capable. They are called IPv4/v6 dual stack nodes or dual stack nodes. Dual stack nodes will use IPv4 to communicate with IPv4 nodes, and use IPv6 to communicate with IPv6 nodes. It is just like a bilingual person he or she will use English when talking to people in the States, and will use Japanese when talking to Japanese people. The determination of protocol version is automatic, based on available DNS records. Because this is based on DNS, and normal users would use fully qualified domain name (FQDN) in email addresses and URLs, the transition from IPv4 to IPv6 is invisible to normal users. For instance, assume that we have a dual stack node, and we are to access http://www.example.com/. A dual stack node will behave as follows: If www.example.com resolves to an IPv4 address, connect to the IPv4 address. In such a case, the DNS database record for www.example.com will be as follows:
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