IPv6 does not allow for fragmentation and reassembly at an intermediate router these operations can be performed only by the source and destination. Selection of a deployment strategy will depend on current network environment, and factors such as the forecast of traffic for IPv6 and availability of IPv6 applications on end systems. It is expected that IPv4 and IPv6 hosts will need to coexist for a substantial time during the steady migration from IPv4 to IPv6, and the development of transition strategies, tools, and mechanisms has been part of the basic IPv6 design from the start. A key part of IPv6 design is its ability to integrate into and coexist with existing IP networks. The success of IPv6 will depend ultimately on the innovative applications that run over IPv6. IPv6 reintroduces end-to-end security that is not always readily available throughout an NAT-based network.
The flexibility of the IPv6 address space provides the support for private addresses but should reduce the use of network address translation (NAT) because global addresses are widely available. The need for an always-on environment to be connectable precludes these IP address conversion, pooling, and temporary allocation techniques, and the “plug and play” required by consumer Internet applications further increases address requirements. Although these techniques appear to increase the address space and satisfy the traditional client/server setup, they fail to meet the requirements of new applications. The lifetime of IPv4 has been extended using techniques such as address reuse with translation and temporary use allocations.
The use of globally unique IPv6 addresses simplifies the mechanisms used for reachability and end-to-end security for network devices, functionally crucial to the applications and services driving the demand for the addresses. The current IP address space is unable to satisfy the potentially large increase in number of users or the geographical needs of Internet expansion, let alone the requirements of emerging applications such as Internet-enabled personal digital assistants (PDAs), personal area networks (PANs), Internet-connected transportation, integrated telephony services, and distributed gaming. IPv6 will allow a return to a global end-to-end environment where the addressing rules of the network are transparent to applications.
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