Feasible address mapping scheme: IPng brings the advantage of a very large address space where even multiple addresses can be easily reserved for each host. In addition to the complex scheme of 128-bit IPv6 address distribution, a simplified method is necessary. To make the transition process easier an optional simple mapping from an old IPv4 address is desirable. Since it is not possible to assume that all IPv4 addresses used are globally unique, the mapping may be site-specific in some cases instead of a fixed prefix.Smart management tools: During the transition and existence of dual protocol networks the demand for a whole set of management tools is clear. The new tools must be clever enough to separate IPv4 and IPv6 characteristics on multiple levels. Detection of different routes and possible translation points must be implemented. A mechanism for checking the IPng capability of remote hosts and devices is essential. Without appropriate management applications the complexity of a dual protocol network will become a nightmare.III. Transition ComponentsHosts: In practice the concept of stepwise transition means that for many years the global Internet contains both hosts restricted to traditional IPv4 operation and hosts equipped with IPv6 capability. To allow seamless interoperation, all hosts running IPng must still be able to communicate with the older technology. On the application level software designed for IPv4 uses the older API while new IPng applications use the new API. Thus the application actually knows which protocol suite it is using. The IPv4 API and standard applications should be available on IPv6 hosts as well if interoperation with common tools (e.g. FTP, Telnet) is expected with older IPv4 hosts.Routers and routing protocols: From the protocol version support point of view of the routers must follow the same rules as individual hosts. New devices with IPng capability cannot assume that all other systems they are interacting with are equipped with the latest protocol support. The compatibility constraint applies to routing protocols as well. While commercial issues gain more and more interest within the Internet infrastructure, IPng routing procedures must allow routing based on traffic source and destination in detail. Especially policy routing and accounting are necessary for funding agencies.Domain Name System: During the transition phase the new IPng capable hosts have both a 32-bit IPv4 address and a 128-bit IPv6 address. Old systems not upgraded yet naturally have an IPv4 address. However, an IPv6 address may already have been assigned to them as well. DNS has to reply with both addresses, if available, for queries from IPng hosts. It is then the decision of the communicating host to select which protocol to use. For old-fashioned queries from IPv4-only hosts the response is the IPv4 address only. A special condition arises when an IPv6 address has been attributed to a specific host in DNS, but the host is not really IPng capable yet. This is called a black hole in the IPng address space and the associated protocol software on communicating hosts must handle such exceptions in an acceptable way.Component Dependencies: The dependencies apply to the order of transition of different network components, the less resistance and delays are faced. DNS servers are the first physical devices to upgrade after a suitable IPng address allocation and mapping scheme is available. This allows new IPv6 hosts to perform name service lookups for IPv6 addresses. Furthermore, the order of migration on host and router software is less critical. The concept of protocol dualism allows IPv4 systems to continue their operation without any modifications. The changes in routing protocols can also be performed with no hurry as the number of IPng capable routers increases.IV. Transition TechniquesDuring the years of transition, we can have three different types of IP nodes, depending on their capabilities, to support different protocols.1. IPv4 only node: A host or router that implements only IPv4. An IPv4-only node does not understand IPv6. The installed base of IPv4 hosts and routers existing before the transition begins are IPv4-only nodes.2. IPv6/IPv4 node: A host or router that implements both IPv4 and IPv6.3. IPv6 node only: A host or router that implements IPv6 and does not implement IPv4. These are not feasible for general purpose Internet use until the transition has proceeded into a phase where most of the communities have upgraded to IPng.For automated protocol compatibility mechanisms like IPv6 in IPv4 encapsulation (tunneling), a special prefix of all zeros has been reserved. This is called an IPv4 compatible address. The rest of the IPv6 address space is reserved for pure IPng addresses, termed IPv6-only addresses. However, direct mapping of IPv4 addresses may still occur using service provider specific prefixes. This is mainly to help the configuration and administration of the address dualism in user organizationsDual IP layer: The most straightforward procedure to satisfy the requirement for full intersystem compatibility is to include a complete IPv4 implementation to new IPv6 systems. This is what we call an IPv6/IPv4 node. They are able to transmit both IPv4 and IPv6 packets and thus interact with all IP systems in the network. When combined with protocol encapsulation, interaction of IPv6 applications will be possible between two IPv6/IPv4 nodes, even if the devices on the route have not yet been upgraded to IPng. The dual stack approach does not necessary imply that the system should contain two separate protocol implementations. It just should act as if it did. From the application point of view there are still two separate APIs and the true decision whether IPv4 or IPv6 is used is made on the application levelAs shown in the below diagram, we have six nodes, out of which A,B,E,F are IPv6 enabled and C,D are IPv4 are enabled.We see, in this diagram the disadvantages of the Dual stack approach, assuming that node A wants to communicate with the node F. Node A creates a IPv6 datagram and transmits it to the next node that is Node B, which is also IPv6 capable. However node B must create an IPv4 datagram to send to node C. Here the data field of the IPv6 packet can be copied into the data field of the IPv4 datagram, and appropriate address mapping can be done.However, in performing the conversion from IPv6 to IPv4, there will be IPv6-specific fields in the