| With the quick development of the internet technique, the address of IPv4 will be in the danger of being used up between the year 2005 and 2015.So the IETF develope a new edition of the IP protocol--IPv6, which modernize the IPv4 designed in the 1970s.It's anticipated that with the increasement of the Internet and the requirement of the resolvement of the plug and play, the IPv6 will be used more widely and will replace the IPv4 in the future. The period of transition from IPv4 to IPv6 will be long during which the coexistence and the communication between them is necessary. During the period a strong and flexible transition and coexistence scheme from IPv4 to IPv6 is necessary, too. In addition, the technique to realize the communication between each other should be "seamless" to users and make the transfer of information more efficient. So the mutual operation between IPv4 and IPv6 and the even smooth upgradement scheme must be realized.There are many techniques to realize the translation from IPv4 to IPv6 but localization still exists. They can be parted into these classes as follow according to the principle to realize it:1. Double Stack(RFC 2893 obsolete RFC 1933):The node adopting the technique runs both IPv4 and IPv6 protocol stacks. The shortcoming is that because it still use the IPv4 address, it will not resolve the question of IP address being used up.2 Tunneling (RFC 2893):It allows you to encapsulate one packet head into the other and one protocol will communicate with others through the encapsulation in the other protocol. The shortcoming is that the communication between IPv4 and IPv6 is not resolved.3 NAT-PT(RFC 2766):It's applicable in the communication between the pure IPv4 node and pure IPv6 node. Beside the translation of the address the protocol should be translated too.Compared with each other, in order to realize the communication between IPv4 node and IPv6 node the best method is using the NAT-PT.In the paper I mainly study and resolve the question of the communication between the hosts in the IPv4 net and the hosts in the IPv6 net during the transition period, which is also the deep study of the protocol gateway which is the bridge to connect the IPv4 net and the IPv6 net. In order to better the transition capability, the packet head of IPv6 has much changed compared to that of IPv4: compared to IPv6,six fields of the packet head of IPv4 is deleted, the name and some functions of three fields are changed and two fields are added. So while realizing the communication between the IPv4 net and IPv6 net we must resolve both the transition of the address and the protocol. This text only discuss the experiment system and the steps based on NAT-PT.In the method, it supplies a transparent gateway to realize the communication between the hosts in the IPv4 net and the IPv4 net. The method is realized through the combination of the transition of the address and the protocol. NAT-PT is the boundary gateway between the IPv6 network and IPv4 network. Usually it is a computer on which both IPv4 and IPv6 protocols are running and at least one interface linked to the IPv4 netwok and the other linked to the IPv6 network. NAT-PT can be realized on router or many other computer plantiform such as Linux or FreeBSD or Windows. Cisco has realized NAT-PT on some of its router models. Microsoft IPv6 protocol stack with the transmition function of protocol is the application of NAT-PT.The sort of NAT-PT as following:1. Traditional-NAT-PT model: Traditional-NAT-PT model only resolve the access from the pure IPv6 to IPv4, in which model the active communicator can only be the host in IPv6 field. It can also be parted into basic model and NAPT-PT. As to the basic NAT-PT model, we should obligate an address pool for the IPv6 hosts. Every IPv6 address has a corresponding IPv4 address in the pool.As to the NPAT-PT model it expands the form of one-step transform. It can mutiplex many IPv6 addresses to only one IPv4 address. The material realization is similar o the NAPT in common I...
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