| With the wide application of Internet and the rapid development of network technology,network hosts grow exponentially. Distributable IPv4 addresses will be soon dried up. So the next generation Internet protocol IPv6 replacing IPv4 is the fundamental approach to solve the problem of insufficient addresses. But IP upgrade is not completed in a short period of time,therefore, IPv4 to IPv6 technology arises at the historic moment. The current IPv4/IPv6 transition technology mainly includes dual stack, tunnel technology and protocol translation technology.In protocol translation technology, the transition scheme based on DNS46 and NAT46 got the attention of many research organizations both at home and abroad. This article carries the thorough research on DNS46 method. Because the IPv6 address space is greater than the IPv4 address space, this research is focused on how to effectively to server IPv6 address dynamically mapping. DNS46 needs to have enough performance processing large-scale concurrent access for the client, so we need to study the high-speed cache lookup algorithm based on domain keyword. Because the synchronization of DNS46 and NAT46 on address mapping affects the performance of the whole 46 transition system, so it is necessary to investigate an efficient DNS46 and NAT46 synchronization mechanism. In this paper, the main work is as follows:First,this paper proposes a dynamic cache address mapping algorithm based on the time factor. Protocol translation uses a pool of given IPv4 addresses to achieve address mapping,and the cache time of address mapping record is determined reasonably by survival time of DNS responses, space utilization of the reserved IPv4 address pool and the current concurrent traffic for effective cache management and the transparent service for the client. It will improve the efficiency of the reuse of the reserved IPv4 address pool.Secondly,the paper puts forward a kind of efficient hash lookup algorithm based on top-level domain level index and insertion sorting on frequency statistics. According to the special domain keyword format this method makes top-level domain name prefix matching as the primary index, and then caches the address mapping records by high-speed hash algorithm.The orderly chain processing is adopted for hash conflicts, and we add the frequency statistics field to each hash node, and do insertion sorting on that field for each hash chain. According to the practical application environment, this method can effectively improve the efficiency of cache lookup.Then, the paper puts forward a scheme of address mapping synchronization mechanism based on the kernel configuration. There are a lot of addition and deletion messages to be exchanged between DNS46 and NAT46 when address mapping is being done. Frequent communication might increase the burden of DNS46 system, which turns to become the performance bottleneck. So in this article, the message communication based on the kernel configuration can solve the problems of heavy communication costs by traditional case which does in user mode. The method is based on Netfilter framework of kernel mode, and constructs IP packets to implement DNS46 and NAT46 synchronization.Finally, according to the above key technologies, DNS46 system was designed and implemented. The system can correctly and efficiently complete the IPv4/IPv6 transition.DNS46 system is fully functional.Through several studies of this paper, we can solve the communication problems of IPv4 clients and IPv6 servers in the IPv4/IPv6 transition period to a certain extent. Favourable foundation has been laid for a large-scale deployment of DNS46 and the popularity of IPv6 protocol implementation of the next generation Internet. It's helpful to promote the positive development of the Internet. |
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