The design and implementation of NAPT function in border gateway based on LKM

A function of Network Address Port Translation (NAPT) is designed and implemented based on Loadable Kernel Modules (LKM) for boarder gateway to meet the require of processing efficiency and performance in scene of the space-air-ground integrated network. In this paper, the NAPT is designed to be a LKM in border gateway for excellent flexibility, extensibility and maintainability. And it is loaded into the Network Layer to achieve its functions by using Netfilter subsystem in Linux kernel. The framework, algorithm, flow chart, and key data structure are given. The experimental results show that the gateway successfully implements NAPT function and have excellent processing efficiency and performance: The throughput achieves over 94Mbits/s data transmission rate on 100M-Ethernet network-card. Moreover, the NAPT processing delay in gateway is about 0.010ms. And, when the sending rate of Jperf is set to 100Mbits/s, the Round Trip Transfer time (RTT) of TCP is about 1.60ms.