Study and implement of VPN penetrating NAT based on IPSec protocol

This paper aims to explore how to address the compatibility of IPSec and NAT, by the research based on IPSec and NAT, a VPN system to solve the compatibility VPN of IPSec and NAT is designed and complemented. First studies the NAT and IPSec protocol and the penetration of NAT based on UDP, describes the existing methods to solve the compatibility and their shortcomings, proposes using of UDP encapsulation of IPSec packets ways to improve the way of IPSec through NAT. For the main problems of achievement of IPSec VPN, including: traversing NAT of LAN interconnection, encapsulating of IPSec packets, and programming, ideas and a complete solution are put forwarded, enabling the LAN connection with Internet networking, exchange of visits to free safety. Experiments show that the system´s network traversing and the IPSec data protection meet the needs of practical applications.