Firewall Research Based On The PPTP Client

VPN developed from special network, establishes private communication channel and provides safely end-to-end data communication. PPTP which is a layer2tunnel protocol of VPN, has been integrated into Windows operating system, and has high security, low cost, highly mobility and wide application prospects in business, military and education etc. Focus on safety consideration, after establishment of PPTP connection, all the packets sent to network by the client would be sent to VPN server first, even packets not accessing to enterprise resources. That increases packets transmission delay on average.Based on the phenomenon, a thought filtering PPTP datagram by TDI filter drivers was put forward, which judged the destination of packet by extracting the internal destination of IP in PPTP packet to selectively encapsulate packet in PPTP and finally made the packet not accessing to enterprise resources directly send to external server. The main work is as follows:1、The mechanism of PPTP encapsulation is analyzed. The intercept technology of the user mode and kernel mode under Windows are explained in detail, whose principle and Intercept position about PPTP packet are given to show that TDI filter drivers can more effectively deal with PPTP packet.2、The key technologies of firewall and related technology about driver development are described. The key modules are given, including TDI filter drivers module, filtering rules module, selective encapsulation module.3、Based on the Windows platform, PPTP-VPN is set up. In the use of SkyNetFireWall, TDI filter drivers which can extract internal destination of IP in PPTP is verified. Security analysis of improved PPTP client, the defects of TDI filter drivers itself and the next research works are given.