Researching And Implementation Of VPN Tunnel Technology

There is currently significant interest in the deployment of virtual privatenetworks across IP backbone facilities. VPNs must be implemented through someform of IP tunneling mechanism, where the packet formats and/or the addressingused within the VPN can be unrelated to that used to route the tunneled packetsacross the IP backbone. Such tunnels, depending upon their form, can provide somelevel of intrinsic data security, or this can also be enhanced using other mechanisms(e.g., IPSec). There are numerous IP tunneling mechanisms, including IP/IP, GRE(Generic Routing Encapsulation) tunnels, and L2TP (Layer 2 TunnelingProtocol).Among all the tunnel protocols, L2TP, which is a combination of PPTPand L2F, has became industrial standard. Its designers hope that L2TP will representthe best features of PPTP and L2F. L2TP is a network protocol that encapsulateslayer 2 frames to be sent over IP, X.25, Frame Relay, or Asynchronous TransferMode (ATM) networks. When configured to use IP as its datagram transport, L2TPcan be used as a tunneling protocol over the Internet. L2TP can also be used directlyover various WAN media(such as Frame Relay) without an IP transport layer.During recent period, we have developed a series of L2TP modules for Ningxiapolice office. In this dissertation, we expatiate the feathers of L2TP, and describesome problems which we encountered during development and correspondingsolutions, including some mechanisms for improving efficency of the wholesystem.For example, we introduce upsides mode for predigesting systemcomplication; use common functions for different data structure; adopt two kinds ofmessage format;improve the encryption defect of L2TP, etc. During the period ofimplementation these methods have been proved effectual.