讨论了虚拟专用网（VPN），尤其是IP-VPN的相关方面。在此基础上分析了IP-VPN的虚拟专用路由网（VPRN）和虚拟专用局域网（VPLS）两种类型。着重讨论了VPRN的两种实现机制——边界网关协议/多协议标记交换（BGP/MPLS）和虚拟路由器（VR），并进行了比较。实现了一种VPLS——虚拟局域网（VLAN）。最后从理论上探讨了基于网络的VPN的服务质量（QoS）并提出了一种VPN QoS的实现途径。

Recently, IP - VPN is proposed as a way satisfying large company´s inter-connect requirement because of the prevalence of Internet. But there are some problems to be solved, especially security and QoS. In this paper, one way of network-based VPN QoS is proposed based on analysis of some available QoS algorithms. For IP - VPN, now there are several mechanisms： VLL, VPRN, VPLS and VPDN. This paper places emphasis on VPRN and VPLS. Two kinds of VPRN: BGP/MPLS and VR are discussed and compared with each other. And besides, VLAN, one way of VPLS, is introduced.