计算机网络外文翻译

附录：英文技术资料翻译

英文原文：

Solutions, such as the various encryption methods and PKI, enable businesses to securely extend their networks through the Internet. One way in which businesses accomplish this extension is through Virtual Private Networks (VPNs).

A VPN is a private network that is created via tunneling over a public network, usually the Internet. Instead of using a dedicated physical connection, a VPN uses virtual connections routed through the Internet from the organization to the remote site. The first VPNs were strictly IP tunnels that did not include authentication or encryption of the data. For example, Generic Routing Encapsulation (GRE) is a tunneling protocol developed by Cisco that can encapsulate a wide variety of Network Layer protocol packet types inside IP tunnels. This creates a virtual point-to-point link to Cisco routers at remote points over an IP internetwork. Other examples of VPNs that do not automatically include security measures are Frame Relay, ATM PVCs, and MultIProtocol Label Switching (MPLS) networks.

A VPN is a communications environment in which access is strictly controlled to permit peer connections within a defined community of interest. Confidentiality is achieved by encrypting the traffic within the VPN. Today, a secure implementation of VPN with encryption is what is generally equated with the concept of virtual private networking.

VPNs have many benefits:

Cost savings - VPNs enable organizations to use cost-effective, third-party Internet transport to connect remote offices and remote users to the main corporate site. VPNs eliminate expensive dedicated WAN links and modem banks. Additionally, with the advent of cost-effective, high-bandwidth technologies, such as DSL,

organizations can use VPNs to reduce their connectivity costs while simultaneously increasing remote connection bandwidth.

●Security - VPNs provide the highest level of security by using

advanced encryption and authentication protocols that protect data from unauthorized access.

●Scalability- VPNs enable corporations to use the Internet

infrastructure that is within Internet service providers (ISPs) and devices. This makes it easy to add new users, so that

corporations can add significant capacity without adding significant infrastructure.

●Compatibility with broadband technology- VPNs allow mobile

workers, telecommuters, and people who want to extend their

workday to take advantage of high-speed, broadband connectivity to gain access to their corporate networks, providing workers significant flexibility and efficiency. High-speed broadband connections provide a cost-effective solution for connecting remote offices.

In the simplest sense, a VPN connects two endpoints over a public network to form a logical connection. The logical connections can be made at either Layer 2 or Layer 3 of the OSI model. VPN technologies can be classified broadly on these logical connection models as Layer 2 VPNs or Layer 3 VPNs. Establishing connectivity between sites over a Layer 2 or Layer 3 VPN is the same. A delivery header is added in front of the payload to get it to the destination site. This chapter focuses on Layer 3 VPN technology.

Common examples of Layer 3 VPNs are GRE, MPLS, and IPSec. Layer 3 VPNs can be point-to-point site connections such as GRE and IPSec, or they can establish any-to-any connectivity to many sites using MPLS.

Generic routing encapsulation (GRE) was originally developed by Cisco and later standardized as RFC 1701. An IP delivery header for GRE is defined in RFC 1702. A GRE tunnel between two sites that have IP