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25: WAN Introduction
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One WAN solution becoming more common today is virtual private networks, commonly called VPNs The network part of the term refers to the use of a public network, such as the Internet, to implement the WAN solution The virtual part of the term hides the public network from the internal network components, such as users and services This is similar to using virtual circuits (VCs) to connect remote locations, such as a corporate office, remote access users and SOHOs, branch and regional offices, and business partners, as shown in Figure 25-7 Actually, a VPN is similar to a Frame Relay network; however, a VPN uses a public network for its connectivity and Frame Relay uses a private one The private part of the term specifies that the traffic should remain private not viewable by eavesdroppers in the network This is accomplished using encryption to keep the data confidential Many VPN technologies exist, such as IPSec, Point-to-Point Tunneling Protocol (PPTP), Layer 2 Transport Protocol (L2TP), SSL, and others; however, this chapter
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FIGURE 25-7 Intranet: same company sites Extranet: third-party and business partners Remote access: users and SOHOs
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serves as a quick introduction to VPNs A detailed introduction to VPNs the different types and the technologies they use, how they work, how to configure them on Cisco devices, and how to troubleshoot them is covered extensively in my book The Complete Cisco VPN Configuration Guide with Cisco Press (ISBN: 9781587052040)
Bene ts
VPNs provide four main benefits over setting up a private WAN network, such as those used by Frame Relay, point-to-point circuits, and ATM:
Security
Security is provided through data encryption to protect confidentiality, data integrity checking to validate packets, and authentication to prevent unauthorized access Public networks, such as the Internet, can be used instead of building a private WAN infrastructure, greatly reducing a company s WAN infrastructure cost Inexpensive high-bandwidth connections, such as DSL and cable, can be used to interconnect offices to allow for fast and secure access to corporate resources Companies can easily add large numbers of users and offices without building a significant WAN infrastructure
Cost
Bandwidth
Scalability
VPN Types
VPNs fall under two implementation types:
Site-to-Site Remote Access
The following sections will expand on these types
Site-to-Site
Site-to-Site VPNs, sometimes called LAN-to-LAN or L2L VPNs, connect two locations or sites together, basically extending a classical WAN design Two intermediate devices, commonly called VPN gateways, protect the traffic between the two LANs This type of VPN tunnels packets between the locations: the
25: WAN Introduction
original IP packet from one LAN is encrypted by one gateway, forwarded to the destination gateway, and then decrypted and forwarded to the local LAN at its end to the destination From the real source and destination s perspective, the VPN is virtual they don t even know their traffic is being protected between the two VPN gateways The most common site-to-site protocol used to protect traffic is IPSec Routers are commonly used as the VPN gateway product, though other products can be used, such as firewalls Cisco products that support IPSec L2L VPNs include routers, ASA and PIX security appliances, and the VPN 3000 concentrators Because of scalability features such as dynamic multipoint VPNs (DMVPNs), Cisco routers are the preferred choice for IPSec L2L gateways L2Ls come in two flavors: intranet and extranet An intranet L2L basically connects two offices of the same company together, such as a corporate office and a regional or branch office An extranet is an L2L VPN that connects two different companies together, such as a corporate office and another company that is a business partner Address translation is commonly required here because the two companies might be using the same private address space
Remote Access
Remote access VPNs are an extension of the classic circuit-switching networks, such as POTS and ISDN They securely connect remote users or SOHOs to a corporate or branch office With a remote access VPN, the VPN provides a virtualization process, making it appear that the remote access user or office is physically connected to the corporate office network Common protocols used for remote access VPNs include IPSec, SSL, PPTP, and L2TP Cisco supports all four of these protocols; however, most of the Cisco s development effort is based on IPSec and SSL These are discussed in the next two sections
Easy VPN Cisco s IPSec remote access solution is called Easy VPN Easy VPN is a design approach Cisco took to make it easy to deploy, scale to a large number of users, and centralize policy configurations Easy VPN involves two components:
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