Tunneling How VPNs Solve Internet Security Issues

12

1.4 VPN Solutions

A VPN is a conglomerate of useful technologies that originally were assembled by hand. Now the networking companies and ISPs have realized the value of a VPN and are offering products that do the hard work for you. In addition, there is an assortment of free software available on the Internet usually for Unix systems that can be used to create a VPN. In this book, were going to look at some of the commercial and free solutions in detail. Which one you choose for your network will depend on the resources available to you, the platforms you run, your network topology, the time you wish to spend installing and configuring the software, and whether or not you want commercial-level support. We cant cover every vendor and product in this book; they change too quickly. Instead, we offer guidelines you can use on all networks and details on a few stable products that were available when we were writing this edition—we dont mean to imply that theres anything less valuable about competing products. VPN packages range from software solutions that run on or integrate with a network operating system such as the AltaVista Tunnel or CheckPoint Firewall-1 on Windows NT or Unix, to hardware routersfirewalls such as those from Cisco and Ascend, to integrated hardware solutions designed specifically for VPN functions such as VPNet and the Bay Networks Extranet Switch. Some VPN protocols, like SSH or SSL, gained popularity for performing other functions, but have since become used for VPNs as well. In addition to products, ISPs are also offering VPN services to their customers. The tunneling usually takes place on the ISPs equipment. If both ends of the connection are through the same ISP, that ISP might offer a Service Level Agreement SLA guaranteeing a certain maximum amount of latency and uptime.

1.4.1 Quality of Service Issues

Running a virtual private network over the Internet raises an easily forgotten issue of reliability. Lets face it: the Internet isnt always the most reliable network, by nature. Tracing a packet from one point to another, you may pass through a half-dozen different networks of varying speeds, reliability, and utilization—each run by a different company. Any one of these networks could cause problems for a VPN. The lack of reliability of the Internet, and the fact that no one entity controls it, makes troubleshooting VPN problems difficult for a network administrator. If a user cant dial into a remote access server at the corporate headquarters, or theres a problem with a leased line connection, the network administrator knows there are a limited number of possibilities for where the problem may occur: the machine or router on the far end, the telecommunications company providing the link, or the machine or router at the corporate headquarters. For a VPN over the Internet, the problem could be with the machine on the far end, with the ISP on the far end, with one of the networks in between, with the corporate headquarters ISP, or with the machine or router at the corporate headquarters itself. Although a few large ISPs are offering quality of service guarantees with their VPN service if all parties involved are connected to their network, smaller ISPs cant make such a guarantee—and there will always be times when the network administrator is left to her own resources. This book will help you isolate and identify the problem when something goes wrong on your VPN. 13

1.5 A Note on IP Address and Domain Name Conventions Used in This Book

The notation 1.0.0.024 is commonly used in describing IP address ranges. It means start with the address 1.0.0.0 and allow the right-most 8 bits to vary. The 8 is calculated by using 32 bits the maximum for an IP address minus 24 the size specified after the . So 1.0.0.024 means all addresses from 1.0.0.0 to 1.0.0.255. Weve elected to use the same IP address ranges and domain name throughout this book. For Internet-routable IP address ranges, were using the blocks 1.0.0.0-1.255.255.255 or 1.0.0.08 and 2.0.0.0-2.255.255.255 2.0.0.08, which we subnet to suit our needs. These ranges were chosen because they are designated as Internet routable, but are reserved by the IANA and arent currently being used. We hope that using these ranges, rather than randomly picking some or choosing them from active registered networks, will makes examples and figures easier to understand while protecting the innocent. We found that this helped us maintain our own sanity while writing the book. For internal networks, we use the IP ranges set aside in RFC 1918 for use on private networks. These ranges are 10.0.0.0-10.255.255.255 or 10.0.0.08, 172.16.0.0- 172.31.255.255 or 172.16.0.012, and 192.168.0.0-192.168.255.255 or 192.168.0.016. We also subnet these as we deem necessary for an example. The domain name we use for our examples is ora-vpn.com. Within this domain, however, we dont have a hostname convention, because we typically create a hostname to match whatever solution we are writing about in a given chapter.