Restrict What VPN Users Can Get To

166 You can then grant further access on a case-by-case basis. Software engineers will need to get to development servers, for instance. The ideal thing to do in this case would be to set up multiple VPN servers—one for each department—and limit who can use them.

10.4.3 Avoid Public DNS Information for VPN Servers and Routers

Since your VPN server will be an accessible entry point to your network, its better not to let attackers know what it is or what it does. The simplest thing to do is not assign a DNS hostname to your VPN server at all. If you must assign one for internal use, for instance, look into setting up a fake DNS server with meaningless information thats accessible to the greater Internet, while you have a server with specific information to use inside your LAN. [1] At any rate, dont let the outside world see a meaningful name for your VPN server, such as avtunnel.caffeine.net, pptp-gw.caffeine.net, or even win-nt.caffeine.net. Any one of these tells an attacker what type of system it is, and what vulnerabilities can be exploited. Thats why many network administrators will follow some theme, such as Dr. Seuss characters, when naming hosts. Its a good way to give meaningless yet easy to remember names to systems— not just an attempt to be cute. We recommend you set up an alternate DNS server for internal use anyway; this way you can give all servers more meaningful names for Intranet users.

10.5 Keeping Yourself Up-to-Date

Its a good idea to keep your VPN up-to-date, but dont be in a rush to upgrade just because youre looking for a new feature or two. New software is notorious for introducing as many problems as it patches. Here are the primary reasons to upgrade your VPN software: • Theres a security hole in the product you currently use. • Theres a bug that causes system problems such as crashes, memory leaks, or networking problems. • The current version isnt compatible with another product on your network, or a product that the remote users have, and the new version improves interoperability. • The new version has several features essential to the operation of your VPN. Finding information on VPNs is currently like trying to stargaze in the middle of Las Vegas— theres a lot of marketing hype out there, but practical information tends to get washed out. Nonetheless, weve compiled into Appendix B a short list of things to keep up with in the world of VPNs. 1 A discussion of how to set up a fake DNS host can be found in Building Internet Firewalls, by D. Brent Chapman and Elizabeth D. Zwicky OReilly Associates. 167

Chapter 11. A VPN Scenario

If you havent gotten enough of the virtual private network yet, this chapter will cover a real, live, up and running VPN. Weve covered the theory and some general cost-to-benefit analysis, and now we move on to some actual products working in a production environment. Though we have used specific products here like Ascend and Cisco, you may well find that other solutions better fit your enterprise. In other words, this chapter isnt VPN law, just an example.

11.1 The Topology

Well call the company in this case study Immediate PC. It manufactures and sells computer parts and peripherals. About a year ago, Immediate PC made the commitment to standardize its network communications between its various sites over the Internet. Naturally, their main concerns were security, cost, and reliability. Communication needs at Immediate PC are like those at most companies. Sales agents in the field must communicate with manufacturing managers at the factories to order and ensure production of needed stock. The retail store arm of the company also communicates with shipping, manufacturing, and several other departments on a daily basis. Various factories and other divisions across the country must send and obtain data to keep their operations flowing. Several different platforms are used at various levels of the organization. The main corporate network is comprised of Windows NT servers and Windows NT or Windows 95 workstations. Additionally, there are several Unix servers of various flavors. Remote access users employ a variety of operating systems, and a few departments within the main corporate networks use Macintosh systems. Without the Internet, the flow of data and the cost associated with private lines and dial-up access were crippling operations and eating into profits. Having decided to use advanced technology to remedy the situation, Immediate PC migrated gradually from private lines and remote access to a controlled use of the Internet. Research, training, and various levels of approval preceded the move to virtual private networks. After this move, the company reduced the cost of network communication and resolved several communications problems. What emerged was the virtual private network detailed in the network diagram at the end of this chapter. The chosen architecture links a central corporate office with various remote offices, large and small, in addition to a gaggle of remote access users. The following sections detail what was needed in connections to the Internet, equipment, software, and virtual private network solutions.

11.2 Central Office

The central office is the natural source of information about products and operations. Security is critical. Besides the VPN, several other Internet services are centralized here, including the