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Printable Version: RFC2196.PDF
RFC 2196 Site Security Handbook September 1997 Proxy servers can also be configured to encrypt data streams based on a variety of parameters. An organization might use this feature to allow encrypted connections between two locations whose sole access points are on the Internet. Firewalls are typically thought of as a way to keep intruders out, but they are also often used as a way to let legitimate users into a site. There are many examples where a valid user might need to regularly access the "home" site while on travel to trade shows and conferences, etc. Access to the Internet is often available but may be through an untrusted machine or network. A correctly configured proxy server can allow the correct users into the site while still denying access to other users. The current best effort in firewall techniques is found using a combination of a pair of screening routers with one or more proxy servers on a network between the two routers. This setup allows the external router to block off any attempts to use the underlying IP layer to break security (IP spoofing, source routing, packet fragments), while allowing the proxy server to handle potential security holes in the higher layer protocols. The internal router's purpose is to block all traffic except to the proxy server. If this setup is rigidly implemented, a high level of security can be achieved. Most firewalls provide logging which can be tuned to make security administration of the network more convenient. Logging may be centralized and the system may be configured to send out alerts for abnormal conditions. It is important to regularly monitor these logs for any signs of intrusions or break-in attempts. Since some intruders will attempt to cover their tracks by editing logs, it is desirable to protect these logs. A variety of methods is available, including: write once, read many (WORM) drives; papers logs; and centralized logging via the "syslog" utility. Another technique is to use a "fake" serial printer, but have the serial port connected to an isolated machine or PC which keeps the logs. Firewalls are available in a wide range of quality and strengths. Commercial packages start at approximately $10,000US and go up to over $250,000US. "Home grown" firewalls can be built for smaller amounts of capital. It should be remembered that the correct setup of a firewall (commercial or homegrown) requires a significant amount of skill and knowledge of TCP/IP. Both types require regular maintenance, installation of software patches and updates, and regular monitoring. When budgeting for a firewall, these additional costs should be considered in addition to the cost of the physical elements of the firewall. Fraser, Ed. Informational [Page 23]