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Download free Secure Configuration of a Cisco 837 ADSL firewall router.pdf This paper describes, hopefully, a fairly typical small office/business scenario and one method to connect it securely to the Internet using a commercially available firewall/router, the Cisco 837 ADSL router. A summary of the relevant security features of the router is provided and a step-by-step explanation of the required configuration to use these features to their maximum-security effect. Finally some results are provided of a before and after scan performed on the network using the security scanning tool nmap. The paper is intended to provide a template and example for current recommended practices. It has become almost essential for business of all sizes to use the Internet to do business. Many businesses see the Internet as a way of increasing sales, working more efficiently or just keeping up with competitors. At the small business end of town this Internet connection tends to be done in hurry with the business just happy to have their Internet connection up and working. Typically not much thought or time is given to the security of the Internet connection. The following paper explains, via example, how to configure a commercially available firewall/router to, as far as possible, securely connect a small business office to the Internet using the most current recommended practices. A common cost effective method of connecting small business to the Internet is via ADSL. ADSL connections require a device at the business office to terminate the ADSL line from the local Telephone Company. This device can be a simple, cheap ADSL modem or more sophisticated ADSL router. Wise businesses will then use some type of Firewall software or equipment to protect the office internal network from potential attack from the Internet. The Firewall could be of the personal type, software installed on the end users workstations, e.g. Zone Alarm or Kerio firewall, dedicated, stand alone firewall installed between the Internet ADSL router/modem and the internal network, e.g. Checkpoint Firewall-1 or Cisco PIX, or a firewall function integrated into the ADSL router/modem. Personal firewalls have an issue that they need careful configuration not to restrict internal office PC-to-PC communications but at the same time stop access from the Internet. Stand-alone firewalls are an additional piece of equipment and cost that needs configuration and maintenance. Integrated firewalls can overcome some of these issues and, after all, if the business needs a device to connect to the Internet plus a firewall, why not buy something that does both.

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