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firewall Last modified: Thursday, August 26, 2004
(fīr´wâl) (n.) A system designed to prevent unauthorized access to or from a private network. Firewalls can be implemented in both hardware and software, or a combination of both. Firewalls are frequently used to prevent unauthorized Internet users from accessing private networks connected to the Internet, especially intranets. All messages entering or leaving the intranet pass through the firewall, which examines each message and blocks those that do not meet the specified security criteria. There are several types of firewall techniques: Packet filter: Looks at each packet entering or leaving the network and accepts or rejects it based on user-defined rules. Packet filtering is fairly effective and transparent to users, but it is difficult to configure. In addition, it is susceptible to IP spoofing. Application gateway: Applies security mechanisms to specific applications, such as FTP and Telnet servers. This is very effective, but can impose a performance degradation. Circuit-level gateway: Applies security mechanisms when a TCP or UDP connection is established. Once the connection has been made, packets can flow between the hosts without further checking. Proxy server: Intercepts all messages entering and leaving the network. The proxy server effectively hides the true network addresses. In practice, many firewalls use two or more of these techniques in concert. A firewall is considered a first line of defense in protecting private information. For greater security, data can be encrypted.
eSecurity Planet  A resource for daily information on e-security targeted to IT managers. The site provides users with information from a variety of sources, including experts at security product and services firms, and the consultants who follow the security industry. Design the Firewall System A practice from the CERT Security Improvement Modules. Extinguishing Firewall Hyperbole Are new firewall technologies improvements or complications? Evaluate the pros and cons. Great Walls of Fire Hackers, lurking cyber punks and viruses. Enough to give any network administrator the willies. But, an efficient firewall could be just the armor your network may need to combat most of these threats.(2001) SecurityTracker.com Information on the latest security vulnerabilities, free SecurityTracker Alerts, and customized vulnerability notification services. Why You Need a Firewall Describes security issues when connecting to the Internet, with information on how to protect your network. This page is hosted by Cisco Systems Inc. Yahoo!'s firewall companies page Yahoo!'s directory of firewall companies. Yahoo!'s firewalls page Yahoo!'s directory of firewalls. Firewall Info Protect your system with a firewall. You must protect your system with a personal firewall, especially if you are using DSL or cable modem. Firewalls FAQ Contains answers to basic questions about firewalls. What Keeps Computers Safe Here's the scoop on the differences between hardware and software firewalls, virus protection, and why you need them.	Related Categories Business Computing Networks Security Related Terms application gateway bastion host bit bucket DMZ extranet firewalking intranet IP spoofing NAT network packet filtering PIX Firewall port scanning proxy server pulsing zombie security stateful inspection TCB zombie