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.
•E-mail this definition to a colleague• Sponsored listings Symantec: Virus Security and Removal - Stop Zotob Virus now. Visit Symantec for updated information and resources. Covad: Firewall Services - Get Fast Internet for Small and Medium Businesses at the Official Covad Site- Now Our Lowest Pricing Ever. Free Install Kit and Router. Citrix® NetScaler® Security Solution - Secure your applications against attack. Download a White Paper now! For internet.com pages about firewall . Also check out the following links! 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. 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. 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. What Keeps Computers Safe Here's the scoop on the differences between hardware and software firewalls, virus protection, and why you need them. 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. Sponsored listings Network IPS with Firewall Architecture from Top Layer - Provides businesses with high-performance network firewall protection against worms, viruses, trojans, DDoS attacks, and Microsoft vulnerabilities. INSA: Firewall Security - Reseller of network security products, including firewalls, intrusion detection and prevention devices, anti-virus appliances, and more. Network Liquidators: Network Firewalls - An online destination for discount used, refurbished, and new open box network equipment. Up to 90% off list price. ISWest: Internet Firewall - Advanced Firewall is designed to provide network-based firewall protection for secure access. Rackspace: Network Security Services - Managed hosting solutions with a comprehensive suite of security technologies. 0% downtime with money-back guarantee. 24x7 live Fanatical Support.	Business Computing Networks Security 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 Give Us Your Feedback Firewalls firewall Products Shop by Top Models: SonicWALL (01-SSC-5700) Pro 2040 Firewall 23 store offers from $1160 - $1870 D-Link NetDefend DFL-700 (DHDFL700) Firewall 18 store offers from $301 - $392 Cisco PIX Firewall 501 (PIX-501-BUN-K9) 20 store offers from $327 - $499 WatchGuard Technologies FireBox X500 (wg40500) Firewall 22 store offers from $1125 - $1989 SonicWALL TZ 170 10 Node (01-ssc-5555) Firewall 23 store offers from $272 - $445