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Firewalls 

A firewall can be defined as a system that is designed to prevent unauthorised access to or from a private network. Firewalls checks all the messages and blocks the messages that do not meet the specified security criteria.

Network Firewall The firewall can be thought of as a pair of mechanisms: one which exists to block traffic, and the other which exists to permit traffic. Some firewalls give more importance on blocking traffic while others emphasize on permitting traffic. The firewall implements an access control policy. It's also important to recognize that the firewall's configuration, because it is a mechanism for enforcing policy, imposes its policy on everything behind it. Administrators for firewalls managing the connectivity for a large number of hosts therefore have a heavy responsibility.  Why install a firewall A firewall's purpose is to keep the jerks out of your network while still letting you get your job done.  Many corporations use their firewall systems as a place to store public information about corporate products and services, files to download, bug-fixes, and so forth. Several of these systems have become important parts of the Internet service structure (e.g., UUnet.uu.net, whitehouse.gov, gatekeeper.dec.com) and have reflected well on their organizational sponsors. Note that while this is historically true, most organizations now place public information on a Web server, often protected by a firewall, but not normally on the firewall itself.  Firewall protect from Firewalls cannot protect information against attacks that don't go through the firewall. For a firewall to work, it must be a part of a consistent overall organizational security architecture. Firewall policies must be realistic and reflect the level of security in the entire network. For example, a site with top secret or classified data doesn't need a firewall at all: they shouldn't be hooking up to the Internet in the first place, or the systems with the really secret data should be isolated from the rest of the corporate network.  Firewalls can't protect against tunneling over most application protocols to trojaned or poorly written clients. There are no magic bullets and a firewall is not an excuse to not implement software controls on internal networks or ignore host security on servers. Tunneling ``bad'' things over HTTP, SMTP, and other protocols is quite simple and trivially demonstrated. Security isn't ``fire and forget''.  Lastly, firewalls can't protect against bad things being allowed through them. For instance, many Trojan Horses use the Internet Relay Chat (IRC) protocol to allow an attacker to control a compromised internal host from a public IRC server. If you allow any internal system to connect to any external system, then your firewall will provide no protection from this vector of attack.

Links

SecurityTracker.com
Information on the latest security vulnerabilities, free SecurityTracker Alerts, and customized vulnerability notification services

www.cisco.com
With the rapid growth of interest in the Internet and the Windows NT operating system, network security has become a major concern to companies throughout the world. The fact that the information and tools needed to penetrate the security of corporate networks are widely available has only increased that concern.

www.esecurityplanet.com

The startup employs a policy engine that will help users track applications during the data-recovery process.

Related Topics on Computer and Information security

1. Software Vulnerability Control
2. Firewall Protection
3. Network Intrusion Detection
4. Network Port Scanning
5. Network Tools passwords
6. Types of attacks
7. Application Level Protection
8. Systems Protection
9. Mail and Security
10. Hostile Software

For more topics and tutorials visit - http://www.comptechdoc.org