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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.
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.
Information on the latest
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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
startup employs a policy engine that will help users track
applications during the data-recovery process.
Related Topics on Computer and
- Firewall Protection
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- Systems Protection
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- Hostile Software
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