Firewall
The primary method for keeping a computer secure from intruders. A firewall allows or blocks traffic into and out of a private network or the user’s computer. Firewalls are widely used to give users secure access to the Internet as well as to separate a company’s public Web server from its internal network. Firewalls are also used to keep internal network segments secure; for example, the accounting network might be vulnerable to snooping from within the enterprise.
In the home, a personal firewall typically comes with or is installed in the user’s computer. Personal firewalls may also detect outbound traffic to guard against spyware, which could be sending your surfing habits to a Web site. They alert you when software makes an outbound request for the first time
In the organization, a firewall can be a stand-alone machine or software in a router or server. It can be as simple as a single router that filters out unwanted packets, or it may comprise a combination of routers and servers each performing some type of firewall processing.
Firewall Techniques
Following are the different methods used to provide firewall protection, and several of them are often used in combination.
Stateful Inspection
Tracks the transaction to ensure that inbound packets were requested by the user. Generally can examine multiple layers of the protocol stack, including the data, if required, so blocking can be made at any layer or depth.
Network Address Translation (NAT)
Allows one IP address, which is shown to the outside world, to refer to many IP addresses internally; one on each client station. Performs the translation back and forth. NAT is found in routers and is built into Windows Internet Connection Sharing (ICS)
Packet Filter
Blocks traffic based on a specific Web address (IP address) or type of application (e-mail, ftp, Web, etc.), which is specified by port number. Packet filtering is typically done in a router, which is known as a “screening router.
Proxy Server
Serves as a relay between two networks, breaking the connection between the two. Also typically caches Web pages (see proxy server).
Corporate website hosting said,
October 31, 2006 @ 2:33 pm
A firewall is a device that guards the entrance to a private network and keeps out unauthorized or unwanted traffic. Firewalls are usually placed between the users of a LAN and the Internet and can cache previously visited sites to avoid excessive use of bandwidth. It also logs attempted intrusions. Firewalls maintain a level of segregation between two networks while permitting the requisite level of connectivity.