What Is A Firewall
What Is A Firewall
A method for keeping a network secure from intruders. It can be a single router that filters out unwanted packets or may comprise a combination of routers and servers each performing some type of firewall processing.
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.
While much effort has been made excluding unwanted input to the internal network, less attention has been paid to monitoring what goes out. Spyware are applications that keep track of your habits and send those statistics to a Web site.
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. Also 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.
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.
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.
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