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...a firewall and how does it work

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Question by megan
Submitted on 1/13/2004
Related FAQ: Firewalls FAQ
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what is a firewall and how does it work

Answer by vbspnk
Submitted on 2/20/2004
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how firewall works


Answer by the-mother-of-ideas
Submitted on 4/28/2004
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To answer you question: A firewall is a combination of hardware and software that provides a security system, usually to prevent unauthorized access from outside to an internal network or intranet. A firewall prevents direct communication between network and external computers by routing communication through a proxy server outside of the network. The proxy server determines whether it is safe to let a file pass through to the network. A firewall is also called a security-edge gateway. Hope this helps. ;)


Answer by Abbas
Submitted on 2/6/2005
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GOD Name


Answer by Shirish Mahajan
Submitted on 5/18/2005
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A firewall sits at the junction point or gateway between the two networks, usually a private network and a public network such as the Internet. The earliest firewalls were simply routers

To understand how firewalls work it helps to understand how the different layers of a network interact.

Firewalls operate at different layers to use different criteria to restrict traffic. The lowest layer at which a firewall can work is layer three. In the OSI model this is the network layer. In TCP/IP it is the Internet Protocol layer. This layer is concerned with routing packets to their destination. At this layer a firewall can determine whether a packet is from a trusted source, but cannot be concerned with what it contains or what other packets it is associated with. Firewalls that operate at the transport layer know a little more about a packet, and are able to grant or deny access depending on more sophisticated criteria. At the application level, firewalls know a great deal about what is going on and can be very selective in granting access.


Answer by Arslan Arif
Submitted on 11/5/2006
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All internet communication is accomplished by the exchange of individual "packets" of data. Each packet is transmitted by its source machine toward its destination machine. Packets are the fundamental unit of information flow across the Internet. Even though we refer to "connections" between computers, this "connection" is actually comprised of individual packets travelling between those two "connected" machines. Essentially, they "agree" that they're connected and each machine sends back "acknowledgement packets" to let the sending machine know that the data was received.

In order to reach its destination whether it's another computer two feet away or two continents distant every Internet packet must contain a destination address and port number. And, so that the receiving computer knows who sent the packet, every packet must also contain the IP address and a port number of the originating machine. In other words, any packet travelling the net contains first and foremost its complete source and destination addresses. As we've seen earlier on this site, an IP address always identifies a single machine on the Internet and the port is associated with a particular service or conversation happening on the machine.

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