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From Wikipedia, the free encyclopedia

Firewall may refer to:

  • Firewall (construction), a physical barrier inside a building or vehicle, designed to limit the spread of fire, heat and structural collapse
  • Firewall (computing), a technological barrier designed to prevent unauthorized or unwanted communications between sections of a computer network

It may also refer too:

  • Lange (musician), also known as Firewall, the alias of the trance producer
  • Firewall (film), a 2006 thriller film written by Joe Forte, starring Harrison Ford
  • Firewall (novel), a novel by Henning Mankell, featuring Kurt Wallander
  • Firewall (Andy McNab novel), a Nick Stone adventure
  • Firewall, a song by Steve Vai off his Real Illusions: Reflections album
  • Chinese wall, a zone of non-communication between distinct sections of a business, in order to prevent conflicts of interest
  • Great Firewall, China's internet censorship firewall
  • The Alberta Agenda, also known as the Alberta Firewall, a political proposal for the Canadian province
  • An episode of the computer animated series ReBoot titled Firewall.

See also

Simple English

against unauthorised access.]]

Originally, a firewall was a wall that was built to stop (or slow down) the spread of a fire. In terms of computer security, a firewall is a piece of hardware or software. The firewall is there to look at the traffic passing through it. Based on a set of rules, traffic can be allowed, or it can be blocked. A firewall therefore protects one part of the network against unauthorized access.


Different kinds of Firewalls

Packet filtering

Data travels on the internet in small pieces; these are called packets. Each packet has certain metadata attached, like where it is coming from, and where it should be sent to. The easiest thing to do is to look at the metadata. Based on rules, certain packets are then dropped or rejected. All firewalls can do this.

Stateful packet inspection

In addition to the simple packet filtering (above) this kind of firewall also keeps track of connections. A packet can be the start of a new connection, or it can be part of an existing connection. If it is neither of the two, it is probably useless and can be dropped.

Application-layer firewalls

Application-layer firewalls do not just look at the metadata; they also look at the actual data transported. They know how certain protocols work, for example FTP or HTTP. They can then look if the data that is in the packet is valid (for that protocol). If it is not, it can be dropped.

Other things firewalls are used for


Firewalls can provide a secure connection between two networks. This is called tunnelling. The data may be encrypted. It is unencrypted at the other end. Since the firewalls are doing this, the rest of the network is unaware of it. An alternative is to provide a secure access (to the corporate network).

Network address translation

Very often, firewalls can translate IP addresses. That way, many computers can share a few public IP addresses. The firewall translates between the public and the private IP addresses.

Types of firewalls

In general, there are two types of firewalls:

  • Software-based firewalls: these are often run as additional programs on computers that are used for other things. They are often known as personal firewalls
  • Hardware-based firewalls: Hardware based firewalls run on a dedicated computer (or appliance). Often, these offer a better performance than software firewalls, but they are also more expensive.

What firewalls cannot protect against

Firewalls can protect against some problems (viruses and attacks) that come from the internet. They cannot protect against viruses, that come from infected media (like an infected office document on an USB flash drive).

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