What Is A Firewall?


A firewall (common misspelling include firewall and fire wall) is software running on your computer which checks the network traffic (e.g. you browsing on the net) and permits or denies passage depending on a set of rules. Traffic to and from your computer goes over a number of different channels, these are called ports, for example web traffic goes over port 80.

A firewall uses up to three methods to control the inbound and/or outbound traffic:

  • Stateful inspection – in this case key parts of the packet with a database of trusted data. Information from within the firewall is compared with information coming externally, if the characteristics are similar enough then the data will get through
  • Packet filtering – All web page requests are sent in small packets( small bits of data) these are checked against a set of filters. All packets which do not pass the filter are blocked, the rest is let through
  • Proxy service- information from the internet is retrieved by the firewall then sent to whatever requested it.

Customizing a firewall

A firewall which automatically denied all access to connections to your computer would be useless as you would not be able to connect to anywhere. Generally when a firewall is installed it will automatically deny all but web traffic. But firewalls can be configured which much more granularity than that.

  • IP address – every computer on the internet is assigned a unique identification, this is called an ip address, they have the structure such as 123.345.7.2. This might be important a particular individual is continually attempting to connect to your machine from a distinct ip.
  • Domain name – denying a particular domain name. For example if there is a specific website that you would not want your children to access.
  • Protocols – a protocol is a way that a pc service will talk to another service. For example the web uses a protocol called http. For home users generally there are many protocols which will never be needed
  • Ports – certain applications communicate over specific ports, as stated about web browsing goes over port 80, certain games for example may communicate over different ports, so may need to enable this to place the game otherwise having most ports closed is best.
  • Specific words and phrases – these can be used to disable certain content which may be deemed to be inappropriate