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Firewalls are systems implemented with software or hardware to protect for example a company's internal network against attacks from the external network. Basic requirements for a firewall are that all network traffic between the internal and external network is channelled through it and that the firewall allows only desired traffic. The firewall itself must also be immune to network attacks. This means among other things that the firewall must be based on a secure operating system.

The firewall defines one checkpoint for network traffic. This checkpoint keeps unauthorised users out of the protected internal network and prevents the use of possibly vulnerable services from the external network. Also communication from the internal network to the external network can be restricted. Firewalls can also be used to improve the security level of the internal network, for instance, by separating various network segments from each other. In addition to attacks against services, the firewall also prevents many kinds of spoofing attacks.

The firewall also provides a possibility to control the network security transactions. For instance, log information and alerts can be implemented within a firewall. A firewall also provides a good platform for other services, such as NAT (Network Address Translation), VPN (Virtual Private Network) and IDS (Intrusion Detection System).

Firewalls, however, do not protect from all attacks. An attacker may use vulnerabilities in the service allowed by the firewall (for example web server). Neither does a firewall protect against attacks where the firewall is overridden or passed. An example of this kind of attack is the abuse of a badly implemented modem pool; nor does a firewall prevent malicious software, such as viruses, from moving between the external and internal networks.

permalink [Permalink] - Updated: Monday, April 24, 2006

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