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First published: 03rd August 2017

Traditionally, a firewall is a control point for network connections. It divides the network 'world' into the inside and the outside. The assumption is that 'outside' contains the 'bad guys' that should be prevented from accessing the systems inside.

Some major types of firewall are:

Packet Filtering

The simplest type of firewall technology - packets are permitted or denied on the basis of their source and destination. Can provide adaquate security in simple situations.

Application-Level Gateways

Proxy severs that come between the client and server, preventing them from exploiting each other's weaknesses.

Statefull Inspection

A much more complex technology that examines the communications at all layers of the OSI model and in relation to past communications and state information derrived from other applications.

Content Vector Protocol

Content Vector Protocol (CVP) is a standard to allow a firewall to communicate with a content scanner (typically, anti-virus software). When a connection is made to transfer a file (usually by HTTP, FTP or SMTP) the firewall keeps the file data and uses CVP to send it to the content scanner. Only when the content scanner replies that the file is permitted (i.e., free from viruses etc.) does the firewall transmit the file to the destination.

Personal Firewall

Firewalls were originally a barrier between an organisation's network and the world, but today many home users and Small/Medium Enterprises are getting online. The trusted network is, very often, just their own machine. A personal firewall is designed for these users and is software that controls the network connections on a single machine. They are usually designed to be very easy to configure and understand.

Distributed Firewall

Larger organisations are finding that the world is not as simple as Inside/Outside. There may be employees attempting unauthorised access within the corporate access. There are probably travelling employees who connect via untrusted ISPs but still need protection and access to corporate data. Also, worms like Nimda have proved troublesome for many large networks with few internal controls.

Personal Firewall-like protection would be usefull in these situations, but controlling the policies across hundreds or thousands of machines would be infeasible. The solution is to use a distributed firewall, which can be simply defined as a Personal Firewall with strong, centralised management. F-Secure Anti-Virus Client Security provides tightly integrated virus protection, personal firewall, intrusion prevention and application control.