Firewall Guide - Compare Firewalls

The original meaning of the word 'firewall' is a wall designed or intended to prevent the spread of fire from one room to another. From a computer-security perspective, the Internet is a flammable, dangerous and volatile environment. In this context "firewall" is an excellent metaphor for network and internet security.

Packet Filtering

All Internet traffic travels in the form of packets. A packet is a limited quantity of data. In packet filtering, only the protocol and the address information of each incoming and outgoing packet is examined, allowing or disallowing their transmission or acceptance on the basis of a set of configurable rules, called policies.

Circuit Level Gateway

The Circuit Level Gateway firewall system validates connections before allowing data to be exchanged. The firewall doesn't just allow or disallow packets but also determines whether there is a valid connection between both ends, as determined by a set of configurable rules.

Application Gateway

This system goes even further in its approach and is usually considered the most secure kind of firewall. The Application Gateway acts as a proxy for applications. All data exchanges with the remote system are performed by the gateway on their behalf. This renders the computers behind the firewall invisible to all but the remote system.

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