14.8.1 Firewalls

Learn the basics behind firewalls.

There are two types of firewalls: hardware and software. There are three types of firewalls: packet filtering, circuit layer, and application level.

• scan packet, read source and destination
• filters based on TCP/UDP transmission
• monitors the contents of the packet itself

Hardware Firewalls

Hardware firewalls are physical devices that are either standalone and can be connected to a network via a cable or built into another device, like a router. Hardware firewalls are often called network-based firewalls. They act as a gatekeeper that monitor both incoming and outgoing traffic. Usually it can be configured to only allow certain traffic through depending on the origin network or segment, but this feature often costs more to implement.

Software Firewalls

Software firewalls usually handle traffic on the client side. They're installed on hosts so that the firewall manages and filters it's own outgoing traffic (triggered by the end user). They're also called host-based firewalls. Not as robust, but much cheaper and easier to implement.

Microsoft-Windows has it's own host-based firewall built into it's operating system by default. It allows allowing and blocking of ports, protocols, and programs.

Firewall Placement

It's recommended to place firewalls in multiple places in your network, to prevent both outside attacks from spreading in the network and to prevent attacks that start from inside the network.

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