The term “Firewall” is interpreted very differently. We want to define at this point the meaning of “Firewall” within the boundaries of this reference manual.
A Firewall is a compilation of components, which monitors at a central place the data exchange between two networks. Mostly the Firewall monitors the data exchange between an internal, local network (LAN), and an external network like the Internet.
The Firewall can consist of hard and/or software components:
- In pure hardware systems the Firewall software often runs on a proprietary operating system.
- The Firewall software can also run on a conventional workstation, which is dedicated to this task under Linux, Unix or Windows.
- As a third and frequently used alternative, the Firewall software runs directly within the router, which connects the LAN to the Internet.
In the following sections we only look at the Firewall in a router.
Note: The functions “Intrusion Detection” and “DoS protection“
are part of the content of a Firewall in some applications. The LANCOM
contains these functions also, but they are realised as separate modules
beside the Firewall. Further information can be found in the section
and .