LinuxGazette: Implementing a Bridging Firewall

What is the difference between a bridging firewall and
a conventional firewall? Usually a firewall also acts as a router:
systems on the inside are configured to see the firewall as a
gateway to the network outside, and routers outside are configured
to see the firewall as the gateway to the protected network. A
bridge is piece of equipment that connects two (or more) network
segments together and passes packets back and forth without the
rest of the network being aware of its existence. In other words, a
router connects two networks together and translates between them;
a bridge is like a patch cable, connecting two portions of one
network together. A bridging firewall acts as a bridge but also
filters the packets it passes, while remaining unseen by either

Why might you want to so such a thing? A couple of reasons
spring to mind:

  • You can plug in a firewall without changing any of your
    existing network software configuration.
  • You may want to protect part of a network where you do not have
    control of the external routing into your network.


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