10.4. Layer 2 Firewalls
A relatively new type of firewall has emerged over the last couple of years: Layer 2. Layer 2 firewalls are “invisible”; they sit on the network and watch packets and filter out bad packets, but they are never seen.
The disadvantage to a typical firewall is that it is a destination on the network. A traditional firewall has a public and a private network, so it has addresses that can be attacked. A frustrated intruder, who is unable to bypass the security mechanisms, can attempt to launch a DoS attack against the firewall directly. Many firewalls are set up so that if the firewall application crashes, the server underneath simply becomes a router—directing traffic from the public to the private network. [2]
[2] Thankfully, ...
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