Chapter 4. Building and Maintaining a Secure Network
The concepts of defense-in-depth and layered security best represent the idea of building and maintaining a secure network. It would be great if users could rely on one type of technology or a single device to provide all of our security but that's not realistic, as history proves there are no silver security bullets. Some professionals use the analogy that security is like an onion – it has layers. Alone, each layer is weak and translucent, but together they're tough and solid.
A firewall is one layer but not necessarily the first layer. Figure 4.1 shows examples of different layers. The packet-filtering router that connects your company to the Internet may be the first layer, or there could ...

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