The SAFE blueprint, "SAFE: A Secure Blueprint for Enterprise Networks," was originally published in 2000. Since then, it has become one of the most downloaded documents that Cisco Systems has ever published. The principle goal of the paper was to provide best-practice information to network architects who needed to consider the security requirements of their networks. Unlike previous works, the SAFE Enterprise blueprint is based on the concepts of modularity within the network, along with "defense in depth." The driving motivators in determining the location of security within the design are the analysis of expected threats and the methods of mitigating those threats. The concept of defense in depth supplies resiliency in the overall security of the network because it provides for a layered approach. The failure of one security system is less likely to lead to the compromise of network resources because the security is applied in layers.
The general design of the SAFE Enterprise blueprint includes three primary layers (shown in Figure 18-1):
The enterprise campus
The enterprise edge
The service provider (SP) edge
The SP edge layer is implemented not by the enterprise but by the Internet service provider (ISP). It is included in the architecture to indicate that specific security features should be requested of an ISP to mitigate certain attacks, but that is beyond the scope of this discussion and of the whitepaper "SAFE: A Security Blueprint for Enterprise Networks."
The second layer of functionality is shown in Figure 18-2. Here the detail of the various modules within each functional area is shown. Each module depicted performs a specific function and has a unique security requirement.
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