■ The Building Distribution layer performs filtering to keep unnecessary traffic from theCampus Core. This packet filtering can be considered a security function because it doesprevent some undesired access to other modules. Given that switches in the BuildingDistribution layer are typically multilayer switches (and are therefore Layer 3–aware), this isthe first place on the data path in which filtering based on network layer information can beperformed.■ The Campus Core layer is a high-speed switching backbone and should be designed to switchpackets as quickly as possible; it should not perform any security functions, because doing sowould slow down the switching of packets.■ The Server Farm module’s primary goal is to provide application services to end users anddevices. Enterprises often overlook the Server Farm module from a security perspective.Given the high degree of access that most employees have to these servers, they often becomethe primary goal of internally originated attacks. Simply relying on effective passwords doesnot provide a comprehensive attack mitigation strategy. Using host-based and network-basedIPSs and IDSs, private VLANs, and access control provides a much more comprehensiveattack response. For example, onboard IDS within the Server Farm’s multilayer switchesinspects traffic flows.■ The Server Farm module typically includes network management systems to securely manageall devices and hosts within the enterprise architecture. For example, syslog providesimportant information on security violations and configuration changes by logging securityrelated events (authentication and so on). An authentication, authorization, and accounting(AAA) security server also works with a one-time password (OTP) server to provide a highlevel of security to all local and remote users. AAA and OTP authentication reduces thelikelihood of a successful password attack.IPS and IDSIDSs act like an alarm system in the physical world. When an IDS detects something it considersan attack, it either takes corrective action or notifies a management system so that an administratorcan take action.HIDSs work by intercepting operating system and application calls on an individual host and canalso operate via after-the-fact analysis of local log files. The former approach allows better attackprevention, and the latter approach is a more passive attack-response role.
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