Local Area Networks (LANs) in Aircraft - FTP Directory Listing - FAA

in-depth manner. Defense-in-depth means that redundant protection systems are deployed so
that if one or more protection systems are defeated by an attacker, the deployment is still
protected by the remaining viable systems.
The NSA’s Information Assurance Technical Framework (IATF) [50] identifies the best current
practice for securing network and information systems. This approach provides defense-in-depth
protections at strategic locations within a network deployment. Each of these strategic locations
needs to have their own set(s) of security controls. These strategic defense locations include:
• Defend the network perimeter (i.e., the AS).
• Defend the enclave boundaries (e.g., communities of interest within the AS).
• Defend each computing device.
• Defend each application.
Figures 14 and 15 show the defense and in-depth provisions at each strategic defense location.
These provisions cumulatively form overlapping protection systems such that protection still
exists even if an entire system fails. Specifically, applications are partially protected by OS
protections. OS protections are partially protected by enclave protections. Enclave protections
are partially protected by network defenses.
Defend the Perimeter
Defend the
Enclave
Defend the
Computer
Figure 14. Overlapping Defense-in-Depth IA Systems
Defense-in-depth specifically means that redundant controls at each strategic defense location
form a constituent part of the system design. For example, firewalls traditionally comprise part
of a network’s perimeter defense protections. However, as section 4.1 has already explained,
there are three well-known attack vectors by which firewall protections can be defeated. For this
reason, additional protections (e.g., VPNs, which can also function as enclave protections) are
needed at the perimeter defense to maintain network integrity if the firewall protections are
defeated.
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