DISCUSSION [NIST SP 800-171 R2]

Communications can be monitored, controlled, and protected at boundary components and by restricting or prohibiting interfaces in organizational systems. Boundary components include gateways, routers, firewalls, guards, network-based malicious code analysis and virtualization systems, or encrypted tunnels implemented within a system security architecture (e.g., routers protecting firewalls or application gateways residing on protected subnetworks). Restricting or prohibiting interfaces in organizational systems includes restricting external web communications traffic to designated web servers within managed interfaces and prohibiting external traffic that appears to be spoofing internal addresses.

Organizations consider the shared nature of commercial telecommunications services in the implementation of security requirements associated with the use of such services. Commercial telecommunications services are commonly based on network components and consolidated management systems shared by all attached commercial customers and may also include third party-provided access lines and other service elements. Such transmission services may represent sources of increased risk despite contract security provisions. NIST SP 800-41 provides guidance on firewalls and firewall policy. NIST SP 800-125B provides guidance on security for virtualization technologies.

FURTHER DISCUSSION

Fences, locks, badges, and key cards help keep non-employees out of your physical facilities. Similarly, your company’s IT network or system has boundaries that must be protected. Many companies use a web proxy and a firewall.

When an employee uses a company computer to go to a website, a web proxy makes the request on the user’s behalf, looks at the web request, and decides if it should let the employee go to the website.

A firewall controls access from the inside and outside, protecting valuable information and resources stored on the company’s network. A firewall stops unwanted traffic on the internet from passing through an outside “fence” to the company’s networks and information systems. Internal boundaries determine where data can flow, for instance a software development environment may have its own boundary controlling, monitoring, and protecting the data that can leave that boundary.

You may want to monitor, control, or protect one part of the company network from another. This can also be accomplished with a firewall and limits the ability of attackers and disgruntled employees from entering sensitive parts of your internal network and causing damage.

Example

You are setting up the new network and want to keep your company’s information and resources safe. You start by sketching out a simple diagram that identifies the external boundary of your network and any internal boundaries that are needed [a,b]. The first piece of equipment you install is the firewall, a device to separate your internal network from the internet. The firewall also has a feature that allows you to block access to potentially malicious websites, and you configure that service as well [a,c,e,g]. Some of your coworkers complain that they cannot get onto certain websites [c,e,g]. You explain that the new network blocks websites that are known for spreading malware. The firewall sends you a daily digest of blocked activity so that you can monitor the system for attack trends [c,d].

Potential Considerations

What are the external system boundary components that make up the entry and exit points for data flow (e.g., firewalls, gateways, cloud service boundaries), behind which all system components that handle regulated data are contained? What are the supporting system components necessary for the protection of regulated data [a]?

What are the internal system boundary components that make up the entry and exit points for key internal data flow (e.g., internal firewalls, routers, any devices that can bridge the connection between one segment of the system and another) that separate segments of the internal network – including devices that separate internal network segments such as development and production networks as well as a traditional Demilitarized Zone (DMZ) at the edge of the network [b]?

Is data flowing in and out of the external and key internal system boundaries monitored (e.g., connections are logged and able to be reviewed, suspicious traffic generates alerts) [c,d]?

Is data traversing the external and internal system boundaries controlled such that connections are denied by default and only authorized connections are allowed [e,f]?

Is data flowing in and out of the external and key internal system boundaries protected (e.g., applying encryption when required or prudent, tunneling traffic as needed) [g,h]?

Copyright

Copyright 2020, 2021 Carnegie Mellon University and The Johns Hopkins University Applied Physics Laboratory LLC.

Copyright 2021 Futures, Inc.

This material is based upon work funded and supported by the Department of Defense under Contract No. FA8702-15-D-0002 with Carnegie Mellon University for the operation of the Software Engineering Institute, a federally funded research and development center, and under Contract No. HQ0034-13-D-0003 and Contract No. N00024-13-D-6400 with the Johns Hopkins University Applied Physics Laboratory LLC, a University Affiliated Research Center.

The view, opinions, and/or findings contained in this material are those of the author(s) and should not be construed as an official Government position, policy, or decision, unless designated by other documentation.

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