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The below example has key information highlighted. (This example is "based" on a real system, but the hostnames/IP addresses and some of the details were made up to protect the innocent).  Your diagrams may not look exactly like this, but it should convey the same level of detail and amount of information to aid in the review process.  

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• Key pieces: Network segment subnet definitions, relevant hostnames/IPs, building routers and firewalls names if exist (switches unnecessary), OS/type of host, relationship to campus, Internet, or 3rd party networks.
• Visio Format

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• A data flow diagram illustrates how data flows throughout the system. It answers the questions:
  • How does data enter the system?
  • How and where does data travel within the system?
  • How does data exit the system?
  • How is data changed or transformed throughout the system?
  • Where is data stored?

• Key pieces: The hosts in your system that store or allow sensitive/restricted information to be transmitted through them, as well as all entry points of that data into the system, and all exit points of that data out of the system, and any flow of data within subsystems.  Arrows should denote the direction of data flow.  The type of data should be noted. The type of transport protocol, encryption, and any relevant access controls of data in transit should be noted.  The type of data storage, encryption, and any relevant access controls of data at rest should be noted.  Lines denoting boundaries of firewalled segments should be noted.

Drawing a Data Flow Diagram:

Step 1: Start off by drawing a context diagram

• A context diagram is a diagram that illustrates how the system works from start to finish. Anyone who views the context diagram should be able to understand at a high-level what is happening within the system.

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• Data Flow Diagram Notations:

  Title

Entity – creates

• Notation	Description
  Entity	Image Added	Entities create or use data.
  Process

–

• 	Image Added	Process - an activity that transforms or changes data.
  Data Store

– stores data

• 	Image Added	Data Store - a place where data is stored.
  Data Flow	Image Added	Data Flow – the movement of data. Arrows should denote the direction of data flow.

Step 2: Add a red dashed line for any firewalls being used.

Step 3: Add any technical processes that occurs within entities

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Step 4: Add information tags to all data flow arrows.

 Information tag includes:

• • Transport encryption
  • Data encryption
  • Data (highlight in red any P3/P4 data)
  • Service
  • Authentication
  • Authorization 

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• Data Flow Diagram

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• Key pieces: The hosts in your system that store or allow sensitive/restricted information to be transmitted through them, as well as all entry points of that data into the system, and all exit points of that data out of the system, and any flow of data within subsystems.  Arrows should denote the direction of data flow.  The type of data should be noted. The type of transport protocol, encryption, and any relevant access controls of data in transit should be noted.  The type of data storage, encryption, and any relevant access controls of data at rest should be noted.  Lines denoting boundaries of firewalled segments should be noted.
• Visio FormatExample.vsdx