You can read the article for an introduction of what dataflow tabular charts are for. This page is based on the man page so it is more of a reference document.


dtc -- dataflow tabular chart

SYNOPSIS [–config -f <config>] [–format <png txt svg>] <input1> [<input2> …] -o <out.png>


dtc takes a textual description of a dafatlow diagram and produces a graphical output of the diagram. It is very convenient to present complex transport and filtering systems in one synthetic view.

The goal of the graphical representation is to convey information that is not usually available on a standard architecture representation: those representations usually show functional dataflows with no details on the transport mechanisms. DTC represents the protocol layers across the whole dataflow, allowing to show which device or service processes which part of the protocol layers.

For example email.svg shows a simple, typical e-mail setup whereby the sender (on the right) sends e-mail to an SMTP server. The SMTP server saves e-mail in local files (maybe using Maildir). An IMAP server on the same system serves the local user. This diagram shows easily that a malformed e-mail message can reach right inside the protected domain.


dtc is available from Github.


The diagrams are composed of three types of lines:

  • Systems

    Systems are drawn in the background and represent the physical hardware performing functions on the dataflow. An input line describing a system simply contains the system name followed by a colon:

      DMZ server:
  • Functions

    Functions are typically processes that happen within a system and act on the dataflow. They correspond to vertical arrows in the output diagram. An input line describing a function is composed of -> followed by the function name, followed by the number of protocol layers that are filtered in brackets, followed by an optional list of icons that will be added at specific protocol levels:

      -> Firewall (3) [2,cisco.png;3,iptables.png]

    Here we define a firewall that would cross three protocol levels, and add two PNGs at level 2 and 3 (a strange firewall).

    Note that the number of protocol layers is linked to the number of layers in the diagram (see below), this has nothing to do with OSI layers.

  • Protocols

    A protocol stack is present between each function and contains the stack of protocols that these functions will use to exchange data. Each protocol is separated by a slash. A protocol name can be left blank (e.g. if the protocol used is irrelevant for the diagram) or named void in which case the box won’t be drawn at all (e.g. if no protocol is used for that layer in the current stack, but is used somewhere else. This is often the case when transport goes through tunnels.)

    Each protocol can also receive an arrow pointing left or right, which is used to show where security filtering happens. These are presented by adding < or > character to the left or right of the protocol name, followed by the arrow colour (which can be used to represent the strenght of the filtering, or the assurance level of the security function) and an optional reference character that will be printed in the arrow.

    Colours are indexes in the ‘sf_colours’ list in the INI files, otherwise correspond to blue, green, yellow, orange and red.

    All protocol input lines must contain the same number of protocols.

    For example, a file posted using DAV over HTTPS could be presented as such:

      Ethernet / <3 IP / <3 TCP / <3 SSL / <x,A HTTP / DAV file

    Meaning the file is carried over HTTP over SSL over TCP over IP over Ethernet, and a firewall with assurance level 3 filters IP, TCP and SSL, and a Web server with no assurance level fiters HTTP. Reference 1, 2, 3 will be automatically added to the IP, TCP and SSL layers, and reference A will be added to HTTP.

Refer to the EXAMPLES section for full examples of diagrams.


The configuration file allows to override a number of settings. See example to make the output more colourful than the default.

It is not currently possible to change the security function arrow colours.


  • --config|-f config

    Specifies a file that contains the configuration for the diagrams: sizes, colours and so on. If not specified, defaults to dtc.ini. All parameters have reasonable defaults if no configuration file is present.

  • --format

    Specifies the output format. png will produce a bitmap image. txt will produce a glamorous, RFC-style text diagram. SVG will produce standard vector graphics. The default is SVG.

  • --output

    Specifies the output file name. By default, an extension ‘.png’, ‘.svg’ or ‘.txt’ is appended to the input filename. If the input filename has the ‘.dtc’ extension, it will be removed. ‘-‘ specifies stdout.


-> Printer (5)
Ethernet / IP 4,4> / TCP 3,5> / ? / ?
-> Netfilter (3)
void / IP / TCP / ? / ?
-> CUPS (5)
void / IP / TCP / IPP 3,6> / IPP printing payload
-> IPP proxy (5)
void / IP / TCP / <2,3 IPP / IPP printing payload
-> Netfilter (3) [2,firewall.png]
Ethernet / <0,1 IP / <1,2 TCP / IPP / IPP printing payload
-> Application (5)

(The example firewall icon is from

The result of this diagram is included in the archive as print.png.


Empty lines at the end of the file are a bad idea.

Order of statements is important: First it’s ‘function’, then ‘protocol’. System lines must come after a dataflow line.


Written by Yves Rutschle