Packet diagram (PacketDiag)

PacketDiag maps bit ranges onto a fixed word width and draws the grid. It removes the entire class of errors that comes from drawing header diagrams by hand.

#What this example shows

• colwidth, which sets the word size.

• Inclusive bit ranges per field.

• Single-bit flag fields.

#A worked example

Open it, edit it, or copy the source below.

The source, which you can paste into a new diagram and edit:

packetdiag {
  colwidth = 32;
  node_height = 60;

  0-15: "Source port";
  16-31: "Destination port";
  32-63: "Sequence number";
  64-95: "Acknowledgement number";
  96-99: "Offset";
  100-105: "Reserved";
  106: "U";
  107: "A";
  108: "P";
  109: "R";
  110: "S";
  111: "F";
  112-127: "Window";
  128-143: "Checksum";
  144-159: "Urgent pointer";
}

#Making it your own

• colwidth must match the real word size or every offset misleads.

• Ranges are inclusive, so 0-15 is sixteen bits.

• For byte-oriented structures with nesting, use Bytefield.

#Related

Specialists. Borrow one when you need it.