# Packet Diagram (BlockDiag)

PacketDiag (part of Blockdiag) lets you describe the internal structure of network packets as text, and automatically renders them as packet header/format diagrams - the kind you'd see in RFCs and networking documentation.

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![Packet Diagram](https://diagrams.gocapable.com/images/att1226342540.svg)

```
packetdiag {
  colwidth = 32;
  node_height = 72;

  0-15: Source Port;
  16-31: Destination Port;
  32-63: Sequence Number;
  64-95: Acknowledgment Number;
  96-99: Data Offset;
  100-105: Reserved;
  106: URG [rotate = 270];
  107: ACK [rotate = 270];
  108: PSH [rotate = 270];
  109: RST [rotate = 270];
  110: SYN [rotate = 270];
  111: FIN [rotate = 270];
  112-127: Window;
  128-143: Checksum;
  144-159: Urgent Pointer;
  160-191: (Options and Padding);
  192-223: data [colheight = 3];
}

```