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PacketDiag — Protocol Header Diagrams

PacketDiag generates byte-accurate network protocol header diagrams. Fields are defined by bit position ranges and can carry color, rotation, and spanning attributes.

!!! tip "Syntax" Use start-end: Label; to define a field. [rotate = 270] rotates short labels vertically. [colheight = N] makes a field span multiple rows.

UDP Header

The complete 64-bit User Datagram Protocol header with color-highlighted fields.

blockdiag 0 16 32 Source Port Destination Port Length Checksum

TCP Header

The full 224-bit TCP header including flags with rotated labels, window, checksum, and options.

blockdiag 0 16 32 Source Port Destination Port Sequence Number Acknowledgment Number Data Offset Reserved CWR ECE URG ACK PSH RST SYN FIN Window Checksum Urgent Pointer (Options and Padding) data

EtherCAT Frame Header

An industrial EtherCAT Ethernet frame header layout — an example of field-bus protocol documentation.

blockdiag 0 16 32 Destination MAC Source MAC EtherType (0x88A4) Length Rese rved Type EtherCAT Datagram Destination MAC Source MAC EtherCAT Datagram EtherCAT Datagram EtherCAT Datagram