axdigi

AX.25 layer 2 digipeater for networked TNCs.

What it is

A pure layer-2 AX.25 digipeater software that connects to KISS TNCs via TCP or Unix socket. It handles:

• Traced aliases (WIDE2-2, TRACE3-1) — decrements hops, prepends own callsign
• Untraced aliases (SP3-1, AROS3-1) — just decrements hops
• Own callsign digipeating — marks itself in path
• Basic packet deduplication — prevents most duplicate transmissions

What it isn't

This project is not:

• A TNC — just a digipeater, no modulation/demodulation
• APRS-aware — no filtering based on position, packet type, no beaconing, i-gating etc.
• Cross-platform — Linux-only (uses Unix sockets, signal handling)

Build

make update # pulls and updates submobules
make clean
make build # build with debug symbols, no optimizations
make release # build with all optimizations, strip symbols

Usage

# TCP TNC connection
axdigi -h 192.168.0.9 -p 8144 -C SR5DZ -s 0 -u SP,XR,ND -t WIDE,TRACE -U 2 -T 2

# Unix socket TNC
axdigi -x /run/tnc.sock -C SR5DZ -s 0

# Configuration file
axdigi -c axdigi.conf

# Dry run (no packets transmitted)
axdigi -n -C SR5DZ -s 0

Command Line Arguments

Short	Long	Description
-c FILE	--config=FILE	Configuration file
-h ADDR	--host=ADDR	TNC TCP address
-p PORT	--port=PORT	TNC TCP port
-x SOCK	--socket=SOCK	TNC Unix socket path
-C CALL	--call=CALL	Digipeater callsign
-s SSID	--ssid=SSID	Digipeater SSID (0-15)
-t ALIAS	--traced=ALIAS	Traced aliases (comma-separated)
-u ALIAS	--untraced=ALIAS	Untraced aliases (comma-separated)
-T N	--max-traced-hops=N	Max hops for traced aliases
-U N	--max-untraced-hops=N	Max hops for untraced aliases
-v LEVEL	--log-level=LEVEL	Log level: standard, verbose, debug
-n	--dry-run	Don't transmit packets

Configuration File

Optionally, configuration can be read from a file using -c FILE or --config=FILE.

The file uses simple key=value syntax with # comments.

Example

# axdigi.conf
host=192.168.0.9
port=8144
call=SR5DZ
ssid=0
aliases-traced=WIDE,TRACE
aliases-untraced=SP,XR,ND
max-traced-hops=2
max-untraced-hops=2
log-level=verbose
dry-run=false

Alias behavior

Traced aliases (e.g., WIDE, TRACE)

• Decrement hop counter on each digipeat
• Prepend own callsign (repeated=true) before the alias
• When hops reach 0, mark alias as repeated (NAME*)

For example: WIDE2-2 becomes SR5DZ*,WIDE2-1 and if somehow digipeated again would become SR5DZ*,SR5DZ*,WIDE2*.

Untraced aliases (e.g., SP, MZ)

• Decrement hop counter on each digipeat
• Do NOT prepend own callsign
• When hops reach 0, mark alias as repeated (NAME*)

For example: SP3-2 becomes first SP3-1 and then might become SP3* when bounced off another digi.

Dependencies

• libtnc: included as a git submodule
  • AX.25, KISS, CRC and networking routines

Installation

There is a helper Make target make install which handles everything from compilation to asking for SU rights and installing files to the relevant directories.

Systemd service axdigi.service will be installed as well. Please review the unit file and adjust for your needs.

License

GNU General Public License v3.0 - see LICENSE

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Development notes: See .clinerules for AI-friendly technical documentation.