axigate

AX.25 ↔ APRS-IS bidirectional gateway for networked TNCs. Connects to a KISS TNC over TCP or Unix socket and forwards packets to and from APRS-IS servers.

Features

• RF to Internet (RX iGate): decode packets from the TNC and forward them to APRS-IS with qAR path annotation
• Internet to RF (TX iGate): receive packets from APRS-IS and transmit them to RF via the TNC as encapsulated third-party packets
• Independent directions: enable either or both forwarding directions
• TCP or Unix socket TNC connection

Installation

Requirements: Linux, GCC or Clang, CMake.

git clone --recurse-submodules https://github.com/xdab/axigate.git
cd axigate
mkdir build && cd build
cmake .. -DCMAKE_BUILD_TYPE=Release
make
sudo make install

Alternatively, make release builds and make install builds and installs.

make install also installs the axigate.service systemd unit to /etc/systemd/system and reloads the daemon. Review the unit file and adjust it to your setup.

The build depends on two bundled git submodules: libtnc (AX.25 parsing, KISS framing) and libcomm (socket clients, polling).

Usage

By default no forwarding is enabled — pass -r and/or -i to turn directions on.

# RX iGate only: RF packets forwarded to APRS-IS
axigate --host 192.168.0.9 --port 8144 --call MYCALL --rf-to-is

# Bidirectional gateway
axigate --host 192.168.0.9 --port 8144 --call MYCALL --rf-to-is --is-to-rf

# TNC behind a Unix socket
axigate --socket /run/tnc.sock --call MYCALL --rf-to-is

# All options from a configuration file
axigate --config axigate.conf

Command-line options

Option	Description
-c, --config=FILE	Configuration file
-h, --host=ADDR	TNC host address
-p, --port=PORT	TNC TCP port (default: 8144)
-x, --socket=PATH	TNC Unix socket path
--is-host=HOST	APRS-IS server (default: rotate.aprs2.net)
--is-port=PORT	APRS-IS port (default: 14580)
--is-filter=FILTER	APRS-IS filter string
--is-passcode=N	APRS-IS passcode (default: -1)
--is-keepalive=N	Minimum seconds between APRS-IS keepalive logins (default: 300, 0 = off)
--udp-kiss-listen=PORT	UDP port listening for KISS packets to gate to APRS-IS (default: off)
--udp-tnc2-listen=PORT	UDP port listening for TNC2 packets to gate to APRS-IS (default: off)
-C, --call=CALL	Gateway callsign
-s, --ssid=N	Gateway SSID (default: 0)
-r, --rf-to-is	Enable RF to APRS-IS forwarding
-i, --is-to-rf	Enable APRS-IS to RF forwarding
-v, --verbose	Verbose logging
-V, --debug	Debug logging

Configuration file

With -c FILE / --config=FILE, options can be read from a file using key=value syntax and # comments. Keys mirror the long option names; see sample.conf for an annotated example.

# TNC connection (TCP or Unix socket)
host=192.168.0.9
port=8144
# socket=/run/tnc.sock

# Gateway identity (used for APRS-IS path annotation)
call=MYCALL
ssid=0

# APRS-IS connection
is-host=rotate.aprs2.net
is-port=14580
is-filter=m/20
is-passcode=-1
# is-keepalive=300  # minimum seconds between keepalive logins, 0 = off

# UDP injection inputs (0 = off); requires rf-to-is=true
# udp-kiss-listen=0
# udp-tnc2-listen=0

# Forwarding directions
rf-to-is=true
is-to-rf=false

# Log level: verbose or debug (omit for standard)
verbose=verbose

How it works

RF to APRS-IS:

1. Receive KISS frames from the TNC and decode them into AX.25 packets
2. Skip packets with empty payloads, packets containing RFONLY/NOGATE, and already-encapsulated packets (loop prevention)
3. Append qAR and the gateway callsign to the path
4. Convert to TNC2 format and send to APRS-IS

APRS-IS to RF:

1. Receive packets from APRS-IS in TNC2 format
2. Replace the path with the TCPIP marker and the gateway callsign
3. Encapsulate the original packet as a } third-party packet
4. Encode as KISS and send to the TNC

UDP injection:

Local tools (e.g. a cron job beaconing the igate status) can push packets to APRS-IS without a TNC. With --udp-tnc2-listen=PORT or --udp-kiss-listen=PORT, axigate listens for datagrams in TNC2 or KISS format and gates them like RF traffic (same validation, qAR annotation, loop prevention; requires rf-to-is). Each datagram should hold one KISS frame or one newline-terminated TNC2 line, e.g.:

echo 'MYCALL>APRS:>igate up' | nc -u -w1 127.0.0.1 28145

License

GNU General Public License v3.0 — see LICENSE.