AX.25 without the kernel

Section 1

Why the gateway changed

Linux 7.1 drops the kernel AX.25 stack. Every program that does socket(AF_AX25, …) — ax25d, axspawn, call, DX cluster doors, mailboxes — needs somewhere else to go.

iw2ohx-gw used to carry a full Linux packet stack: kernel interfaces ax0/ax1/ax2, kissattach on pty pairs, two ax25ipd, kernel NET/ROM, flexnetd and URONode. Most of that duplicated what LinBPQ IW2OHX-13 (with our FlexNet extension) already does better: routing, NET/ROM, FlexNet, user commands. So the change came in two steps on the same day:

Step 1

URONode retired. LinBPQ IW2OHX-13 became the only node on the host. IW2OHX-7, IW2OHX-3 (flexnetd) and OHXGW:IW2OHX-1 (kernel NET/ROM) are gone. Their services are LinBPQ applications now: DX, CONV, IGATE, SHELL.

Step 2

Kernel AX.25 replaced by WAMPES. The few Linux programs that still need AX.25 — the DXSpider door, the shell login and a telnet gate — now reach it through WAMPES in user space, via the userspace build of libax25 (unix-ax25-stack, DL9SAU). The kernel modules are blocked; the host already runs as it will on 7.1.

Section 2 — the idea

A connector, not a node

WAMPES can be a complete node. Here it is deliberately not: it does no routing, carries no FlexNet and relays nothing between its ports. It only adapts.

One AXUDP link on loopback joins the node and the connector; the service socket joins the connector and Linux

LinBPQ

Owns the network: RF, FlexNet, NET/ROM, telnet logins, every user command. Its port 7 is a plain BPQAXIP port pointing at 127.0.0.1.

WAMPES

Claims two callsigns with listen ax25 add … client: IQ2LB-6 (the cluster) and IW2OHX-11 (the shell). A connect to either is handed, as an open descriptor, to whichever program has bound that callsign over the service socket. Nothing else is answered or forwarded.

libax25

The userspace build intercepts socket, bind, connect, listen, accept. At bind() it sees that the port belongs to a WAMPES node (listed in wampes.conf) and moves the socket there. After connect() the program holds a plain byte stream — nothing of the library is left on the data path. ax25d and axspawn run unmodified.

Section 3

One session, step by step

A user at the BPQBOL prompt types DX.

1. LinBPQ runs the application DX = C 7 IQ2LB-6: an AX.25 SABM on port 7, from the user's own callsign to IQ2LB-6.
2. BPQAXIP wraps the frame in UDP to 127.0.0.1:10095 (MAP entry for IQ2LB-6).
3. WAMPES iface bpq receives it and learns the user's callsign → 127.0.0.1:10096 for the replies (axip-learn on).
4. IQ2LB-6 has a client listener, and ax25d holds it: WAMPES accepts the link and hands the session over the service socket.
5. ax25d matches [IQ2LB-6 VIA wampes] and starts the DXSpider client as user sysop, with the session on stdin/stdout and the caller's callsign as argument.
6. DXSpider greets the user by their callsign — the identity survived every hop.

SHELL is the same path to IW2OHX-11, where ax25d starts axspawn → /bin/login. As at DB0FHN, the account is created on the first connect from the caller's callsign, and over AX.25 no password is ever asked — the callsign is the login. From that shell the user runs passwd if they also want the telnet gate (Section 6); a notice says so until a password is set.

Section 4

How to connect

The node is IW2OHX-13, NET/ROM alias BPQBOL. URONode callsigns IW2OHX-7, IW2OHX-3 and OHXGW are retired.

At the BPQBOL prompt: DX cluster, CONV convers (DB0FHN-12 via IGATE), IGATE, CHAT, BBS, XNET, BPQHF, SHELL, FL FlexNet links, D destinations.

Section 5 — copy the reasoning, not the numbers

Sample configurations

The live files of iw2ohx-gw, trimmed. WAMPES is built with TCPDIR=/tcp, libax25 and the ax25 tools with prefix /opt/uax25.

net.rc — the whole AX.25 side of the connector

Built with a prefix such as /opt/uax25, axspawn looks for useradd in that prefix — a symlink to /usr/sbin/useradd is needed, or every new account fails

LinBPQ binds port 7 on every address. Loopback is accepted earlier in the chain, so this DROP makes it reachable from the host alone.

After a WAMPES restart, ax25d notices the lost listeners and claims IQ2LB-6 and IW2OHX-11 again by itself within about ten seconds.

Section 6

The telnet gate: AX.25 as yourself

Modelled on the telnet port of DB0FHN, rewritten for this host.

1. Telnet to port 23 on iw2ohx.ampr.org or pr.iw2ohx.hamnet.radio. Only 44Net and HAMNET sources are let in.
2. Login: your callsign, SSID allowed. Station calls and NOCALL are refused before anything else.
3. Password: the one you set yourself with passwd after your first SHELL by radio, FlexNet or NET/ROM. An account without a password cannot log in here. Five failures lock it for 15 minutes.
4. The daemon drops root and opens an AX.25 connection from your callsign to IW2OHX-13 through WAMPES. You land at the BPQBOL prompt exactly as if you had come in by radio.

ax25telnetd is about 1,300 lines of C11: a telnet filter that strips every option negotiation and maps line ends (CR LF ↔ CR), the callsign rules, PAM, privilege drop and a relay loop. It is an ordinary libax25 program — socket(AF_AX25), bind to the user's callsign via the WAMPES port, connect — and contains no WAMPES-specific code at all. No account is handed out by mail: the first SHELL over packet radio creates it. The password travels in clear, so use one you use nowhere else.

Section 7

What cost us time

Commits used: libax25 1ff923b, ax25-tools 3b33d6b, ax25-apps b78e3cc, wampes c028c51 (October 2026), on a Raspberry Pi 4 with 64-bit Debian 13.

Section 8

Further reading

In the WAMPES source tree, doc/PERMISSIONS.md and doc/LIBAX25-BRIDGE.md, and in libax25 AX25-WITHOUT-KERNEL-SYSOP.md, explain the design far better than this page. Thanks to Thomas, DL9SAU, for keeping AX.25 alive on Linux.