AmiTCP_NG

A modernised, open TCP/IP stack for 68k AmigaOS — a fork of AmiTCP/IP 3.0b2 brought up to date with a current cross-toolchain, extensively documented, and extended into a drop-in replacement for Roadshow's bsdsocket.library.

Three things it is, in one breath:

1. A fork of AmiTCP/IP 3.0b2. The BSD networking core and the AmigaOS integration descend directly from the GPL AmiTCP/IP 3.0b2 sources.
2. A drop-in replacement for Roadshow. It provides the same bsdsocket.library API and the same configuration model and command set, so existing Amiga network software — and Roadshow's own configuration tools — work against it unchanged, with no time limit.
3. A clean-room re-implementation of the Roadshow extensions. The Roadshow-specific bsdsocket.library extensions were re-implemented from scratch, using Olaf Barthel's open-source Roadshow SDK purely as a reference for the published ABI (function offsets, tag values, structure layouts, documented behaviour). No Roadshow code is used, copied, disassembled, or redistributed — see Attribution.

The stack ships as a self-starting LIBS:bsdsocket.library: drop it in, and it brings the whole TCP/IP stack up by itself the first time any program opens it. (A standalone amitcp program build exists too.)

Not affiliated with, and not derived from, Roadshow. This project does not crack, patch, disassemble, or bypass Roadshow or any other commercial stack. Its goal is interoperability through an independent, open implementation of a published ABI.

Features

• BSD sockets — the full bsdsocket.library API (TCP, UDP, raw) on a drop-in Roadshow ABI, so existing Amiga software works unchanged, with no time limit.
• Protocols — TCP, UDP, ICMP, IP with routing and broadcast, ARP.
• Interfaces — any SANA-II device, plus software loopback (lo0, always on).
• Addressing — DHCP client, static, or RFC 3927 link-local when no DHCP server answers.
• Names — DNS resolver (gethostbyname, getaddrinfo, the reentrant gethostby*_r), search domain, RAM-tiered cache.
• Modern TCP — SACK recovery (RFC 2018/6675, with D-SACK, PRR, NewReno), RFC 1323 window scaling and timestamps, RFC 6928 initial window, and header prediction that works while sending, not only receiving.
• Asynchronous socket events — SO_EVENTMASK, SBTC_SIGEVENTMASK and GetSocketEvents(): the AmiTCP V4 mechanism Roadshow-era clients expect.
• Security-hardened — randomised ISNs (RFC 6528), RFC 5961 challenge-ACK limiting, broadcast and fragment DoS guards, and a whole-codebase memory-safety review.
• Packet capture (BPF) — filter, read or inject raw frames, and PacketCapture writes a pcap file you can open in Wireshark, so a failing network can be handed to someone who isn't sat at the Amiga.
• Diagnostics that ship — every build can log, off-screen by default; LOGLEVEL=7 names any library call that fails and the errno it failed with. No debug build to obtain.
• Roadshow-compatible tooling — the extension API and capability flags, the full 25-command set (Online, AddNetInterface, ShowNetStatus, ping, …, plus RoadshowControl under the name Roadshow scripts expect), shared library bases, and an Amiga Installer.
• Usable on its own — netstat, nslookup, ftp, tftp, sntp, arp, traceroute, PacketCapture, SampleNetSpeed (live per-interface throughput), NetLogViewer, CheckAmiTCPNGConfig and ManageNetInterfaces ship with it, so a freshly installed Amiga can fetch everything else itself.
• usergroup.library — the user/group/account library Roadshow ships, for software that expects it. Reads Roadshow's own DEVS:Internet/users and groups; independent of the stack.
• Self-tuning — socket buffers, SANA-II rings, the mbuf pool and the DNS cache size themselves to installed RAM and link speed; per-interface and stack-wide overrides are honoured.

Status

• Runs on emulated AmigaOS 3.2 and real 68k hardware as a self-starting LIBS:bsdsocket.library.
• Emulator-validated (A2065 over SLIRP): DNS, a full DHCP lease, ping, same-host broadcast and loopback, the socket-event mechanism end to end, and BPF capture whose pcap files were checked by reading them back with tcpdump on the host.
• Hardware-validated (PiStorm + wifipi.device): bring-up, DHCP, routing, DNS and connectivity over 100 Mbit WiFi — roughly 56 Mbit down / 52 up once the SANA-II transmit queue landed. Amiga Explorer works.
• Roadshow-compatible — name-, argument- and output-compatible, so Roadie, NetMon and existing scripts drive it unchanged.
• Measured, not assumed — the TCP work came from counters read off real hardware: header prediction was covering 98% of segments downloading and 9% uploading; the cause was the peer's moving window, and the fix took uploads to 57%.
• Tunable at run time — AmiTCPControl reads and changes the stack's internal options (AmiTCPControl on its own lists them all), the same command shape and option names Roadshow uses, so existing scripts work unchanged. SAVE keeps a setting across reboots. Options the stack sizes for itself from your machine's RAM, CPU and link speed accept a setting but keep the tuned value, saying so in the log — a script that sets them carries on instead of failing, and nobody is left wondering why their number is not the one in use.
• Paced ARP — the 4.3BSD base broadcast a fresh ARP request for every packet to an unresolved address, with no cap, and told the caller it had been sent. Now: one request a second, a bounded burst, then a hold-down that reports the host unreachable instead of transmitting into silence. A resolved entry is re-checked by unicast probe rather than trusted for twenty minutes, and ordinary inbound traffic confirms a peer is alive, so an active connection is never probed at all.
• One build for every Amiga — a single 68000 archive that picks its copy routine at run time from the CPU it finds itself on.
• Deferred — IP filter (ipf_*), monitor hooks, server API (docs/DEFERRED-VECTORS.md); IP multicast receive is not implemented.

Installing

Grab the release .lha (or the .adf floppy image) and run its Install-AmiTCP_NG Installer script on your Amiga.

There is one archive, and it runs on every 68k Amiga. There used to be separate -68020 and -68040 builds; they were dropped because compiling for those processors was proven in real-world testing not to make the stack any faster, so the only thing the extra archives reliably did was let someone install a build their machine could not run. The decisions that genuinely do depend on the processor — which memory-copy routine to use — are made at run time, inside this one binary. How much it asks depends on the user level you pick in the Installer's opening dialog (the standard Amiga Installer Novice / Intermediate / Expert choice):

• Novice — the installer asks nothing and takes every default:

  • It installs the AmiTCP drawer (its configuration + host database) to SYS:Programs/AmiTCP — or SYS:AmiTCP if you have no Programs drawer.
  • If it detects an existing TCP/IP stack (a bsdsocket.library, e.g. Roadshow), it automatically upgrades in place: it backs up and swaps in AmiTCP_NG's bsdsocket.library, and installs AmiTCP_NG's own command set over the existing tools (originals backed up to C:<name>.orig). Replacing the commands is required — Roadshow's own config tools drive AmiTCP_NG down an interface-setup path that hangs, so the command set must be AmiTCP_NG's too. Your interface configuration is left untouched, and it all runs with no time limit. On a clean machine it does a full install (library + the whole command set + a network startup + example configs).

• Intermediate / Expert — unlocks the extra choices:

  • Choose where the AmiTCP drawer goes (any volume or drawer).
  • Preview — show exactly what an install would do, changing nothing.
  • Uninstall / roll back — restore the library (and command) that were backed up by an upgrade, or remove what a full install added. Uninstall is only offered above Novice level.

Reboot when the installer finishes. End-user details are in install/ReadMe.

Configuring your network from cold

AmiTCP_NG is configured the same way as Roadshow, so existing configurations work unchanged. There are two pieces: a per-interface file that says which hardware to use and how to get an address, and an optional stack file for global settings. In most cases the interface file is all you need.

1. Describe your interface — DEVS:NetInterfaces/<name>

Create one text file per network interface. The file's name is the interface name (so DEVS:NetInterfaces/eth0 defines interface eth0). The simplest possible file — get everything (address, netmask, router, DNS) from DHCP:

device=a2065.device
configure=dhcp

Or a fixed (static) address instead:

device=a2065.device
address=192.168.0.10
netmask=255.255.255.0
gateway=192.168.0.1
nameserver=192.168.0.1

Settings AmiTCP_NG acts on:

Key	Meaning
device=	Required. SANA-II driver. A bare name resolves to DEVS:Networks/<name>; a resident driver name (e.g. wifipi.device) is used directly.
unit=	Device unit number (default 0).
configure=dhcp	Lease the address / netmask / router / DNS via DHCP. Omit for a static setup.
address=	Static IPv4 address.
netmask=	Static subnet mask.
gateway=	Default-route gateway.
nameserver=	A DNS server. Repeat the line for more than one.
domain=	Default domain name.
requiresinitdelay=yes	Pause briefly after opening the device (some hardware needs a warm-up before it will configure).

Roadshow keys that AmiTCP_NG does not act on (iprequests, writerequests, filter, configure=auto/fastauto, debug) are accepted and ignored, so a Roadshow interface file drops in without edits.

2. Bring it up

AddNetInterface eth0

AddNetInterface reads DEVS:NetInterfaces/eth0 and brings the interface up — running the DHCP handshake or applying the static address as the file dictates. After that, Online/Offline toggle it, and ShowNetStatus reports the current state. A full install also drops in a boot-time S:Network-Startup script that does this for you at startup.

3. Stack-wide settings — AmiTCP:db/AmiTCP.config

Optional. One NAME=VALUE per line; # starts a comment. Read once when the stack starts. The knobs worth knowing:

Setting	Meaning
HOSTNAME=<name>	The host's own name — what gethostname() returns to applications.
MBUFCHECK=ON	Detect double frees and use-after-free in the packet buffers. Off by default; a diagnostic for chasing memory corruption, not something to leave on.
USENAMESERVER=SECOND	DNS resolution order: NO (local hosts table only), FIRST (ask DNS first), SECOND (local table first, then DNS).
GATEWAY=NO	Whether to forward IP between interfaces (act as a router).
TCP_SENDSPACE=<bytes>	TCP send-buffer size (overrides the auto-tuned default; see below).
TCP_RECVSPACE=<bytes>	TCP receive-buffer size (overrides the auto-tuned default).
LOGGING=ON|OFF	Keep a log at all. Default ON — a quiet file, nothing on screen.
LOGLEVEL=0..7	How much. Default 5. 7 also logs every failing library call and its errno, which is how you find out what a program is unhappy with.
LOGCONSOLE=ON|OFF	Also throw the log at a console window. Default OFF — the window puts itself in front of whatever you are doing.
LOGFILENAME=<path>	Default RAM:AmiTCP.log. Point it at a disk if you are chasing something that only clears with a reboot.
CONSOLENAME=<path>	Where LOGCONSOLE=ON opens its window. Default con:0/0/600/100/AmiTCPIP Log/AUTO/INACTIVE. Point it at a file and you get a second log file, not a window — CheckAmiTCPNGConfig warns if you have.

A minimal example:

HOSTNAME=my-amiga

CheckAmiTCPNGConfig reads all of this back and reports anything wrong, without starting the stack or touching the hardware.

4. Host, service and protocol names

AmiTCP_NG reads its own AmiTCP:db/netdb and Roadshow's files if you have them — DEVS:Internet/hosts, networks, protocols and services — so a machine upgraded from Roadshow keeps everything it had. They add to what netdb already defines rather than replacing it, and a missing file is perfectly normal.

5. It tunes itself to your machine and your link

You normally do not need to touch the buffer sizes. AmiTCP_NG sets the TCP window automatically from two things, and uses the smaller of them:

• Your RAM sets the ceiling. The socket buffers are backed by an mbuf pool sized to installed RAM, so a small machine stays lean and a big one can afford a large window:

  Installed RAM	Window ceiling
  ≤ 1 MB (e.g. 512K A500)	~16 KB (lean enough to still boot)
  2–4 MB	~61 KB
  8–16 MB	~128 KB
  16–64 MB	~256 KB
  64–128 MB	~512 KB
  128 MB+ (PiStorm-class)	~1 MB

• Your link speed sets the target. The window that fills a link without overshooting is its bandwidth-delay product, so the stack reads each NIC's link speed and sizes the window to it — ~512 KB for a ~100 Mbit link, ~1 MB for gigabit — never above the RAM ceiling. A window larger than the link needs doesn't add throughput and hurts loss recovery, so on a big-RAM machine a 100 Mbit NIC is deliberately held to ~512 KB, not 1 MB. (A driver that doesn't report its speed simply falls back to the RAM ceiling.)

RFC 1323 window scaling makes the >64 KB windows possible and is negotiated per connection; timestamps are enabled on a 68020+ and left off on a bare 68000/68010 (where the per-segment cost is not worth it).

To override, set tcp.sendspace=/tcp.recvspace= in a DEVS:NetInterfaces interface config (this is stack-wide — the last interface configured wins) or TCP_SENDSPACE=/TCP_RECVSPACE= in AmiTCP.config. Run GetNetStatus DEBUG to see the RAM the stack detected and the window it chose.

Two more stack-wide TCP tunables use the same mechanism (tcp.<name>= in an interface config, or the upper-case <NAME>= in AmiTCP.config): tcp.mssdflt / TCP_MSSDFLT — the off-subnet MSS cap in bytes (0 = auto: interface MTU − 40); and tcp.iw / TCP_INITIALWINDOW — the initial congestion window in segments (10 = RFC 6928 default, 4 = RFC 3390, 1 = legacy single-segment slow-start).

Build & test

Everything runs in disposable Docker containers — you need only Docker on the host. docs/BUILDING.md is the full guide (compiling the tools, rolling your own .lha/.adf, and testing your own code); the harness internals are in docker/README.md.

# The self-starting drop-in library  ->  build/bsdsocket.library
./docker/build-lib.sh

# The full Roadshow-compatible command set  ->  build/Online, build/ping, ...
./docker/build-tools.sh

# LIBS:usergroup.library  ->  build/usergroup.library
./docker/build-usergroup.sh

# A complete installable release  ->  build/release/AmiTCP_NG.lha  and  .adf
./docker/build-release.sh

# Test: fast loopback / API tests, then real-network tests (A2065 + SLIRP + DHCP)
TIMEOUT=95 ./docker/run-fsuae.sh
NET=1 TIMEOUT=150 ./docker/run-amiberry.sh

To run the emulators you must supply your own licensed Amiga system files (a Kickstart ROM and an AmigaOS 3.2 install). These live under emu/, which is git-ignored and never committed — see the docker guide.

Repository layout

Path	Contents
src/	The TCP/IP stack: AmigaOS integration (kern/, api/), BSD networking core (net/, netinet/), the drop-in library (lib/), headers (netinclude/).
src/tools/	The Roadshow-compatible command-line tools (source), sharing ng_lvo.h.
src/usergroup/	LIBS:usergroup.library — the user/group/account library Roadshow ships. Independent of the stack.
install/	The Amiga Installer script, its ReadMe, the network database, Network-Startup, and example interface configs.
docker/	The build/test harness — Dockerfiles, scripts, and per-image how-to READMEs.
docs/	BUILDING.md, ARCHITECTURE.md, COMMENTING.md, REVIEW_FINDINGS.md, DEFERRED-VECTORS.md.
COPYING / COPYRIGHTS	GPL v2, and the retained original AmiTCP/IP copyright notices.

Buy me a coffee ☕

This is a hobby project, done for the love of the Amiga — not to make money, and it will always be free. But if it's useful to you and you fancy buying me a coffee, that's very kind: https://paypal.me/AndyTaylorTweet. Entirely optional, and thank you either way.

License

AmiTCP_NG is licensed under the GNU General Public License, version 2 (see COPYING), consistent with its AmiTCP/IP heritage.

• AmiTCP_NG modifications and new code: Copyright © 2026 Andy Taylor (MW0MWZ). Modified and new source files carry this notice; original AmiTCP/IP and BSD copyright notices are retained alongside.
• AmiTCP/IP 3.0b2: Copyright © 1993, 1994 AmiTCP/IP Group, Helsinki University of Technology (see COPYRIGHTS).
• BSD networking code: Copyright © the Regents of the University of California, under the original BSD license (retained in the affected files).

Attribution — the Roadshow SDK (reference only)

AmiTCP_NG's Roadshow-compatible bsdsocket.library extensions are a clean-room re-implementation. They were written from scratch using Olaf Barthel's Roadshow SDK as the authoritative reference for the ABI: the extension function offsets, tag values, structure layouts, and documented behaviour all come from the SDK's autodoc, SFD files, and headers. Reading that published documentation (and the SDK's example command sources, and strings on published binaries) is legitimate interoperability work — no Roadshow code is reused, copied, disassembled, or included here. Our implementation is our own.

We are genuinely grateful that Olaf Barthel made the Roadshow SDK openly available. This project simply could not match the ABI so precisely without that documentation, and we thank him for it.

The Roadshow SDK and its sample sources are Copyright © Olaf Barthel / APC&TCP, All Rights Reserved, and are not included in this repository. To build or verify against the SDK reference, obtain it directly from its author:

• Roadshow: http://roadshow.apc-tcp.de/
• Roadshow SDK: https://www.amigafuture.de/app.php/dlext/details?df_id=3658

Roadshow is a commercial product. AmiTCP_NG is an independent, open implementation of the same published ABI — neither derived from, nor affiliated with, Roadshow — and does not include, modify, or bypass any Roadshow code.