tsunagi/README.md

tsunagi

A proof-of-concept Rust library for small private mesh networks — a handful of friends, home machines, a few servers. Units to dozens of participants, not thousands.

The end user configures exactly two things:

network_name
secret          # one shared secret; "password" and "secret" mean the same value

From those, every agent independently derives the same network space. There is no central server, no network owner with special powers, no registration and no majority vote. Anyone who knows the parameters can join; nobody has to trust anybody else.

What this proof of concept actually does

A working library with real iroh connections and integration tests:

• persistent device identity stored in SQLite, stable across restarts;
• several independent networks at once in one agent;
• deterministic network identity derived from name + secret;
• candidates supplied by a replaceable discovery component;
• real iroh connections plus an explicit mutual proof of network membership;
• a small versioned control protocol: handshake, hostname/capability announcement, ping/pong;
• automatic reconnect with bounded exponential backoff and jitter;
• status snapshots, an event stream and honest diagnostics;
• configuration restored after a restart;
• correct behaviour when the disposable cache is missing or corrupt;
• a WireGuard data plane, in userspace: its own key per network, an IPv6 overlay with deterministically derived addresses and optional IPv4, real tunnels carried over iroh, and address ownership enforced rather than believed;
• a command line agent, tsunagi, with a local control socket.

What it deliberately does not do

Not implemented, and not pretended to be: Mainline DHT, DNS, routing through intermediate participants, a full CRDT, dynamically loaded plugins, a system service, a complete CLI, or a local control socket. Snapshot synchronisation and signed revocations are designed for but not implemented — see docs/sync-model.md. The WireGuard plugin's own limits, including that its system backend is Linux-only, are in docs/wireguard.md.

Control and data are separated logically, not physically. Both ride on iroh, on different ALPNs and different connections, so the data plane inherits iroh's hole punching and relay fallback instead of reimplementing them — while the control protocol still knows nothing about packets and can keep a different transport underneath it later. Filtering user traffic remains the operating system's and the user's responsibility, not this library's.

Requirements

• Rust 1.91 or newer (iroh 1.2 requires it), edition 2024. Pinned dependencies in Cargo.lock.
• No internet, no DHT, no public relay, no administrator rights and no changes to OS network settings are needed to build or test.
• WireGuard runs in userspace (boringtun): no kernel module and no wg tool. Only creating a real network interface needs CAP_NET_ADMIN, and --no-tun skips even that.

Trying it on two machines

On the first machine:

cargo build --release
./target/release/tsunagi secret          # prints tsn1...; share it privately
./target/release/tsunagi doctor          # what this host can and cannot do

./target/release/tsunagi up --network lab --secret "$SECRET" --wireguard

It prints its endpoint id and then waits. On the second machine, pass that id:

./target/release/tsunagi up --network lab --secret "$SECRET" --wireguard \
  --peer <endpoint-id-from-the-first-machine>

Within a few seconds both print something like:

  + peer b47c958462 connected over Direct rtt=Some(4.5ms)
  + data link to b47c958462 for wireguard: Direct via Ip(…), datagram 1382

--- status ---
control: 1 peer(s), 0 dial failure(s), 0 handshake failure(s)
wireguard: tsunkkcp43lmdje on fd15:1d9e:fa21:f201:…/64 mtu 1280, 1/1 tunnel(s) established
  4jO4kx9Z fd15:1d9e:fa21:f201:… handshake 3s ago tx=0 rx=0 dropped=0 path=Direct via Ip(…)

1/1 tunnel(s) established means a real WireGuard handshake completed.

Checking that it works

From another shell on either machine:

tsunagi status

endpoint  7d76ccbbc21bf30767e14422c0494740a2cecc02aa9f82d5b8d57bdae350e7fc
hostname  tsunagi-7d76ccbbc2
bound     0.0.0.0:41641

network lab (z2o4qwrvnj3zb6st2aoqg4abf342j662q2ujttqrsmz22argk2ba)  active
  peer b345d5271b  tsunagi-b345d5271b  Direct  rtt 24ms
  overlay tsunz2o4qwrvnj3 fd09:…:c1c6/64 and 100.110.49.177 mtu 1280  1/1 tunnel(s) up
    SDsEb/WF  fd09:…:c4b / 100.65.243.53  handshake 4s ago  tx 0 rx 0  Direct via Ip(…)

1/1 tunnel(s) up and a recent handshake mean the tunnel is live. Then send real traffic to the peer's overlay address:

ping6 fd09:…:c4b        # or
ping  100.65.243.53

tx and rx in the status should start moving.

IPv6 works out of the box: each member's address is derived from the network id and collides with essentially nothing.

IPv4 addresses are allocated and then remembered. The default range is 10.13.37.0/24; the first member to join settles it and later members adopt what they find, so --ipv4-range only matters for whoever starts the network:

tsunagi up --network lab --secret "$SECRET" --wireguard --ipv4-range 10.44.0.0/16
tsunagi up --network lab --secret "$SECRET" --wireguard --ipv4-range none   # IPv6 only

An address is claimed with a record signed by that member's persistent device key, stored, and merged between every replica. A member that disappears for a month comes back to the same address, because the claim outlived the session. No vote is involved — see docs/wireguard.md and docs/sync-model.md.

Because the address is allocated at run time rather than derived, it is not known until the agent has started and agreed with its peers. The agent then assigns it to the interface itself.

Privileges

On Linux the agent manages its own overlay interface. It creates the TUN interface, sets the MTU, brings it up and assigns both overlay addresses, all over netlink in process — no ip invocation, no shell, nothing that a remote peer could influence.

That needs CAP_NET_ADMIN, granted once:

sudo setcap cap_net_admin+p /usr/local/bin/tsunagi

+p rather than +ep: the capability is then permitted but not effective, and the agent raises it only around the handful of netlink calls that need it — a few milliseconds at startup, and again if its address allocation changes. Everything else, including every byte from the network, is handled with it lowered. +ep works too; the agent lowers it on the way in.

tsunagi doctor says which of these applies on the host it runs on.

It cleans up after itself

The interface is tied to an open file descriptor and is deliberately not made persistent, so the kernel removes it when the agent exits — on a clean shutdown, on a panic, on SIGKILL, on power loss alike. Keeping it is what would take an action; removing it is the default.

If something is left behind anyway — an interface made by an older version's manual recipe, or one from a run killed in the instant between creating it and recording it — the next start replaces it, along with any stale addresses it carried. Two things are never touched:

• an interface that is not a TUN, because the name colliding with somebody's bridge is not a reason to destroy the bridge;
• a TUN that another process is holding open, because that is a working overlay belonging to somebody else — most likely a second agent on this host, which should be given a different --wg-prefix.

Both of those refuse with an explanation rather than guessing.

Two settings the manual recipe used to need are gone with it. keep_addr_on_down existed only because an interface nobody held open lost carrier and had its IPv6 addresses flushed, and nodad only because duplicate address detection can never finish without carrier. An interface held open for its whole life has carrier for its whole life.

The MTU is 1280

That is the minimum IPv6 requires (RFC 8200), and Linux enforces it by disabling IPv6 outright on an interface below it — the per-device /proc/sys/net/ipv6 entries vanish and adding an address fails with Invalid argument. A smaller MTU cannot work at all, so the agent refuses one rather than letting it fail later. See docs/wireguard.md for the ceiling that pushes back from the other side.

Summary

approach	agent runs as	notes
setcap cap_net_admin+p	ordinary user, one capability	recommended: nothing to prepare, nothing left behind. Lost on every rebuild or copy of the binary.
systemd service	User=, AmbientCapabilities=CAP_NET_ADMIN	the same, for an installed service
sudo tsunagi up	root	everything works, nothing is isolated
--no-tun	ordinary user, no capabilities	tunnels run and handshake, traffic never reaches the OS

Not implemented yet. macOS and Windows have no provisioner: both need real platform work — utun and SystemConfiguration on one, the IP Helper API and a Wintun adapter on the other. There the agent says so and --no-tun is the way to run it; the control plane and the tunnels are unaffected. The decision logic that says what to change is shared and tested on every platform, so only the execution is left to write.

Checks

cargo fmt --all -- --check
cargo clippy --locked --workspace --all-targets -- -D warnings
cargo test --locked --workspace --all-targets

The whole suite runs offline on loopback. Set TSUNAGI_TEST_LOG=tsunagi=debug to see agent logs while a test runs.

There are also two runnable demos, which are demos and not substitutes for the tests:

cargo run --example two_agents       # control plane only
cargo run --example wireguard_mesh   # a WireGuard overlay carrying a real packet

Both run with no privileges and change nothing on the host.

Usage

use std::sync::Arc;
use tsunagi::config::{AgentConfig, StoragePaths, TransportPolicy};
use tsunagi::discovery::SharedMemoryDiscovery;
use tsunagi::identity::{NetworkName, NetworkSecret};
use tsunagi::proto::ControlMessage;
use tsunagi::{Agent, Result};

// The library never starts a runtime, installs a logger, handles signals,
// forks, or calls process::exit. The binary owns all of that.
#[tokio::main]
async fn main() -> Result<()> {
    let config = AgentConfig::new(StoragePaths::user_default()?)
        .with_transport(TransportPolicy::N0Defaults)
        .with_discovery(Arc::new(SharedMemoryDiscovery::new()));

    let agent = Agent::spawn(config).await?;

    let name = NetworkName::new("kitchen-table")?;
    let secret = NetworkSecret::generate();       // 32 random bytes
    println!("share this: {}", secret.encode().as_str());

    let network = agent.join_network(&name, &secret).await?;

    let mut events = agent.subscribe();
    tokio::spawn(async move {
        while let Ok(event) = events.recv().await {
            println!("{event:?}");
        }
    });

    for peer in agent.network_status(network).await?.connected_peers() {
        agent
            .send(network, peer, ControlMessage::Ping { seq: 1, payload: vec![] })
            .await?;
    }

    agent.shutdown().await;
    Ok(())
}

TransportPolicy::LocalOnly is the default, so a plain AgentConfig::new never reaches the internet by accident. Opt into DirectOnly or N0Defaults explicitly.

How peers find each other

Two different lookups are involved, and only one of them is this project's:

1. Resolving one endpoint's address — iroh's, and it works today. With --transport relay or --transport direct, iroh publishes a signed record of this endpoint's addresses, keyed by its endpoint id, to the public service run by Number 0 — "n0", the company behind iroh — at dns.iroh.link, over pkarr and DNS, and resolves other endpoints the same way. That is why --peer <endpoint-id> works with no address attached: iroh looks it up. None of that code is ours.

2. Finding who is in a network — ours, and it is still manual. NetworkDiscovery maps a secret-derived DiscoveryKey to a set of candidate members. Two backends exist: StaticBootstrap (what --peer feeds) and an in-memory one for tests. The planned Mainline DHT backend, which would let members find each other from the network secret alone, is not implemented. So today you bootstrap by passing one peer's id; after that the mesh is whatever those agents reach.

What this means in practice:

• With relay or direct, your endpoint id and IP addresses are published to a public third-party service (Number 0's, unless you change it). They are not secret, and the network secret is never published, but an observer of that service learns that your endpoint exists and where it is. --transport local publishes nothing.
• A relay, when one is needed, sees the volume and timing of your traffic — not its contents. The default relays are Number 0's, in the US, EU and Asia-Pacific.

Storage

Two physically separate SQLite files, placed wherever the library's configuration says (StoragePaths). A future system service supplies its own paths; tests always use temporary directories.

file	holds	when damaged
state.sqlite	device identity, network configuration, hostname	clear error, never reset
cache.sqlite	address hints and other recoverable data	discarded and recreated

The WireGuard plugin keeps its own keys in its own wireguard.sqlite, wherever its configuration points, because plugin keys are neither the iroh identity nor the network secret.

The command line agent puts everything under the platform's per-user directories by default; --state-dir and --cache-dir override them.

One state directory belongs to one live agent, enforced with a real OS file lock rather than an existence check.

Documentation

• docs/architecture.md — module boundaries and runtime.
• docs/wireguard.md — the WireGuard plugin: overlay addressing, announcements, backends, reconciliation.
• docs/protocol.md — identity derivation, framing, handshake.
• docs/sync-model.md — the planned signed-state model and what is deliberately not built yet.
• docs/threat-model.md — threat model and known limits.
• docs/testing.md — what the suite covers and what it does not.
• AGENTS.md — rules for anyone (human or agent) changing this repo.

Security in one paragraph

Membership is proved by an HMAC over a transcript keyed by a value derived from the shared secret, bound to the specific iroh connection through the TLS exporter, to the network id, to both endpoint identities and to distinct role labels. This targets high-entropy secrets: there is no PAKE here, so a short human passphrase is guessable offline by anyone who can reach the handshake. Anyone who knows the secret is a full participant and can create many identities. Read docs/threat-model.md before relying on any of this.

Licence

MIT OR Apache-2.0.