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 is opt-in, because no IPv4 range is free on every host — 100.64.0.0/10 is Tailscale's, 10.0.0.0/8 and 192.168.0.0/16 are everywhere, 172.17.0.0/16 is Docker. Name one you know is unused, the same one on every member:

tsunagi up --network lab --secret "$SECRET" --wireguard --ipv4-range 10.77.0.0/16

The range is part of how addresses are derived, so members configured differently would misroute. It travels in the announcement purely so a mismatch is reported instead: the offending peer gets no IPv4 and keeps working over IPv6. See docs/wireguard.md.

Notes:

• Only one side needs --peer; the link is bidirectional.
• The default --transport relay uses iroh's public address lookup and relays, so two machines behind NAT find each other. --transport local keeps everything on the local network. See How peers find each other below — it is worth understanding what gets published.
• Without a network interface, add --no-tun: the mesh, the data links and the WireGuard handshakes all still run and are visible in the status output, only traffic does not reach the operating system. That is the quickest way to confirm the network forms.
• For real traffic, see Running unprivileged below.

Running unprivileged

The agent does not need to run as root. Creating a network interface and giving it an address do need privileges, but they are a one-time setup step that can be done separately.

Ask the agent what it needs, then run that once as root:

tsunagi tun-setup --network lab --secret "$SECRET"

# Interface tsunjwc6dcrtmo5, address fd80:1210:f724:f620:d1bb:f982:3b6e:19bd/64, mtu 1280
# Run once as root; then run `tsunagi up` as ab.

sudo ip tuntap add dev tsunjwc6dcrtmo5 mode tun user ab
sudo ip link set dev tsunjwc6dcrtmo5 mtu 1280 up
sudo sysctl -qw net.ipv6.conf.tsunjwc6dcrtmo5.keep_addr_on_down=1
sudo ip -6 address add fd80:1210:f724:f620:d1bb:f982:3b6e:19bd/64 dev tsunjwc6dcrtmo5 nodad

If you asked for IPv4 with --ipv4-range, tun-setup adds an ip address add line for it too.

The MTU is 1280 because that is the minimum IPv6 requires (RFC 8200). Linux disables IPv6 entirely on an interface below it — the per-device /proc/sys/net/ipv6 entries vanish and ip -6 address add fails with Invalid argument — so a smaller MTU cannot work at all. The agent refuses one rather than letting it fail later.

The order and the last two lines are not decoration. A persistent TUN interface has no carrier until a process attaches to it, and Linux flushes IPv6 addresses from an interface that loses carrier unless keep_addr_on_down is set — so an address added without it disappears before the agent ever starts. nodad is needed for the same reason: duplicate address detection cannot finish without a carrier, and the address would sit there tentative and unusable.

user ab is the point: the interface is persistent and owned by that user, so tsunagi up afterwards opens it with no privileges and no capabilities at all. The interface name and address are derived, so they are stable — the setup survives restarts and only has to be redone if the network name, the secret or this agent's WireGuard key changes.

Other ways, and their trade-offs:

approach	agent runs as	notes
tsunagi tun-setup (above)	ordinary user, no capabilities	recommended
sudo setcap cap_net_admin+ep ./tsunagi	ordinary user, one capability	the agent can then create the interface itself, but still cannot assign the IPv6 address (see below), so the ip -6 address add line is needed anyway. The capability is lost on every rebuild or copy.
systemd service	User=, AmbientCapabilities=CAP_NET_ADMIN	same caveat about the address
plain sudo tsunagi up	root	everything works, nothing is isolated

Known limitation. The agent cannot assign the IPv6 overlay address itself: the tun crate sets addresses through an IPv4-only ioctl, so an IPv6 address has to come from ip -6 address add or an equivalent. Rather than start with an interface that could never receive anything, the agent checks for the address in /proc/net/if_inet6 and refuses with the exact command to run. Doing it in-process would mean talking netlink directly, which is possible but not implemented.

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.