Rusnel

Description

Rusnel is a fast TCP/UDP tunnel, transported over and encrypted using QUIC protocol. Single executable including both client and server. Written in Rust.

Quickstart

cargo install rusnel

# on your public box
rusnel server --tls-self-signed
# server cert fingerprint: sha256:abcd...

# on your laptop — expose laptop:8080 as <server>:8080
rusnel client --tls-fingerprint sha256:abcd... <server>:8080 R:8080

Features

• Easy to use
• Single executable including both client and server.
• Uses QUIC protocol for fast and multiplexed communication.
• Encrypted connections using the QUIC protocol (TLS 1.3).
• Static forward tunneling (TCP, UDP)
• Static reverse tunneling (TCP, UDP)
• Dynamic tunneling (socks5, including UDP ASSOCIATE)
• Dynamic reverse tunneling (reverse socks5, including UDP ASSOCIATE)
• Layered peer authentication: insecure, fingerprint pinning, or full mTLS (see Authentication).

Install

cargo install rusnel

Or build from source:

git clone https://github.com/guyte149/Rusnel.git
cd Rusnel
cargo build --release

Pre-built binaries for Linux (x86_64 + aarch64, gnu and musl) and macOS (x86_64 + Apple Silicon) are attached to each GitHub release. Windows is not yet supported (the admin API is Unix-socket-only).

Docker

Multi-arch images (linux/amd64, linux/arm64) are published to GHCR:

docker pull ghcr.io/guyte149/rusnel:latest
docker run --rm -p 8080:8080/udp ghcr.io/guyte149/rusnel \
    server --tls-self-signed

Note that QUIC runs over UDP — -p 8080:8080/udp, not /tcp.

Usage

$ rusnel --help
A fast tcp/udp tunnel

Usage: rusnel <COMMAND>

Commands:
  server  run Rusnel in server mode
  client  run Rusnel in client mode
  cert    generate certificates for use with --tls-* flags
  help    Print this message or the help of the given subcommand(s)

Options:
  -h, --help     Print help
  -V, --version  Print version

$ rusnel server --help
run Rusnel in server mode

Usage: rusnel server [OPTIONS]

Options:
      --host <HOST>          defines Rusnel listening host [default: 0.0.0.0]
  -p, --port <PORT>          defines Rusnel listening port [default: 8080]
      --allow-reverse        Allow clients to specify reverse port forwarding remotes
      --allow-socks          Allow clients to specify SOCKS5 remotes. `R:socks`
                             additionally requires `--allow-reverse`.
      --insecure             Disable all TLS authentication (testing only)
      --tls-self-signed      Persisted self-signed cert under --tls-state-dir
      --tls-state-dir <DIR>  Directory for persisted self-signed cert/key (default: ~/.rusnel)
      --tls-cert <PATH>      Server PEM cert (paired with --tls-key)
      --tls-key  <PATH>      Server PEM key  (paired with --tls-cert)
      --tls-ca   <PATH>      Enable mTLS: require client certs signed by this CA
      --congestion <CC>      QUIC congestion controller: cubic (default) or bbr.
                             cubic wins on loopback / clean LANs; bbr wins on
                             high-BDP / lossy WAN links (≳25ms RTT or any loss).
  -v, --verbose              enable verbose logging
      --debug                enable debug logging
  -h, --help                 Print help

$ rusnel client --help
run Rusnel in client mode

Usage: rusnel client [OPTIONS] <SERVER> <remote>...

Arguments:
  <SERVER>     defines the Rusnel server address (in form of host:port)
  <remote>...
               <remote>s are remote connections tunneled through the server, each which come in the form:

                   <local-host>:<local-port>:<remote-host>:<remote-port>/<protocol>

                   ■ local-host defaults to 0.0.0.0 (all interfaces).
                   ■ local-port defaults to remote-port.
                   ■ remote-port is required*.
                   ■ remote-host defaults to 0.0.0.0 (server localhost).
                   ■ protocol defaults to tcp.

               which shares <remote-host>:<remote-port> from the server to the client as <local-host>:<local-port>, or:

                   R:<local-host>:<local-port>:<remote-host>:<remote-port>/<protocol>

               which does reverse port forwarding,
               sharing <remote-host>:<remote-port> from the client to the server\'s <local-host>:<local-port>.

                   example remotes

                       1337
                       example.com:1337
                       1337:google.com:80
                       192.168.1.14:5000:google.com:80
                       socks
                       5000:socks
                       R:2222:localhost:22
                       R:socks
                       R:5000:socks
                       1.1.1.1:53/udp
                       [::1]:80
                       [::1]:5000:[2001:db8::1]:80
                       R:[::1]:2222:[::1]:22
                       stdio:example.com:22

                   IPv6 literals must be wrapped in [brackets] (same
                   convention as URLs and ssh -L).

                   When the Rusnel server has --allow-reverse enabled, remotes can be prefixed with R to denote that they are reversed.

                   Remotes can specify "socks" in place of remote-host and remote-port.
                   The default local host and port for a "socks" remote is 127.0.0.1:1080.

                   Remotes can specify "stdio" in place of <local-host>:<local-port>
                   to pipe the client process's stdin/stdout to/from the tunnel
                   instead of binding a local listener. Stdio remotes are
                   forward-only.


Options:
      --insecure                  Skip server cert verification (testing only)
      --tls-fingerprint <SHA256>  Pin server cert by SHA-256 fingerprint
      --tls-ca <PATH>             Verify server cert against this CA bundle
      --tls-cert <PATH>           Client PEM cert (mTLS; paired with --tls-key + --tls-ca)
      --tls-key  <PATH>           Client PEM key  (mTLS; paired with --tls-cert + --tls-ca)
      --tls-server-name <NAME>    Override SNI / verification name
      --congestion <CC>           QUIC congestion controller: cubic (default) or
                                  bbr. cubic wins on loopback / clean LANs; bbr
                                  wins on high-BDP / lossy WAN links.
      --max-retry-count <N>       Reconnect attempts after a disconnect or
                                  failed connect. -1 = retry forever (default);
                                  counter resets on every successful connect.
      --max-retry-interval <S>    Cap on the exponential reconnect backoff
                                  (default 300s; starts at 200 ms and doubles).
      --proxy <URL>               Route the QUIC connection through a SOCKS5
                                  proxy via UDP ASSOCIATE.
                                  Form: socks5://[user:pass@]host:port.
  -v, --verbose                   enable verbose logging
      --debug                     enable debug logging
  -h, --help                      Print help

The client survives both transient network drops and full server restarts out of the box: on disconnect it logs the close reason (e.g. closed by peer: server received ^C (code 0)), backs off, and tries every resolved address in parallel using RFC 8305 Happy Eyeballs so v4-only servers reachable via a v6-preferring resolver still connect within ~250 ms. Server-side resources (including reverse-tunnel listeners) are released the moment the QUIC connection drops.

Authentication

Both the server and the client require an explicit TLS-mode flag — there is no silent insecure default. Three modes:

Quickest path for a private/single-user setup — the server logs its fingerprint at startup, the client pins it:

rusnel server --tls-self-signed
# server cert fingerprint: sha256:abcd...
rusnel client --tls-fingerprint sha256:abcd... 1.2.3.4:8080 1337

For full mTLS, generate a CA + server + client cert (no openssl required):

scripts/gen-certs.sh ./pki 1.2.3.4
rusnel server --tls-ca   ./pki/ca.pem --tls-cert ./pki/server.pem --tls-key ./pki/server.key
rusnel client --tls-ca   ./pki/ca.pem --tls-cert ./pki/client.pem --tls-key ./pki/client.key \
              --tls-server-name 1.2.3.4 1.2.3.4:8080 1337

rusnel cert --help lists the underlying subcommands (ca, server, client, fingerprint) for finer control.

Embedded credentials (drop-and-run binaries)

Rusnel can bake credentials and the default invocation into the binary at build time via RUSNEL_EMBED_* env vars. The resulting binary connects, authenticates, and starts forwarding the moment it's run — no flags, no subcommand, no config file. CLI flags still override embedded values, so --help and ad-hoc subcommands keep working.

RUSNEL_EMBED_CA=./pki/ca.pem \
RUSNEL_EMBED_CLIENT_CERT=./pki/client.pem \
RUSNEL_EMBED_CLIENT_KEY=./pki/client.key \
RUSNEL_EMBED_SERVER_NAME=1.2.3.4 \
RUSNEL_EMBED_ARGS='client 1.2.3.4:8080 R:2222:localhost:22' \
cargo build --release
./target/release/rusnel               # connects + opens reverse tunnel

Recognised vars: RUSNEL_EMBED_ARGS, RUSNEL_EMBED_SERVER_ADDR, RUSNEL_EMBED_FINGERPRINT, RUSNEL_EMBED_SERVER_NAME, RUSNEL_EMBED_CA, RUSNEL_EMBED_SERVER_CERT, RUSNEL_EMBED_SERVER_KEY, RUSNEL_EMBED_CLIENT_CERT, RUSNEL_EMBED_CLIENT_KEY. See build.rs for the full mapping.

Configuration file

Both rusnel server and rusnel client accept --config <PATH> pointing at a TOML file. A single file may contain a [server] section, a [client] section, or both — only the section matching the subcommand is read. Unknown keys are rejected so typos surface immediately.

Precedence: CLI flag > config file > built-in default. Any flag you pass on the command line overrides whatever the file says.

The TLS-mode flags are special: passing any of --insecure, --tls-self-signed, --tls-cert, --tls-key, --tls-ca (server) or --insecure, --tls-fingerprint, --tls-ca, --tls-cert, --tls-key (client) on the CLI causes all of the file's TLS-mode keys to be ignored — you get exactly the mode you typed, with no silent mixing.

A minimal server example:

[server]
host             = "0.0.0.0"
port             = 8080
allow_reverse    = true
allow_socks      = true
tls_self_signed  = true
log_format       = "json"

A minimal client example:

[client]
server  = "tunnel.example.com:8080"
remotes = ["R:2222:localhost:22", "1.1.1.1:53/udp"]
tls_fingerprint = "sha256:0123456789abcdef..."
max_retry_interval = 60

Both positional arguments (<server> and <remote>...) can be supplied either by the file or on the CLI; the CLI version wins when both are present.

A fully-annotated example covering every supported key lives at examples/rusnel.toml.

Logging

Rusnel uses tracing end-to-end with structured fields and stable span hierarchy.

Verbosity (mutually exclusive):

rusnel server ...                  # INFO  (default)
rusnel server -v ...               # DEBUG for rusnel modules
rusnel server --debug ...          # TRACE for rusnel modules
rusnel server -q / --quiet ...     # WARN-and-above only

For finer control set RUST_LOG directly — it overrides the flags:

RUST_LOG=rusnel=debug,quinn=info rusnel server ...
RUST_LOG=rusnel::common::tcp=trace rusnel client ...

Format: human-readable compact (default) or one JSON object per line for log aggregators:

rusnel server --log-format json ...

Logs go to stderr (so forward stdio: tunnels can use stdout cleanly). Timestamps are ISO-8601 UTC with millisecond precision; ANSI colours are auto-detected from the stderr TTY.

Every event is wrapped in spans whose field names match the rusnel ctl / admin-API ID schema (client_id, tunnel_id, conn_id, …), so logs grep cleanly against API output. Every conn emits a conn opened event on entry and a conn closed event on exit carrying bytes_in, bytes_out, and dur_ms.

Example session (compact format, ANSI stripped):

2026-05-05T11:03:55.022Z  INFO client: connected client_id=1 peer=127.0.0.1:62178
2026-05-05T11:03:55.027Z  INFO client: session established count=1
2026-05-05T11:03:55.027Z  INFO client: tunnel registered tunnel_id=1 dir="forward" spec=19999=>127.0.0.1:9999/tcp
2026-05-05T11:03:55.670Z  INFO conn: conn opened conn_id=1 tunnel_id=1 peer="127.0.0.1:9999"
2026-05-05T11:03:55.671Z  INFO conn: conn closed bytes_in=12 bytes_out=17 dur_ms=1

Server admin API & rusnel ctl

The server exposes a read-only admin HTTP API on a unix domain socket by default at ~/.rusnel/admin.sock (mode 0600). Filesystem permissions are the only auth — only the user that started the server can connect. Pass --admin-socket <path> to override the path or --no-admin-socket to disable.

Terminology: client, tunnel, conn

State is modelled in three layers, each with one meaning:

• A client is one connected rusnel client daemon. Lives for the lifetime of the QUIC connection.
• A tunnel is the remote declaration a client established with the server (R:5000=>socks, 1080=>1.1.1.1:53/udp, …). Deduplicated per client by spec; lives as long as the client.
• A conn is a single proxied network connection going through a tunnel — one accepted TCP connection, one per-source UDP flow, one SOCKS5 CONNECT, one SOCKS5 UDP target.

Query the API with rusnel ctl (or curl --unix-socket):

rusnel ctl clients                       # tab-aligned table by default
rusnel ctl client 3                      # client detail incl. its tunnels
rusnel ctl client-conns 3                # active conns across all of client 3's tunnels
rusnel ctl tunnels                       # every tunnel across every client
rusnel ctl tunnel 7                      # tunnel detail + its active conns
rusnel ctl tunnel-conns 7                # just the conns on tunnel 7
rusnel ctl conns --json                  # every active conn, raw JSON
rusnel ctl history --limit 20            # recent client disconnects

ctl defaults to the same socket path the server uses, so the zero-flag pairing just works.

The available endpoints (GET only in this release):

Write operations (kick client, kill conn), Prometheus /metrics, and an embedded web UI are tracked as phase-2 follow-ups in ROADMAP.md.

Performance

Rusnel (QUIC) vs Chisel (SSH-over-WebSocket) on loopback. Throughput is iperf3 over a tunneled TCP forward (100 MB × 5 runs + warmup, median); latency is the round-trip time of a 64 B echo across the tunnel.

End-to-end HTTP request times through the tunnel across payload sizes (median of 5 runs, error bars show min/max):

The benchmark harness also includes a wan profile that applies tc qdisc netem delay 25ms to the loopback interface to approximate a 50 ms-RTT WAN. Reproduce everything with ./benchmark/run.sh (requires Docker; needs --cap-add=NET_ADMIN for netem profiles, which the script adds for you). See benchmark/ for tunables.

Roadmap

Planned protocol features (HTTP/3 facade, 0-RTT resumption, NAT hole-punching), access-control work (server-side ACLs, OIDC client auth), and admin-API phase 2 (kick / kill / Prometheus / web UI) are tracked in ROADMAP.md. Contributions welcome.

License

Licensed under the Apache License 2.0.