tun2proxy

A tunnel interface for HTTP and SOCKS proxies on Linux based on smoltcp.

Build

Clone the repository and cd into the project folder. Then run the following:

cargo build --release

Setup

Automated Setup

Using --setup auto, you can have tun2proxy configure your system to automatically route all traffic through the specified proxy. This requires running the tool as root and will roughly perform the steps outlined in the section describing the manual setup, except that a bind mount is used to overlay the /etc/resolv.conf file.

You would then run the tool as follows:

sudo ./target/release/tun2proxy --setup auto --proxy "socks5://1.2.3.4:1080"

Apart from SOCKS5, SOCKS4 and HTTP are supported.

Note that if your proxy is a non-global IP address (e.g. because the proxy is provided by some tunneling tool running locally), you will additionally need to provide the public IP address of the server through which the traffic is actually tunneled. In such a case, the tool will tell you to specify the address through --setup-ip <address> if you wish to make use of the automated setup feature.

Manual Setup

A standard setup, which would route all traffic from your system through the tunnel interface, could look as follows:

# The proxy type can be either SOCKS4, SOCKS5 or HTTP.
PROXY_TYPE=SOCKS5
PROXY_IP=1.2.3.4
PROXY_PORT=1080

# Create a tunnel interface named tun0 which your user can bind to,
# so we don't need to run tun2proxy as root.
sudo ip tuntap add name tun0 mode tun user $USER
sudo ip link set tun0 up

# To prevent a routing loop, we add a route to the proxy server that behaves
# like the default route.
sudo ip route add "$PROXY_IP" $(ip route | grep '^default' | cut -d ' ' -f 2-)

# Route all your traffic through tun0 without interfering with the default route.
sudo ip route add 128.0.0.0/1 dev tun0
sudo ip route add 0.0.0.0/1 dev tun0

# If you wish to also route IPv6 traffic through the proxy, these two commands will do.
sudo ip route add ::/1 dev tun0
sudo ip route add 8000::/1 dev tun0

# Make sure that DNS queries are routed through the tunnel.
sudo sh -c "echo nameserver 198.18.0.1 > /etc/resolv.conf"

./target/release/tun2proxy --tun tun0 --proxy "$PROXY_TYPE://$PROXY_IP:$PROXY_PORT"

Note that if you paste these commands into a shell script, which you then run with sudo, you might want to replace $USER with $SUDO_USER.

This tool implements a virtual DNS feature that is used by default. When a DNS packet to port 53 is detected, an IP address from 198.18.0.0/15 is chosen and mapped to the query name. Connections destined for an IP address from that range will supply the proxy with the mapped query name instead of the IP address. Since many proxies do not support UDP, this enables an out-of-the-box experience in most cases, without relying on third-party resolvers or applications. Depending on your use case, you may want to disable this feature using --dns none. In that case, you might need an additional tool like dnsproxy that is configured to listen on a local UDP port and communicates with a third-party upstream DNS server via TCP.

When you terminate this program and want to eliminate the impact caused by the above several commands, you can execute the following command. The routes will be automatically deleted with the tunnel device.

sudo ip link del tun0

CLI

Tunnel interface to proxy.

Usage: tun2proxy [OPTIONS] --proxy <URL>

Options:
  -t, --tun <name>      Name of the tun interface [default: tun0]
  -p, --proxy <URL>     Proxy URL in the form proto://[username[:password]@]host:port
  -d, --dns <method>    DNS handling [default: virtual] [possible values: virtual, none]
  -s, --setup <method>  Routing and system setup [possible values: auto]
      --setup-ip <IP>   Public proxy IP used in routing setup
  -h, --help            Print help
  -V, --version         Print version

Currently, tun2proxy supports HTTP, SOCKS4/SOCKS4a and SOCKS5. A proxy is supplied to the --proxy argument in the URL format. For example, an HTTP proxy at 1.2.3.4:3128 with a username of john.doe and a password of secret is supplied as --proxy http://john.doe:secret@1.2.3.4:3128. This works analogously to curl's --proxy argument.

Configuration Tips

DNS

When DNS resolution is performed by a service on your machine or through a server in your local network, DNS resolution will not be performed through the tunnel interface, since the routes to localhost or your local network are more specific than 0.0.0.0/1 and 128.0.0.0/1. In this case, it may be advisable to update your /etc/resolv.conf file to use a nameserver address that is routed through the tunnel interface. When virtual DNS is working correctly, you will see log messages like DNS query: example.org for hostnames which your machine is connecting to after having resolved them through DNS.

Note that software like the NetworkManager may change the /etc/resolv.conf file automatically at any time, which will result in DNS leaks. A hacky solution to prevent this consists in making the file immutable as follows: sudo chattr +i "$(realpath /etc/resolv.conf)".

IPv6

Some proxy servers might not support IPv6. When using virtual DNS, this is not a problem as DNS names are resolved by the proxy server. When DNS names are resolved to IPv6 addresses locally, this becomes a problem as the proxy will be asked to open connections to IPv6 destinations. In such a case, you can disable IPv6 on your machine. This can be done either through sysctl -w net.ipv6.conf.all.disable_ipv6=1 and sysctl -w net.ipv6.conf.default.disable_ipv6=1 or through ip -6 route del default, which causes the libc resolver (and other software) to not issue DNS AAAA requests for IPv6 addresses.

TODO

• Increase error robustness (reduce unwrap and expect usage)
• UDP support for SOCKS
• Native support for proxying DNS over TCP or TLS