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UDP virtual private tunnel daemon

Introduction

This repository contains a simple implementation of a point-to-point virtual private network by opening a TUN device and transferring raw traffic over UDP. This VPN was designed to create a tunnel between two hosts:

  1. A client host operating behind an obtrusive NAT which drops TCP connections frequently, but happens to pass UDP traffic reliably.
  2. A server host that is internet-accessible.

TUN traffic is sent ad-verbatim between the two endpoints via unencrypted UDP packets. Thus, this should only be used if a more secure protocol (like SSH; see github.com/dsnet/sshtunnel) is running on top of this VPN. In order to prevent attackers from connecting to other locally binded sockets on the endpoints, a simple port filter is built-in to restrict IP traffic to only the specified ports. Users of udptunnel should also setup iptable rules as a secondary measure to restrict malicious traffic.

This only supports Linux.

Usage

Build the daemon:

go get -u github.com/dsnet/udptunnel

Create a server configuration file:

{
	"TunnelAddress": "10.0.0.1",
	"NetworkAddress": ":8000",
	"AllowedPorts": [22],
}

The NetworkAddress with an empty host indicates that the daemon is operating in server mode.

Create a client configuration file:

{
	"TunnelAddress": "10.0.0.2",
	"NetworkAddress": "server.example.com:8000",
	"AllowedPorts": [22],
}

The host server.example.com is assumed to resolve to some address where the client can reach the server.

Start the daemon on both the client and server (assuming $GOPATH/bin is in your $PATH):

root@server.example.com $ udptunnel /path/to/config.json
root@client.example.com $ udptunnel /path/to/config.json

Try accessing the other endpoint (example is for client to server):

user@client.example.com $ ping 10.0.0.1
PING 10.0.0.1 (10.0.0.1) 56(84) bytes of data.
64 bytes from 10.0.0.1: icmp_req=1 ttl=64 time=56.7 ms
64 bytes from 10.0.0.1: icmp_req=2 ttl=64 time=58.7 ms
64 bytes from 10.0.0.1: icmp_req=3 ttl=64 time=50.1 ms
64 bytes from 10.0.0.1: icmp_req=4 ttl=64 time=51.6 ms


user@client.example.com $ nmap 10.0.0.1
Host is up (0.063s latency).
PORT   STATE SERVICE
22/tcp open  ssh


user@client.example.com $ ssh 10.0.0.1
Password: ...

The above example shows the client trying to communicate with the server, which is addressable at 10.0.0.1. The example commands can be done from the server by dialing the client at 10.0.0.2, instead.