Secured network tunnel for connecting two computers. Main usage: connecting travelling computer to one server.

• Works for Windows 7 or greater
• Client-Server model
• Works on IP level and tunnels ICMP, TCP and UDP data
• Uses only one UDP port (12017 by default)
• Can connect by hostnames with periodic refreshing data
• Client can be NAT'ed
• Server can be NAT'ed, but you need to use a special proxy
• Creates transparent secured tunnel between two computers without allocation of additional IP-addresses, so you do not need for separate DNS-names for computers

• No server needed
• No separate IP address or network interface
• Always active (if service running)

• No need to specify both endpoints to static addresses
• Only one UDP port for usage (instead of ESP, AH protocols and 500 and 4500 UDP ports)
• Just some settings to make tunnel works, you no need to specify lot of parameters in different configs and phases
• Currently, no IPv6 support

• Due usage existing IPs for computers there are can be collision with current IPs
• If network has problems with UDP fragmentation (or badly configured Jumbo Frames), there are can be strange errors and packet loss

AutoTunnel uses WinDivert library to catch outgoing network packets, transfers it to another computer and puts them back, as normal packets. So, this packets looks like usual network packets, but you do not need to specify routing tables between computers. These computers are in virtual local network. After establishing connection with another computer, it begins to catch packets to source computer and transfers it back to it through established tunnel.

Tunnel is encrypted with AES256 with PFS support. Currently, for auth you can use only preshared keys (I think, it simple and good variant for authentication, because one key can be changed to another in some seconds, you do not need to regenerate certificates or private keys). This key is used only for initial handshake and has not transferred in open form. After handshake stage, another, temporary session key is used for data encryption.

There are two types of computers:

• Server - listens incoming connections
• Client - connects to server

Any computer can be server for others computers and client for another. There is no need to use separate program. So, despite only two computers can use one tunnel, you can create a lot of tunnels between pairs of different computers.

Also, you can establish connection between two computers in client mode. Two tunnels will be created, but packets will be passed correctly.

You need:

• Windows 7/2008R2 or greater
• Enabled .NET Framework 4.0
• VC Redist 2012

Program can be started in console or work as a service. Service can be installed in next way:

AutoTunnel.exe service install
sc start AutoTunnel

Before starting, you need to configure config.json file. Example config:

{
	"enableListening": true,
	"addFirewallRule": true,
	"port": 12017,
	"logFileName": "somelog.log",
	"autoReloadOnChange": true,
	"remoteClients": [
		{
			"key": "key1",
			"description": "my key"
		}
	],
	"remoteServers": [
		{
			"tunnelHost": "192.168.16.8",
			"connectHost": "192.168.18.1:12017",
			"proxyHost": "192.168.24.1:12018",
			"key": "key1",
			"keepAlive": true,
			"connectOnStart": true
		}
	]
}

If target computer is unavailable from outer network but you have separate computer which can transfer packets from local network to outer network, you can use special proxy program.

Full scheme of connection can be similar:

Client computer (gray ip, NAT) <-> Router <-> (Internet) <-> Router     <-> Proxy       <-> Server (NAT)
192.168.1.42 <-> 192.168.1.1|91.10.20.42  <-> (Internet) <-> 82.40.10.1 <-> 82.40.10.54 <-> 10.0.1.15

Current implementation does not encrypt data, it just transfer packets from one computer to another. For better compatibility, current version of proxy is written on node.js, so it can be run at lot of hardware.

Also, when you use a proxy, just proxy resolves host name to ip. So, it can be useful for internal host names.

By default, proxy is listening on 12018 port and can filter destination ip addresses or host names.

AutoTunnel has MIT license, but it uses WinDivert library with LGPL3 license.