This is a simple tunnelling program written to test tunnelling of IPv4 and IPv6 over IPv4 or IPv6. It can use TCP or UDP as underlying protocol over which tunnelling happens. It can also create a persistent tun device and set its owner.

The program uses multithreading (pthread) to read and write between two devices (tun and network). Although the code is written by me, I have referred to and am influenced by article and code snippets on http://backreference.org/2010/03/26/tuntap-interface-tutorial/

Copyright (C) 2013 Aniket Oak

This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version.

This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details.

You should have received a copy of the GNU General Public License along with this program. If not, see http://www.gnu.org/licenses/.

This program operates in three modes, the 'make' mode is for creation of tun device and setting its owner to specific user. This tun device can be then used by subsequent invokations for tunnelling.

The 'tunnelling' mode has two modes of operation viz. server and client. The client connects to the server program on remote machine using TCP or UDP over the network. Then the client and servers read the data from tun device and write it on network and read data from network and write it on tun device.

This creates a tunnel between the two tun devices which can be used by other programs. Here is a snippet how it can be used.

# local machine (where client runs)

$ ifconfig
tun3      Link encap:UNSPEC  HWaddr 00-00-00-00-00-00-00-00-00-00-00-00-00-00-00-00  
inet6 addr: aaaa::bbba/112 Scope:Global
UP POINTOPOINT RUNNING NOARP MULTICAST  MTU:1500  Metric:1


# remote machine (where server runs)
$ ifconfig 
tun3      Link encap:UNSPEC  HWaddr 00-00-00-00-00-00-00-00-00-00-00-00-00-00-00-00  
inet6 addr: aaaa::bbbb/112 Scope:Global
UP POINTOPOINT RUNNING NOARP MULTICAST  MTU:1500  Metric:1


# local machine
$ ping6 aaaa::bbbb
PING aaaa::bbbb(aaaa::bbbb) 56 data bytes
64 bytes from aaaa::bbbb: icmp_seq=1 ttl=64 time=1.12 ms
64 bytes from aaaa::bbbb: icmp_seq=2 ttl=64 time=0.159 ms
64 bytes from aaaa::bbbb: icmp_seq=3 ttl=64 time=0.138 ms
64 bytes from aaaa::bbbb: icmp_seq=4 ttl=64 time=0.139 ms
^C
--- aaaa::bbbb ping statistics ---
4 packets transmitted, 4 received, 0% packet loss, time 3971ms
rtt min/avg/max/mdev = 0.138/0.391/1.129/0.426 ms
$ 

For creation of the tun device, the same program can be used as follows:

$ sudo ./simple-tun -m m -e -d tun5 -u aniket -i 100.100.0.1/24
Created tun device(3): tun5
tun device: tun5, uid: 1000, gid: 1000, persistence: 1

This will create a tun device which can be then used for tunnelling. Note that for this version, a tun device ipv6 address needs to be setup using following commands.

# ip link set
# ip addr add

The program cannot add and set ipv6 addresses for you (yet).

Usage of the program is as follows:

simple-tun - v2.1

Usage: simple-tun -m [mode] -d [device name] -p [port] -o [underlying prot] -s [server] -v 
				  -m [mode] -d [device name] -e -u [user]
where,
	-m: mode        : either of 's' or 'c' signifying whether to act as client or server while tunnelling,
						OR
					  can be 'm' which tells the program that it is supposed to create new tun device.
	-d: device name : tun device name
	-p: port        : port number used by client and server for tunnelling (for listening in case of server).
					  only significant in case mode isn't 'm'
	-o: protocol    : name of the underlying protocol over which tunneling happens. can be 'tcp' or 'udp'
					  only significant in case mode isn't 'm'
	-t: ip version	: version of ip protocol to be used in tunnel. Can be 'ipv4' or 'ipv6'
					  only significant in case mode isn't 'm'
	-s: server name : name or ip address of the server. (Only considered in case of client)
					  only significant in case mode isn't 'm'
	-e: persistence : Whether to set device persistent or not
					  only significant in case mode is 'm'
	-u: user        : User to set as owner of the device
					  only significant in case mode is 'm'
	-i: ip address  : Dotted decimal ipv4 address with possibly mask in CDIR notation to be set as address
					  and mask of tun device. only significant in case mode is 'm'
	-v: verbose     : print the info messages which may slow down the performance
	-h: help        : print this usage

1. Simple single threaded program
2. Addition of verbosity flag to avoid printing debug messages (perf issue)
3. Added functionality to create persistent tun device and set owner removing the need to tool like openvpn to do the same
4. Multi-threading to handle read/writes between the devices faster
5. Added logic to avoid copying buffer between two threads
6. Changed threading architecture to avoid using queues between two threads (perf issue).
7. Added support to add ipv4 address and mask and set the link up and running.
8. Added support for tunnelling over ipv6 network connection