iodine - http://code.kryo.se/iodine

***********************************

This is a piece of software that lets you tunnel IPv4 data through a DNS
server. This can be usable in different situations where internet access is
firewalled, but DNS queries are allowed.


QUICKSTART:

Try it out within your own LAN! Follow these simple steps:
- On your server, run: ./iodined -f 10.0.0.1 test.asdf
  (If you already use the 10.0.0.0 network, use another internal net like 
  172.16.0.0)
- Enter a password
- On the client, run: ./iodine -f 192.168.0.1 test.asdf
  (Replace 192.168.0.1 with the server's ip address)
- Enter the same password
- Now the client has the tunnel ip 10.0.0.2 and the server has 10.0.0.1
- Try pinging each other through the tunnel
- Done! :)
To actually use it through a relaying nameserver, see below.


HOW TO USE:

Server side:
To use this tunnel, you need control over a real domain (like mytunnel.com),
and a server with a static public IP number (not behind NAT) that does not 
yet run a DNS server. Then, delegate a subdomain (say, tunnel1.mytunnel.com)
to the server. If you use BIND for the domain, add these lines to the zone file:

tunnel1host	IN	A	10.15.213.99
tunnel1		IN	NS	tunnel1host.mytunnel.com.

Do not use CNAME instead of A above.
Now any DNS querys for domains ending with tunnel1.mytunnnel.com will be sent
to your server. Start iodined on the server. The first argument is the tunnel
IP address (like 192.168.99.1) and the second is the assigned domain (in this
case tunnel1.mytunnel.com). The -f argument will keep iodined running in the
foreground, which helps when testing. iodined will start a virtual interface,
and also start listening for DNS queries on UDP port 53. Either enter a
password on the commandline (-P pass) or after the server has started. Now 
everything is ready for the client.

Client side: 
All the setup is done, just start iodine. It also takes two
arguments, the first is the local relaying DNS server and the second is the
domain used (tunnel1.mytunnnel.com). If DNS queries are allowed to any
computer, you can use the tunnel endpoint (example: 10.15.213.99 or
tunnel1host.mytunnel.com) as the first argument. The tunnel interface will get
an IP close to the servers (in this case 192.168.99.2) and a suitable MTU. 
Enter the same password as on the server either by argument or after the client
has started. Now you should be able to ping the other end of the tunnel from 
either side.  


MISC. INFO:

Try experimenting with the MTU size (-m option) to get maximum bandwidth. It is
set to 1024 by default, which seems to work with most DNS servers. If you have
problems, try setting it to 220 as this ensures all packets to be < 512 bytes.
Some DNS servers enforce a 512 byte packet limit, and this is probably the case
if you can ping through the tunnel but not login via SSH.

If you have problems, try inspecting the traffic with network monitoring tools
and make sure that the relaying DNS server has not cached the response. A
cached error message could mean that you started the client before the server.

The upstream data is sent gzipped encoded with Base32. DNS protocol allows
one query per packet, and one query can be max 256 chars. Each domain name part
can be max 63 chars. So your domain name and subdomain should be as short as
possible to allow maximum throughput.


TIPS & TRICKS:

If your port 53 is taken on a specific interface by an application that does 
not use it, use -p on iodined to specify an alternate port (like -p 5353) and 
use for instance iptables (on Linux) to forward the traffic:
iptables -t nat -A PREROUTING -i eth0 -p udp --dport 53 -j DNAT --to :5353
(Sent in by Tom Schouten)


PORTABILITY:

iodine has been tested on Linux (arm, ia64, x86, AMD64 and SPARC64), FreeBSD 
(ia64, x86), OpenBSD (x86), NetBSD (x86) and MacOS X (10.3, ppc, with 
http://www-user.rhrk.uni-kl.de/~nissler/tuntap/). It should work on other 
unix-like systems as well that has TUN/TAP tunneling support (after some 
patching). Let us know if you get it to run on other platforms. 


THE NAME:

The name iodine was chosen since it starts with IOD (IP Over DNS) and since
iodine has atomic number 53, which happens to be the DNS port number.


THANKS:

- To kuxien for FreeBSD and OS X testing
- To poplix for code audit


AUTHORS & LICENSE:

Copyright (c) 2006-2007 Bjorn Andersson <flex@kryo.se>, Erik Ekman <yarrick@kryo.se>

Permission to use, copy, modify, and distribute this software for any purpose
with or without fee is hereby granted, provided that the above copyright notice
and this permission notice appear in all copies.

THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES WITH
REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY AND
FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT,
INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM
LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR
OTHER TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR
PERFORMANCE OF THIS SOFTWARE.


MD5 implementation by L. Peter Deutsch (license and source in src/md5.[ch])
Copyright (C) 1999, 2000, 2002 Aladdin Enterprises.  All rights reserved.