iodine, iodined - tunnel IPv4 over DNS
iodine [-f] [-u user ] [-P password ] [-m fragsize ] [-t chrootdir ]
[-d device ] [-m fragsize ] [ nameserver ] topdomain
iodined [-c] [-s] [-f] [-D] [-u user ] [-t chrootdir ] [-d device ] [-m
mtu ] [-l listen_ip ] [-p port ] [-n external ip ] [-b dnsport ] [-P
password ] tunnel_ip [ /netmask ] topdomain
iodine lets you tunnel IPv4 data through a DNS server. This can be
useful in situations where Internet access is firewalled, but DNS
queries are allowed. It needs a TUN/TAP device to operate. The
bandwidth is asymmetrical with limited upstream and up to 1 Mbit/s
downstream. iodine is the client application, iodined is the server.
-v Print version info and exit.
-h Print usage info and exit.
-f Keep running in foreground.
Drop privileges and run as user ’user’ after setting up tunnel.
Chroot to ’chrootdir’ after setting up tunnel.
Use the TUN device ’device’ instead of the normal one, which is
dnsX on Linux and otherwise tunX.
Use ’password’ to authenticate. If not used, stdin will be used
as input. Only the first 32 characters will be used.
Maximum downstream fragsize. Not setting this will cause the
client to probe the maximum accepted downstream packet size.
-c Disable checks on client IP on all incoming requests.
-s Don’t try to configure IP address or MTU. This should only be
used if you have already configured the device that will be
-D Increase debug level. Level 1 prints info about each RX/TX
-m mtu Set ’mtu’ as mtu size for the tunnel device. This will be sent
to the client on connect, and the client will use the same mtu.
Make the server listen only on ’listen_ip’ instead of on 0.0.0.0
for incoming connections.
Make the server listen on ’port’ instead of 53 for traffic.
Note: You must make sure the dns requests are forwarded to this
-n external ip
The IP address to return in NS responses. Default is to return
the address used as destination in the query.
If this port is specified, all incoming requests not inside the
tunnel domain will be forwarded to this port on localhost, to be
handled by a real dns.
The nameserver to use to relay the dns traffic. This can be any
relaying nameserver or the ip number of the server running
iodined if reachable. This argument is optional, and if not
specified a nameserver will be read from the /etc/resolv.conf
The dns traffic will be sent as querys of type NULL for
subdomains under ´topdomain’. This is normally a subdomain to a
domain you own. Use a short domain name to get better
throughput. If nameserver is the iodined server, then the
topdomain can be chosen freely. This argument must be the same
on both the client and the server.
This is the servers ip address on the tunnel interface. The
client will be given the next ip number in the range. It is
recommended to use the 10.0.0.0 or 172.16.0.0 ranges. The
default netmask is /27, can be overridden by specifying it here.
Using a smaller network will limit the number of concurrent
The dns traffic will is expected to be sent as querys of type
NULL for subdomains under ’topdomain’. This is normally a
subdomain to a domain you own. Use a short domain name to get
better throughput. This argument must be the same on both the
client and the server.
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.
To use this tunnel, you need control over a real domain (like
mytunnel.com), and a server with a public IP number. If the
server already runs a DNS server, change the listening port and
then use the -b option to let iodined forward the DNS requests.
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 (replace 10.15.213.99 with your server ip):
tunnel1host IN A 10.15.213.99
tunnel1 IN NS tunnel1host.mytunnel.com.
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.
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.
The normal case is to route all traffic through the DNS tunnel.
To do this, first add a route to the nameserver you use with the
default gateway as gateway. Then replace the default gateway
with the servers IP address within the DNS tunnel, and configure
the server to do NAT.
These issues should be solved now, with automatic fragmentation
of downstream packets. There should be no need to set the MTU
explicitly on the server.
File bugs at http://dev.kryo.se/iodine/
Erik Ekman <firstname.lastname@example.org> and Bjorn Andersson <email@example.com>