Langue: en

Version: JUL 2008 (ubuntu - 25/10/10)

Section: 8 (Commandes administrateur)


iodine, iodined - tunnel IPv4 over DNS


iodine [-v]

iodine [-h]

iodine [-f] [-u user ] [-P password ] [-m fragsize ] [-t chrootdir ] [-d device ] [-m fragsize ] [ nameserver ] topdomain

iodined [-v]

iodined [-h]

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.


Common Options:

Print version info and exit.
Print usage info and exit.
Keep running in foreground.
-u user
Drop privileges and run as user 'user' after setting up tunnel.
-t chrootdir
Chroot to 'chrootdir' after setting up tunnel.
-d device
Use the TUN device 'device' instead of the normal one, which is dnsX on Linux and otherwise tunX.
-P password
Use 'password' to authenticate. If not used, stdin will be used as input. Only the first 32 characters will be used.

Client Options:

-m fragsize
Maximum downstream fragsize. Not setting this will cause the client to probe the maximum accepted downstream packet size.

Server Options:

Disable checks on client IP on all incoming requests.
Don't try to configure IP address or MTU. This should only be used if you have already configured the device that will be used.
Increase debug level. Level 1 prints info about each RX/TX packet.
-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.
-l listen_ip
Make the server listen only on 'listen_ip' instead of on for incoming connections.
-p port
Make the server listen on 'port' instead of 53 for traffic. Note: You must make sure the dns requests are forwarded to this port yourself.
-n external ip
The IP address to return in NS responses. Default is to return the address used as destination in the query.
-b dnsport
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.

Client Arguments:

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 file.
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.

Server Arguments:

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 or ranges. The default netmask is /27, can be overridden by specifying it here. Using a smaller network will limit the number of concurrent users.
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 test.asdf
(If you already use the network, use another internal net like
- Enter a password
- On the client, run: ./iodine -f test.asdf
(Replace with the server's ip address)
- Enter the same password
- Now the client has the tunnel ip and the server has
- Try pinging each other through the tunnel
- Done! :)
To actually use it through a relaying nameserver, see below.

Full setup:

Server side:
To use this tunnel, you need control over a real domain (like, 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, to the server. If you use BIND for the domain, add these lines to the zone file (replace with your server ip):
 tunnel1host     IN      A
 tunnel1         IN      NS

Now any DNS querys for domains ending with will be sent to your server. Start iodined on the server. The first argument is the tunnel IP address (like and the second is the assigned domain (in this case 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 ( If DNS queries are allowed to any computer, you can use the tunnel endpoint (example: or as the first argument. The tunnel interface will get an IP close to the servers (in this case 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.
MTU issues:
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


Erik Ekman <> and Bjorn Andersson <>