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 a measured maximum of 680 kbit/s upstream and 2.3 Mbit/s
downstream in a wired LAN test network.
Realistic sustained throughput on a Wifi network using a carrier-grade
DNS cache has been measured at some 50 kbit/s upstream and over 200 kbit/s
is the client application,
is the server.
Note: server and client are required to speak the exact same protocol. In most
cases, this means running the same iodine version. Unfortunately, implementing
backward and forward protocol compatibility is usually not feasible.
Print version info and exit.
Print usage info and exit.
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,
will be used as input. Only the first 32 characters will be used.
Apply SELinux 'context' after initialization.
Create 'pidfile' and write process id in it.
Skip raw UDP mode. If not used, iodine will try getting the public IP address
of the iodined host and test if it is reachable directly. If it is, traffic
will be sent to the server instead of the DNS relay.
Force maximum downstream fragment size. Not setting this will cause the
client to automatically probe the maximum accepted downstream fragment size.
Maximum length of upstream hostnames, default 255.
Usable range ca. 100 to 255.
Use this option to scale back upstream bandwidth in favor of downstream
Also useful for DNS servers that perform unreliably when using full-length
hostnames, noticeable when fragment size autoprobe returns very
different results each time.
DNS request type override.
By default, autodetection will probe for working DNS request types, and
will select the request type that is expected to provide the most bandwidth.
However, it may turn out that a DNS relay imposes limits that skew the
picture, which may lead to an "unexpected" DNS request type providing
In that case, use this option to override the autodetection.
In (expected) decreasing bandwidth order, the supported DNS request types are:
may/will cause additional lookups by "smart" caching
nameservers to get an actual IP address, which may either slow down or fail
Force downstream encoding type for all query type responses except NULL.
Default is autodetected, but may not spot all problems for the more advanced
Use this option to override the autodetection.
is the lowest-grade codec and should always work; this is used when
provides more bandwidth, but may not work on all nameservers.
is equal to Base64 except in using underscore ('_')
instead of plus sign ('+'), possibly working where
uses high byte values (mostly accented letters in iso8859-1),
which might work with some nameservers.
For TXT queries,
will provide maximum performance, but this will only work if the nameserver
path is fully 8-bit-clean for responses that are assumed to be "legible text".
-L1 (default): Use lazy mode for improved performance and decreased latency.
A very small minority of DNS relays appears to be unable to handle the
lazy mode traffic pattern, resulting in no or very little data coming through.
The iodine client will detect this and try to switch back to legacy mode,
but this may not always work.
In these situations use -L0 to force running in legacy mode
Maximum interval between requests (pings) so that intermediate DNS
servers will not time out. Default is 4 in lazy mode, which will work
fine in most cases. When too many SERVFAIL errors occur, iodine
will automatically reduce this to 1.
To get absolute minimum DNS traffic,
increase well above 4, but not so high that SERVFAIL errors start to occur.
There are some DNS relays with very small timeouts,
notably dnsadvantage.com (ultradns), that will give
SERVFAIL errors even with -I1; data will still get trough,
and these errors can be ignored.
Maximum useful value is 59, since iodined will close a client's
connection after 60 seconds of inactivity.
Disable checking the client IP address on all incoming requests.
By default, requests originating from non-matching IP addresses will be
rejected, however this will cause problems when requests are routed
via a cluster of DNS servers.
Don't try to configure IP address or MTU.
This should only be used if you have already configured the device that will be
Increase debug level. Level 1 prints info about each RX/TX packet.
On level 2 (-DD) or higher, DNS queries will be printed literally.
When using Base128 upstream encoding, this is best viewed as
ISO Latin-1 text instead of (illegal) UTF-8.
This is easily done with : "LC_ALL=C luit iodined -DD ..."
Set 'mtu' as mtu size for the tun device.
This will be sent to the client on login, and the client will use the same mtu
for its tun device. Default 1130. Note that the DNS traffic will be
automatically fragmented when needed.
Make the server listen only on 'listen_ip' for incoming requests.
By default, incoming requests are accepted from all interfaces.
Make the server listen on 'port' instead of 53 for traffic.
You must make sure the dns requests are forwarded to this port yourself.
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 forwarding is not fully transparent, and not advised for use
in production environments.
The nameserver to use to relay the dns traffic. This can be any relaying
nameserver or the server running iodined if reachable. This field can be
given as an IP address, or as a hostname. This argument is optional, and
if not specified a nameserver will be read from the
The dns traffic will be sent as queries for subdomains under
'topdomain'. This is normally a subdomain to a domain you own. Use a short
domain name to get better throughput. If
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 server's ip address on the tun 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
The dns traffic is expected to arrive as queries 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. Queries for domains other
than 'topdomain' will be forwarded when the -b option is given, otherwise
they will be dropped.
See the README file for both a quick test scenario, and a detailed description
of real-world deployment.
Login is a relatively secure challenge-response MD5 hash, with the
password never passing the wire.
However, all other data is
encrypted in any way. The DNS traffic is also vulnerable to replay,
injection and man-in-the-middle attacks, especially when iodined is used
with the -c option. Use of ssh or vpn tunneling is strongly recommended.
On both server and client, use
or other firewalls to block all traffic coming in from the tun interfaces,
except to the used ssh or vpn ports.
If the environment variable
is set, iodine will use the value it is set to as password instead of asking
for one. The
option still has precedence.
If the environment variable
is set, iodined will use the value it is set to as password instead of asking
for one. The
option still has precedence.
The README file in the source distribution contains some more elaborate