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 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: tunnel1host IN A 10.15.213.99 tunnel1 IN NS tunnel1host.mytunnel.com. Do not use CNAME instead of A above. If your server has a dynamic IP, use a dynamic dns provider: tunnel1 IN NS tunnel1host.mydyndnsprovider.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. Client side: All the setup is done, just start iodine. It takes up to two arguments, the first is the local relaying DNS server (optional) 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: Routing: 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. The DNS-response fragment size is normally autoprobed to get maximum bandwidth. To force a specific value (and speed things up), use the -m option. The iodined server replies to NS requests sent for subdomains of the tunnel domain. If your domain is tunnel.com, send a NS request for foo.tunnel.com to see if the delegation works. dig is a good tool for this: dig -t NS foo123.tunnel.com The upstream data is sent gzipped encoded with Base32, or Base64 if the relay server support '+' in domain names. 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 upstream throughput. The default is to use DNS NULL-type queries, as this provides the largest downstream bandwidth. If your DNS server blocks NULL requests, try TXT or CNAME queries via the -T option. Also supported are A (returning CNAME) and MX requests, but these may/will cause additional lookups by "smart" caching nameservers to get an actual IP address, which may either slow down or fail completely. DNS responses for non-NULL are Base32 encoded by default, which should always work. For more bandwidth, try Base64 or Raw (TXT only) via the -O option. If Base64/Raw doesn't work, you'll see many failures in the fragment size autoprobe. Normal operation now is for the server to _not_ answer a DNS request until the next DNS request has come in, a.k.a. being "lazy". This way, the server will always have a DNS request handy when new downstream data has to be sent. This greatly improves (interactive) performance and latency, and allows to slow down the quiescent ping requests to 4 second intervals by default. In fact, the main purpose of the pings now is to force a reply to the previous ping, and prevent DNS server timeouts (usually 5-10 seconds per RFC1035). In the unlikely case that you do experience DNS server timeouts (SERVFAIL), decrease the -I option to 1. If you are running on a local network without any DNS server in-between, try -I 50 (iodine and iodined time out after 60 seconds). The only time you'll notice a slowdown, is when DNS reply packets go missing; the iodined server then has to wait for a new ping to re-send the data. You can speed this up by generating some upstream traffic (keypress, ping). If this happens often, check your network for bottlenecks and/or run with -I1 . Some DNS servers appear to be quite impatient and start retrying DNS requests (with _different_ DNS ids!) when an answer does not appear within a few milliseconds. Usually they scale back retries when iodined's lazy mode repeatedly takes several seconds to answer; and they scale up retries again when iodined answers fast during heavy data transfer. Some commercial DNS servers advertise this as "carrier-grade adaptive retransmission techniques". The effect will only be visible in the network traffic at the iodined server, and will not affect the client's connection. Iodined has rather elaborate logic to deal with (i.e., ignore) these unwanted duplicates. Other DNS servers, notably the opendns.com network, seem to regard iodined's lazyness as incompetency, and will start shuffling requests around, possibly in an attempt to reduce iodined's workload. The resulting out-of-sequence DNS traffic works quite badly for lazy mode. The iodine client will detect this, and switch back to legacy mode ("immediate ping-pong") automatically. In these cases, start the iodine client with -L0 to prevent it from operating in lazy mode altogether. Note that this will negatively affect interactive performance and latency, especially in the downstream direction. 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 -D (and -DD) option on the server can also show received and sent queries. 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) Iodined will reject data from clients that have not been active (data/pings) for more than 60 seconds. Similarly, iodine will exit when no downstream data has been received for 60 seconds. In case of a long network outage or similar, just restart iodine (re-login), possibly multiple times until you get your old IP address back. Once that's done, just wait a while, and you'll eventually see the tunneled TCP traffic continue to flow from where it left off before the outage. With the introduction of the downstream packet queue in the server, its memory usage has increased with several megabytes in the default configuration. For use in low-memory environments (e.g. running on your DSL router), you can decrease USERS and undefine OUTPACKETQ_LEN in user.h without any ill conse- quence, assuming at most one client will be connected at any time. A small DNSCACHE_LEN is still advised, preferably 2 or higher, however you can also undefine it to save a few more kilobytes. PERFORMANCE: This section tabulates some performance measurements. To view properly, use a fixed-width font like Courier. Measurements were done in protocol 00000500 with lazy mode unless indicated otherwise. Upstream encoding always Base64. Upstream/downstream throughput was measured by scp'ing a file previously read from /dev/urandom (i.e. incompressible), and measuring size with "ls -l ; sleep 30 ; ls -l" on a separate non-tunneled connection. Given the large scp block size of 16 kB, this gives a resolution of 4.3 kbit/s, which explains why many values are exactly equal. Ping round-trip times measured with "ping -c100", presented are average rtt and mean deviation (indicating spread around the average), in milliseconds. Situation 1: Laptop -> Wifi AP -> Home server -> DSL provider -> Datacenter iodine DNS "relay" bind9 DNS cache iodined downstr. upstream downstr. ping-up ping-down fragsize kbit/s kbit/s avg +/-mdev avg +/-mdev ------------------------------------------------------------------------------ iodine -> Wifi AP :53 -Tnull (= -Oraw) 982 39.3 148.5 26.7 3.1 26.6 3.0 iodine -> Home server :53 -Tnull (= -Oraw) 1174 43.6 174.7 25.2 4.0 25.5 3.4 iodine -> DSL provider :53 -Tnull (= -Oraw) 1174 52.4 200.9 20.3 3.2 20.3 2.7 -Ttxt -Obase32 730 52.4 192.2* -Ttxt -Obase64 874 52.4 192.2 -Ttxt -Oraw 1162 52.4 192.2 -Tcname -Obase32 148 52.4 48.0 -Tcname -Obase64 181 52.4 61.1 iodine -> DSL provider :53 wired (no Wifi) -Tnull 1174 65.5 244.6 17.7 1.9 17.8 1.6 [192.2* : nice, because still 2frag/packet] Situation 2: Laptop -> (wire) -> (Home server) -> (DSL) -> opendns.com -> Datacenter iodine DNS cache iodined downstr. upstream downstr. ping-up ping-down fragsize kbit/s kbit/s avg +/-mdev avg +/-mdev ------------------------------------------------------------------------------ iodine -> opendns.com :53 -Tnull -L1 (lazy mode) 230 - - 404.4 196.2 663.8 679.6 (20% lost) (2% lost) -Tnull -L0 (legacy mode) 230 5.6 7.4 197.3 4.7 610.8 323.5 [Note: Throughput measured over 300 seconds to get better resolution] Situation 3: Laptop -> Wifi+vpn / wired -> Home server iodine iodined downstr. upstream downstr. ping-up ping-down fragsize kbit/s kbit/s avg +/-mdev avg +/-mdev ------------------------------------------------------------------------------ wifi + openvpn -Tnull 1186 183.5 611.6 5.7 1.4 7.0 2.7 wired -Tnull 1186 685.9 2350.5 1.3 0.1 1.4 0.4 Performance is strongly coupled to low ping times, as iodine requires confirmation for every data fragment before moving on to the next. Allowing multiple fragments in-flight like TCP could possibly increase performance, but it would likely cause serious overload for the intermediary DNS servers. The current protocol scales performance with DNS responsivity, since the DNS servers are on average handling at most one DNS request per client. PORTABILITY: iodine has been tested on Linux (arm, ia64, x86, AMD64 and SPARC64), FreeBSD (ia64, x86), OpenBSD (x86), NetBSD (x86), MacOS X (ppc and x86, with http://tuntaposx.sourceforge.net/). and Windows (with OpenVPN TAP32 driver, see win32 readme file). It should be easy to port to other unix-like systems that has TUN/TAP tunneling support. 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) 2006-2009 Bjorn Andersson , Erik Ekman 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.