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286 lines
13 KiB
Plaintext
286 lines
13 KiB
Plaintext
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iodine - http://code.kryo.se/iodine
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***********************************
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This is a piece of software that lets you tunnel IPv4 data through a DNS
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server. This can be usable in different situations where internet access is
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firewalled, but DNS queries are allowed.
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QUICKSTART:
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Try it out within your own LAN! Follow these simple steps:
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- On your server, run: ./iodined -f 10.0.0.1 test.asdf
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(If you already use the 10.0.0.0 network, use another internal net like
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172.16.0.0)
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- Enter a password
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- On the client, run: ./iodine -f 192.168.0.1 test.asdf
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(Replace 192.168.0.1 with the server's ip address)
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- Enter the same password
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- Now the client has the tunnel ip 10.0.0.2 and the server has 10.0.0.1
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- Try pinging each other through the tunnel
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- Done! :)
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To actually use it through a relaying nameserver, see below.
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HOW TO USE:
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Server side:
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To use this tunnel, you need control over a real domain (like mytunnel.com),
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and a server with a public IP number. If the server already runs a DNS
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server, change the listening port and then use the -b option to let
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iodined forward the DNS requests. Then, delegate a subdomain
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(say, tunnel1.mytunnel.com) to the server. If you use BIND for the domain,
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add these lines to the zone file:
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tunnel1host IN A 10.15.213.99
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tunnel1 IN NS tunnel1host.mytunnel.com.
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Do not use CNAME instead of A above.
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If your server has a dynamic IP, use a dynamic dns provider:
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tunnel1 IN NS tunnel1host.mydyndnsprovider.com
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Now any DNS querys for domains ending with tunnel1.mytunnnel.com will be sent
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to your server. Start iodined on the server. The first argument is the tunnel
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IP address (like 192.168.99.1) and the second is the assigned domain (in this
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case tunnel1.mytunnel.com). The -f argument will keep iodined running in the
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foreground, which helps when testing. iodined will start a virtual interface,
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and also start listening for DNS queries on UDP port 53. Either enter a
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password on the commandline (-P pass) or after the server has started. Now
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everything is ready for the client.
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Client side:
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All the setup is done, just start iodine. It takes up to two arguments, the
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first is the local relaying DNS server (optional) and the second is the domain
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used (tunnel1.mytunnnel.com). If DNS queries are allowed to any computer, you
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can use the tunnel endpoint (example: 10.15.213.99 or tunnel1host.mytunnel.com)
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as the first argument. The tunnel interface will get an IP close to the servers
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(in this case 192.168.99.2) and a suitable MTU. Enter the same password as on
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the server either by argument or after the client has started. Now you should
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be able to ping the other end of the tunnel from either side.
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MISC. INFO:
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Routing:
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The normal case is to route all traffic through the DNS tunnel. To do this, first
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add a route to the nameserver you use with the default gateway as gateway. Then
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replace the default gateway with the servers IP address within the DNS tunnel,
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and configure the server to do NAT.
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The DNS-response fragment size is normally autoprobed to get maximum bandwidth.
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To force a specific value (and speed things up), use the -m option.
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The iodined server replies to NS requests sent for subdomains of the tunnel
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domain. If your domain is tunnel.com, send a NS request for foo.tunnel.com
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to see if the delegation works. dig is a good tool for this:
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dig -t NS foo123.tunnel.com
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The upstream data is sent gzipped encoded with Base32, or Base64 if the relay
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server support '+' in domain names. DNS protocol allows one query per packet,
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and one query can be max 256 chars. Each domain name part can be max 63 chars.
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So your domain name and subdomain should be as short as possible to allow
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maximum upstream throughput.
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The default is to use DNS NULL-type queries, as this provides the largest
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downstream bandwidth. If your DNS server blocks NULL requests, try TXT or
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CNAME queries via the -T option. Also supported are A (returning CNAME) and
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MX requests, but these may/will cause additional lookups by "smart" caching
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nameservers to get an actual IP address, which may either slow down or fail
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completely. DNS responses for non-NULL are Base32 encoded by default, which
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should always work. For more bandwidth, try Base64 or Raw (TXT only) via the
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-O option. If Base64/Raw doesn't work, you'll see many failures in the
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fragment size autoprobe.
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Normal operation now is for the server to _not_ answer a DNS request until
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the next DNS request has come in, a.k.a. being "lazy". This way, the server
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will always have a DNS request handy when new downstream data has to be sent.
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This greatly improves (interactive) performance and latency, and allows to
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slow down the quiescent ping requests to 4 second intervals by default.
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In fact, the main purpose of the pings now is to force a reply to the previous
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ping, and prevent DNS server timeouts (usually 5-10 seconds per RFC1035).
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In the unlikely case that you do experience DNS server timeouts (SERVFAIL),
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decrease the -I option to 1. If you are running on a local network without
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any DNS server in-between, try -I 50 (iodine and iodined time out after 60
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seconds). The only time you'll notice a slowdown, is when DNS reply packets
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go missing; the iodined server then has to wait for a new ping to re-send the
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data. You can speed this up by generating some upstream traffic (keypress,
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ping). If this happens often, check your network for bottlenecks and/or run
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with -I1 .
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Some DNS servers appear to be quite impatient and start retrying DNS requests
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(with _different_ DNS ids!) when an answer does not appear within a few
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milliseconds. Usually they scale back retries when iodined's lazy mode
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repeatedly takes several seconds to answer; and they scale up retries again
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when iodined answers fast during heavy data transfer. Some commercial DNS
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servers advertise this as "carrier-grade adaptive retransmission techniques".
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The effect will only be visible in the network traffic at the iodined server,
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and will not affect the client's connection. Iodined has rather elaborate
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logic to deal with (i.e., ignore) these unwanted duplicates.
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Other DNS servers, notably the opendns.com network, seem to regard iodined's
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lazyness as incompetency, and will start shuffling requests around, possibly
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in an attempt to reduce iodined's workload. The resulting out-of-sequence DNS
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traffic works quite badly for lazy mode. The iodine client will detect this,
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and switch back to legacy mode ("immediate ping-pong") automatically. In these
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cases, start the iodine client with -L0 to prevent it from operating in lazy
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mode altogether. Note that this will negatively affect interactive performance
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and latency, especially in the downstream direction.
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If you have problems, try inspecting the traffic with network monitoring tools
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and make sure that the relaying DNS server has not cached the response. A
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cached error message could mean that you started the client before the server.
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The -D (and -DD) option on the server can also show received and sent queries.
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TIPS & TRICKS:
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If your port 53 is taken on a specific interface by an application that does
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not use it, use -p on iodined to specify an alternate port (like -p 5353) and
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use for instance iptables (on Linux) to forward the traffic:
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iptables -t nat -A PREROUTING -i eth0 -p udp --dport 53 -j DNAT --to :5353
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(Sent in by Tom Schouten)
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Iodined will reject data from clients that have not been active (data/pings)
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for more than 60 seconds. Similarly, iodine will exit when no downstream
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data has been received for 60 seconds. In case of a long network outage or
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similar, just restart iodine (re-login), possibly multiple times until you get
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your old IP address back. Once that's done, just wait a while, and you'll
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eventually see the tunneled TCP traffic continue to flow from where it left
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off before the outage.
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With the introduction of the downstream packet queue in the server, its memory
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usage has increased with several megabytes in the default configuration.
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For use in low-memory environments (e.g. running on your DSL router), you can
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decrease USERS and undefine OUTPACKETQ_LEN in user.h without any ill conse-
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quence, assuming at most one client will be connected at any time. A small
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DNSCACHE_LEN is still advised, preferably 2 or higher, however you can also
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undefine it to save a few more kilobytes.
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PERFORMANCE:
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This section tabulates some performance measurements. To view properly, use
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a fixed-width font like Courier.
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Measurements were done in protocol 00000500 with lazy mode unless indicated
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otherwise. Upstream encoding always Base64.
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Upstream/downstream throughput was measured by scp'ing a file previously
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read from /dev/urandom (i.e. incompressible), and measuring size with
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"ls -l ; sleep 30 ; ls -l" on a separate non-tunneled connection. Given the
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large scp block size of 16 kB, this gives a resolution of 4.3 kbit/s, which
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explains why many values are exactly equal.
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Ping round-trip times measured with "ping -c100", presented are average rtt
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and mean deviation (indicating spread around the average), in milliseconds.
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Situation 1:
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Laptop -> Wifi AP -> Home server -> DSL provider -> Datacenter
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iodine DNS "relay" bind9 DNS cache iodined
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downstr. upstream downstr. ping-up ping-down
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fragsize kbit/s kbit/s avg +/-mdev avg +/-mdev
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------------------------------------------------------------------------------
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iodine -> Wifi AP :53
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-Tnull (= -Oraw) 982 39.3 148.5 26.7 3.1 26.6 3.0
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iodine -> Home server :53
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-Tnull (= -Oraw) 1174 43.6 174.7 25.2 4.0 25.5 3.4
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iodine -> DSL provider :53
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-Tnull (= -Oraw) 1174 52.4 200.9 20.3 3.2 20.3 2.7
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-Ttxt -Obase32 730 52.4 192.2*
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-Ttxt -Obase64 874 52.4 192.2
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-Ttxt -Oraw 1162 52.4 192.2
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-Tcname -Obase32 148 52.4 48.0
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-Tcname -Obase64 181 52.4 61.1
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iodine -> DSL provider :53
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wired (no Wifi) -Tnull 1174 65.5 244.6 17.7 1.9 17.8 1.6
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[192.2* : nice, because still 2frag/packet]
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Situation 2:
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Laptop -> (wire) -> (Home server) -> (DSL) -> opendns.com -> Datacenter
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iodine DNS cache iodined
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downstr. upstream downstr. ping-up ping-down
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fragsize kbit/s kbit/s avg +/-mdev avg +/-mdev
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------------------------------------------------------------------------------
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iodine -> opendns.com :53
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-Tnull -L1 (lazy mode) 230 - - 404.4 196.2 663.8 679.6
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(20% lost) (2% lost)
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-Tnull -L0 (legacy mode) 230 5.6 7.4 197.3 4.7 610.8 323.5
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[Note: Throughput measured over 300 seconds to get better resolution]
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Situation 3:
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Laptop -> Wifi+vpn / wired -> Home server
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iodine iodined
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downstr. upstream downstr. ping-up ping-down
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fragsize kbit/s kbit/s avg +/-mdev avg +/-mdev
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------------------------------------------------------------------------------
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wifi + openvpn -Tnull 1186 183.5 611.6 5.7 1.4 7.0 2.7
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wired -Tnull 1186 685.9 2350.5 1.3 0.1 1.4 0.4
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Performance is strongly coupled to low ping times, as iodine requires
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confirmation for every data fragment before moving on to the next. Allowing
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multiple fragments in-flight like TCP could possibly increase performance,
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but it would likely cause serious overload for the intermediary DNS servers.
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The current protocol scales performance with DNS responsivity, since the
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DNS servers are on average handling at most one DNS request per client.
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PORTABILITY:
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iodine has been tested on Linux (arm, ia64, x86, AMD64 and SPARC64), FreeBSD
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(ia64, x86), OpenBSD (x86), NetBSD (x86), MacOS X (ppc and x86, with
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http://tuntaposx.sourceforge.net/). and Windows (with OpenVPN TAP32 driver, see
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win32 readme file). It should be easy to port to other unix-like systems that
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has TUN/TAP tunneling support. Let us know if you get it to run on other
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platforms.
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THE NAME:
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The name iodine was chosen since it starts with IOD (IP Over DNS) and since
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iodine has atomic number 53, which happens to be the DNS port number.
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THANKS:
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- To kuxien for FreeBSD and OS X testing
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- To poplix for code audit
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AUTHORS & LICENSE:
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Copyright (c) 2006-2009 Bjorn Andersson <flex@kryo.se>, Erik Ekman <yarrick@kryo.se>
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Permission to use, copy, modify, and distribute this software for any purpose
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with or without fee is hereby granted, provided that the above copyright notice
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and this permission notice appear in all copies.
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THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES WITH
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REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY AND
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FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT,
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INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM
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LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR
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OTHER TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR
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PERFORMANCE OF THIS SOFTWARE.
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MD5 implementation by L. Peter Deutsch (license and source in src/md5.[ch])
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Copyright (C) 1999, 2000, 2002 Aladdin Enterprises. All rights reserved.
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