start merging common and docs #76

This commit is contained in:
J. A. Bezemer 2009-09-20 21:10:38 +00:00 committed by Erik Ekman
parent 92b160a416
commit 05e99c7a3f
4 changed files with 185 additions and 2 deletions

130
README
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@ -94,6 +94,41 @@ 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.
@ -109,12 +144,103 @@ 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. In case of a long network outage or similar, just
stop iodine and restart (re-login), possibly multiple times until you get
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:

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@ -83,6 +83,12 @@ Server sends:
Server may disregard this option; client must always use the downstream
encoding type indicated in every downstream DNS packet.
l or L: Lazy mode, server will keep one request unanswered until the
next one comes in. Applies only to data transfer; handshake is always
answered immediately.
i or I: Immediate (non-lazy) mode, server will answer all requests
(nearly) immediately.
Probe downstream fragment size:
Client sends:
First byte r or R
@ -162,6 +168,39 @@ If server has something to send, it will send a downstream data packet,
prefixed with 2 bytes header as shown above.
"Lazy-mode" operation
=====================
Client-server DNS traffic sequence has been reordered to provide increased
(interactive) performance and greatly reduced latency.
Idea taken from Lucas Nussbaum's slides (24th IFIP International Security
Conference, 2009) at http://www.loria.fr/~lnussbau/tuns.html. Current
implementation is original to iodine, no code or documentation from any other
project was consulted during development.
Server:
Upstream data is acked immediately*, to keep the slow upstream data flowing
as fast as possible (client waits for ack to send next frag).
Upstream pings are answered _only_ when 1) downstream data arrives from tun,
OR 2) new upstream ping/data arrives from client.
In most cases, this means we answer the previous DNS query instead of the
current one. The current query is kept in queue and used as soon as
downstream data has to be sent.
*: upstream data ack is usually done as reply on the previous ping packet,
and the upstream-data packet itself is kept in queue.
Client:
Downstream data is acked immediately, to keep it flowing fast (includes a
ping after last downstream frag).
Also, after all available upstream data is sent & acked by the server (which
in some cases uses up the last query), send an additional ping to prime the
server for the next downstream data.
======================================================
2. Raw UDP protocol
======================================================

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@ -333,3 +333,18 @@ errx(int eval, const char *fmt, ...)
}
#endif
int recent_seqno(int ourseqno, int gotseqno)
/* Return 1 if we've seen gotseqno recently (current or up to 3 back).
Return 0 if gotseqno is new (or very old).
*/
{
int i;
for (i = 0; i < 4; i++, ourseqno--) {
if (ourseqno < 0)
ourseqno = 7;
if (gotseqno == ourseqno)
return 1;
}
return 0;
}

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@ -88,6 +88,7 @@ struct query {
char name[QUERY_NAME_SIZE];
unsigned short type;
unsigned short id;
unsigned short iddupe; /* only used for dupe checking */
struct in_addr destination;
struct sockaddr from;
int fromlen;
@ -121,4 +122,6 @@ void errx(int eval, const char *fmt, ...);
void warnx(const char *fmt, ...);
#endif
int recent_seqno(int , int);
#endif