1 \input texinfo @c -*-texinfo-*-
9 @include tincinclude.texi
12 @dircategory Networking tools
14 * tinc: (tinc). The tinc Manual.
17 This is the info manual for @value{PACKAGE} version @value{VERSION}, a Virtual Private Network daemon.
19 Copyright @copyright{} 1998-2005 Ivo Timmermans
20 <ivo@@tinc-vpn.org>, Guus Sliepen <guus@@tinc-vpn.org> and
21 Wessel Dankers <wsl@@tinc-vpn.org>.
25 Permission is granted to make and distribute verbatim copies of this
26 manual provided the copyright notice and this permission notice are
27 preserved on all copies.
29 Permission is granted to copy and distribute modified versions of this
30 manual under the conditions for verbatim copying, provided that the
31 entire resulting derived work is distributed under the terms of a
32 permission notice identical to this one.
38 @subtitle Setting up a Virtual Private Network with tinc
39 @author Ivo Timmermans and Guus Sliepen
42 @vskip 0pt plus 1filll
44 This is the info manual for @value{PACKAGE} version @value{VERSION}, a Virtual Private Network daemon.
46 Copyright @copyright{} 1998-2005 Ivo Timmermans
47 <ivo@@tinc-vpn.org>, Guus Sliepen <guus@@tinc-vpn.org> and
48 Wessel Dankers <wsl@@tinc-vpn.org>.
52 Permission is granted to make and distribute verbatim copies of this
53 manual provided the copyright notice and this permission notice are
54 preserved on all copies.
56 Permission is granted to copy and distribute modified versions of this
57 manual under the conditions for verbatim copying, provided that the
58 entire resulting derived work is distributed under the terms of a
59 permission notice identical to this one.
64 @c ==================================================================
74 * Technical information::
75 * Platform specific information::
77 * Concept Index:: All used terms explained
81 @c ==================================================================
86 Tinc is a Virtual Private Network (VPN) daemon that uses tunneling and
87 encryption to create a secure private network between hosts on the
90 Because the tunnel appears to the IP level network code as a normal
91 network device, there is no need to adapt any existing software.
92 The encrypted tunnels allows VPN sites to share information with each other
93 over the Internet without exposing any information to others.
95 This document is the manual for tinc. Included are chapters on how to
96 configure your computer to use tinc, as well as the configuration
97 process of tinc itself.
100 * Virtual Private Networks::
102 * Supported platforms::
105 @c ==================================================================
106 @node Virtual Private Networks
107 @section Virtual Private Networks
110 A Virtual Private Network or VPN is a network that can only be accessed
111 by a few elected computers that participate. This goal is achievable in
112 more than just one way.
115 Private networks can consist of a single stand-alone Ethernet LAN. Or
116 even two computers hooked up using a null-modem cable. In these cases,
118 obvious that the network is @emph{private}, no one can access it from the
119 outside. But if your computers are linked to the Internet, the network
120 is not private anymore, unless one uses firewalls to block all private
121 traffic. But then, there is no way to send private data to trusted
122 computers on the other end of the Internet.
125 This problem can be solved by using @emph{virtual} networks. Virtual
126 networks can live on top of other networks, but they use encapsulation to
127 keep using their private address space so they do not interfere with
128 the Internet. Mostly, virtual networks appear like a singe LAN, even though
129 they can span the entire world. But virtual networks can't be secured
130 by using firewalls, because the traffic that flows through it has to go
131 through the Internet, where other people can look at it.
133 As is the case with either type of VPN, anybody could eavesdrop. Or
134 worse, alter data. Hence it's probably advisable to encrypt the data
135 that flows over the network.
137 When one introduces encryption, we can form a true VPN. Other people may
138 see encrypted traffic, but if they don't know how to decipher it (they
139 need to know the key for that), they cannot read the information that flows
140 through the VPN. This is what tinc was made for.
143 @c ==================================================================
148 I really don't quite remember what got us started, but it must have been
149 Guus' idea. He wrote a simple implementation (about 50 lines of C) that
150 used the ethertap device that Linux knows of since somewhere
151 about kernel 2.1.60. It didn't work immediately and he improved it a
152 bit. At this stage, the project was still simply called "vpnd".
154 Since then, a lot has changed---to say the least.
157 Tinc now supports encryption, it consists of a single daemon (tincd) for
158 both the receiving and sending end, it has become largely
159 runtime-configurable---in short, it has become a full-fledged
160 professional package.
162 @cindex traditional VPNs
164 Tinc also allows more than two sites to connect to eachother and form a single VPN.
165 Traditionally VPNs are created by making tunnels, which only have two endpoints.
166 Larger VPNs with more sites are created by adding more tunnels.
167 Tinc takes another approach: only endpoints are specified,
168 the software itself will take care of creating the tunnels.
169 This allows for easier configuration and improved scalability.
171 A lot can---and will be---changed. We have a number of things that we would like to
172 see in the future releases of tinc. Not everything will be available in
173 the near future. Our first objective is to make tinc work perfectly as
174 it stands, and then add more advanced features.
176 Meanwhile, we're always open-minded towards new ideas. And we're
180 @c ==================================================================
181 @node Supported platforms
182 @section Supported platforms
185 Tinc has been verified to work under Linux, FreeBSD, OpenBSD, NetBSD, MacOS/X (Darwin), Solaris, and Windows (both natively and in a Cygwin environment),
186 with various hardware architectures. These are some of the platforms
187 that are supported by the universal tun/tap device driver or other virtual network device drivers.
188 Without such a driver, tinc will most
189 likely compile and run, but it will not be able to send or receive data
193 For an up to date list of supported platforms, please check the list on
195 @uref{http://www.tinc-vpn.org/platforms}.
203 @c Preparing your system
210 @c ==================================================================
212 @chapter Preparations
214 This chapter contains information on how to prepare your system to
218 * Configuring the kernel::
223 @c ==================================================================
224 @node Configuring the kernel
225 @section Configuring the kernel
228 * Configuration of Linux kernels 2.1.60 up to 2.4.0::
229 * Configuration of Linux kernels 2.4.0 and higher::
230 * Configuration of FreeBSD kernels::
231 * Configuration of OpenBSD kernels::
232 * Configuration of NetBSD kernels::
233 * Configuration of Solaris kernels::
234 * Configuration of Darwin (MacOS/X) kernels::
235 * Configuration of Windows::
239 @c ==================================================================
240 @node Configuration of Linux kernels 2.1.60 up to 2.4.0
241 @subsection Configuration of Linux kernels 2.1.60 up to 2.4.0
244 For kernels up to 2.4.0, you need a kernel that supports the ethertap device.
245 Most distributions come with kernels that already support this.
246 If not, here are the options you have to turn on when configuring a new kernel:
249 Code maturity level options
250 [*] Prompt for development and/or incomplete code/drivers
252 [*] Kernel/User netlink socket
253 <M> Netlink device emulation
254 Network device support
255 <M> Ethertap network tap
258 If you want to run more than one instance of tinc or other programs that use
259 the ethertap, you have to compile the ethertap driver as a module, otherwise
260 you can also choose to compile it directly into the kernel.
262 If you decide to build any of these as dynamic kernel modules, it's a good idea
263 to add these lines to @file{/etc/modules.conf}:
266 alias char-major-36 netlink_dev
268 options tap0 -o tap0 unit=0
270 options tap1 -o tap1 unit=1
272 alias tap@emph{N} ethertap
273 options tap@emph{N} -o tap@emph{N} unit=@emph{N}
276 Add as much alias/options lines as necessary.
279 @c ==================================================================
280 @node Configuration of Linux kernels 2.4.0 and higher
281 @subsection Configuration of Linux kernels 2.4.0 and higher
283 @cindex Universal tun/tap
284 For kernels 2.4.0 and higher, you need a kernel that supports the Universal tun/tap device.
285 Most distributions come with kernels that already support this.
286 Here are the options you have to turn on when configuring a new kernel:
289 Code maturity level options
290 [*] Prompt for development and/or incomplete code/drivers
291 Network device support
292 <M> Universal tun/tap device driver support
295 It's not necessary to compile this driver as a module, even if you are going to
296 run more than one instance of tinc.
298 If you have an early 2.4 kernel, you can choose both the tun/tap driver and the
299 `Ethertap network tap' device. This latter is marked obsolete, and chances are
300 that it won't even function correctly anymore. Make sure you select the
301 universal tun/tap driver.
303 If you decide to build the tun/tap driver as a kernel module, add these lines
304 to @file{/etc/modules.conf}:
307 alias char-major-10-200 tun
311 @c ==================================================================
312 @node Configuration of FreeBSD kernels
313 @subsection Configuration of FreeBSD kernels
315 For FreeBSD version 4.1 and higher, tun and tap drivers are included in the default kernel configuration.
316 Using tap devices is recommended.
319 @c ==================================================================
320 @node Configuration of OpenBSD kernels
321 @subsection Configuration of OpenBSD kernels
323 For OpenBSD version 2.9 and higher,
324 the tun driver is included in the default kernel configuration.
325 There is also a kernel patch from @uref{http://diehard.n-r-g.com/stuff/openbsd/}
326 which adds a tap device to OpenBSD.
327 This should work with tinc.
330 @c ==================================================================
331 @node Configuration of NetBSD kernels
332 @subsection Configuration of NetBSD kernels
334 For NetBSD version 1.5.2 and higher,
335 the tun driver is included in the default kernel configuration.
337 Tunneling IPv6 may not work on NetBSD's tun device.
340 @c ==================================================================
341 @node Configuration of Solaris kernels
342 @subsection Configuration of Solaris kernels
344 For Solaris 8 (SunOS 5.8) and higher,
345 the tun driver may or may not be included in the default kernel configuration.
346 If it isn't, the source can be downloaded from @uref{http://vtun.sourceforge.net/tun/}.
347 For x86 and sparc64 architectures, precompiled versions can be found at @uref{http://www.monkey.org/~dugsong/fragroute/}.
348 If the @file{net/if_tun.h} header file is missing, install it from the source package.
351 @c ==================================================================
352 @node Configuration of Darwin (MacOS/X) kernels
353 @subsection Configuration of Darwin (MacOS/X) kernels
355 Tinc on Darwin relies on a tunnel driver for its data acquisition from the kernel.
356 Tinc supports either the driver from @uref{http://www-user.rhrk.uni-kl.de/~nissler/tuntap/},
357 which supports both tun and tap style devices,
358 and also the driver from from @uref{http://chrisp.de/en/projects/tunnel.html}.
359 The former driver is recommended.
360 The tunnel driver must be loaded before starting tinc with the following command:
367 @c ==================================================================
368 @node Configuration of Windows
369 @subsection Configuration of Windows
371 You will need to install the latest TAP-Win32 driver from OpenVPN.
372 You can download it from @uref{http://openvpn.sourceforge.net}.
373 Using the Network Connections control panel,
374 configure the TAP-Win32 network interface in the same way as you would do from the tinc-up script,
375 as explained in the rest of the documentation.
378 @c ==================================================================
384 Before you can configure or build tinc, you need to have the OpenSSL,
385 zlib and lzo libraries installed on your system. If you try to configure tinc without
386 having them installed, configure will give you an error message, and stop.
395 @c ==================================================================
400 For all cryptography-related functions, tinc uses the functions provided
401 by the OpenSSL library.
403 If this library is not installed, you wil get an error when configuring
404 tinc for build. Support for running tinc without having OpenSSL
405 installed @emph{may} be added in the future.
407 You can use your operating system's package manager to install this if
408 available. Make sure you install the development AND runtime versions
411 If you have to install OpenSSL manually, you can get the source code
412 from @url{http://www.openssl.org/}. Instructions on how to configure,
413 build and install this package are included within the package. Please
414 make sure you build development and runtime libraries (which is the
417 If you installed the OpenSSL libraries from source, it may be necessary
418 to let configure know where they are, by passing configure one of the
419 --with-openssl-* parameters.
422 --with-openssl=DIR OpenSSL library and headers prefix
423 --with-openssl-include=DIR OpenSSL headers directory
424 (Default is OPENSSL_DIR/include)
425 --with-openssl-lib=DIR OpenSSL library directory
426 (Default is OPENSSL_DIR/lib)
430 @subsubheading License
433 The complete source code of tinc is covered by the GNU GPL version 2.
434 Since the license under which OpenSSL is distributed is not directly
435 compatible with the terms of the GNU GPL
436 @uref{http://www.openssl.org/support/faq.html#LEGAL2}, we
437 include an exemption to the GPL (see also the file COPYING.README) to allow
438 everyone to create a statically or dynamically linked executable:
441 This program is released under the GPL with the additional exemption
442 that compiling, linking, and/or using OpenSSL is allowed. You may
443 provide binary packages linked to the OpenSSL libraries, provided that
444 all other requirements of the GPL are met.
447 Since the LZO library used by tinc is also covered by the GPL,
448 we also present the following exemption:
451 Hereby I grant a special exception to the tinc VPN project
452 (http://www.tinc-vpn.org/) to link the LZO library with the OpenSSL library
453 (http://www.openssl.org).
455 Markus F.X.J. Oberhumer
459 @c ==================================================================
464 For the optional compression of UDP packets, tinc uses the functions provided
467 If this library is not installed, you wil get an error when configuring
468 tinc for build. Support for running tinc without having zlib
469 installed @emph{may} be added in the future.
471 You can use your operating system's package manager to install this if
472 available. Make sure you install the development AND runtime versions
475 If you have to install zlib manually, you can get the source code
476 from @url{http://www.gzip.org/zlib/}. Instructions on how to configure,
477 build and install this package are included within the package. Please
478 make sure you build development and runtime libraries (which is the
482 @c ==================================================================
487 Another form of compression is offered using the lzo library.
489 If this library is not installed, you wil get an error when configuring
490 tinc for build. Support for running tinc without having lzo
491 installed @emph{may} be added in the future.
493 You can use your operating system's package manager to install this if
494 available. Make sure you install the development AND runtime versions
497 If you have to install lzo manually, you can get the source code
498 from @url{http://www.oberhumer.com/opensource/lzo/}. Instructions on how to configure,
499 build and install this package are included within the package. Please
500 make sure you build development and runtime libraries (which is the
513 @c ==================================================================
515 @chapter Installation
517 If you use Debian, you may want to install one of the
518 precompiled packages for your system. These packages are equipped with
519 system startup scripts and sample configurations.
521 If you cannot use one of the precompiled packages, or you want to compile tinc
522 for yourself, you can use the source. The source is distributed under
523 the GNU General Public License (GPL). Download the source from the
524 @uref{http://www.tinc-vpn.org/download, download page}, which has
525 the checksums of these files listed; you may wish to check these with
526 md5sum before continuing.
528 Tinc comes in a convenient autoconf/automake package, which you can just
529 treat the same as any other package. Which is just untar it, type
530 `./configure' and then `make'.
531 More detailed instructions are in the file @file{INSTALL}, which is
532 included in the source distribution.
535 * Building and installing tinc::
540 @c ==================================================================
541 @node Building and installing tinc
542 @section Building and installing tinc
544 Detailed instructions on configuring the source, building tinc and installing tinc
545 can be found in the file called @file{INSTALL}.
547 @cindex binary package
548 If you happen to have a binary package for tinc for your distribution,
549 you can use the package management tools of that distribution to install tinc.
550 The documentation that comes along with your distribution will tell you how to do that.
553 * Darwin (MacOS/X) build environment::
554 * Cygwin (Windows) build environment::
555 * MinGW (Windows) build environment::
559 @c ==================================================================
560 @node Darwin (MacOS/X) build environment
561 @subsection Darwin (MacOS/X) build environment
563 In order to build tinc on Darwin, you need to install the MacOS/X Developer Tools
564 from @uref{http://developer.apple.com/tools/macosxtools.html} and
565 a recent version of Fink from @uref{http://fink.sourceforge.net/}.
567 After installation use fink to download and install the following packages:
568 autoconf25, automake, dlcompat, m4, openssl, zlib and lzo.
570 @c ==================================================================
571 @node Cygwin (Windows) build environment
572 @subsection Cygwin (Windows) build environment
574 If Cygwin hasn't already been installed, install it directly from
575 @uref{http://www.cygwin.com/}.
577 When tinc is compiled in a Cygwin environment, it can only be run in this environment,
578 but all programs, including those started outside the Cygwin environment, will be able to use the VPN.
579 It will also support all features.
581 @c ==================================================================
582 @node MinGW (Windows) build environment
583 @subsection MinGW (Windows) build environment
585 You will need to install the MinGW environment from @uref{http://www.mingw.org}.
587 When tinc is compiled using MinGW it runs natively under Windows,
588 it is not necessary to keep MinGW installed.
590 When detaching, tinc will install itself as a service,
591 which will be restarted automatically after reboots.
594 @c ==================================================================
596 @section System files
598 Before you can run tinc, you must make sure you have all the needed
599 files on your system.
607 @c ==================================================================
609 @subsection Device files
612 First, you'll need the special device file(s) that form the interface
613 between the kernel and the daemon.
615 The permissions for these files have to be such that only the super user
616 may read/write to this file. You'd want this, because otherwise
617 eavesdropping would become a bit too easy. This does, however, imply
618 that you'd have to run tincd as root.
620 If you use Linux and have a kernel version prior to 2.4.0, you have to make the
624 mknod -m 600 /dev/tap0 c 36 16
625 mknod -m 600 /dev/tap1 c 36 17
627 mknod -m 600 /dev/tap@emph{N} c 36 @emph{N+16}
630 There is a maximum of 16 ethertap devices.
632 If you use the universal tun/tap driver, you have to create the
633 following device file (unless it already exist):
636 mknod -m 600 /dev/tun c 10 200
639 If you use Linux, and you run the new 2.4 kernel using the devfs filesystem,
640 then the tun/tap device will probably be automatically generated as
643 Unlike the ethertap device, you do not need multiple device files if
644 you are planning to run multiple tinc daemons.
647 @c ==================================================================
649 @subsection Other files
651 @subsubheading @file{/etc/networks}
653 You may add a line to @file{/etc/networks} so that your VPN will get a
654 symbolic name. For example:
660 @subsubheading @file{/etc/services}
663 You may add this line to @file{/etc/services}. The effect is that you
664 may supply a @samp{tinc} as a valid port number to some programs. The
665 number 655 is registered with the IANA.
670 # Ivo Timmermans <ivo@@tinc-vpn.org>
685 @c ==================================================================
687 @chapter Configuration
690 * Configuration introduction::
691 * Multiple networks::
692 * How connections work::
693 * Configuration files::
694 * Generating keypairs::
695 * Network interfaces::
696 * Example configuration::
699 @c ==================================================================
700 @node Configuration introduction
701 @section Configuration introduction
703 Before actually starting to configure tinc and editing files,
704 make sure you have read this entire section so you know what to expect.
705 Then, make it clear to yourself how you want to organize your VPN:
706 What are the nodes (computers running tinc)?
707 What IP addresses/subnets do they have?
708 What is the network mask of the entire VPN?
709 Do you need special firewall rules?
710 Do you have to set up masquerading or forwarding rules?
711 Do you want to run tinc in router mode or switch mode?
712 These questions can only be answered by yourself,
713 you will not find the answers in this documentation.
714 Make sure you have an adequate understanding of networks in general.
715 @cindex Network Administrators Guide
716 A good resource on networking is the
717 @uref{http://www.linuxdoc.org/LDP/nag2/, Linux Network Administrators Guide}.
719 If you have everything clearly pictured in your mind,
720 proceed in the following order:
721 First, generate the configuration files (@file{tinc.conf}, your host configuration file, @file{tinc-up} and perhaps @file{tinc-down}).
722 Then generate the keypairs.
723 Finally, distribute the host configuration files.
724 These steps are described in the subsections below.
727 @c ==================================================================
728 @node Multiple networks
729 @section Multiple networks
731 @cindex multiple networks
733 In order to allow you to run more than one tinc daemon on one computer,
734 for instance if your computer is part of more than one VPN,
735 you can assign a @var{netname} to your VPN.
736 It is not required if you only run one tinc daemon,
737 it doesn't even have to be the same on all the sites of your VPN,
738 but it is recommended that you choose one anyway.
740 We will asume you use a netname throughout this document.
741 This means that you call tincd with the -n argument,
742 which will assign a netname to this daemon.
744 The effect of this is that the daemon will set its configuration
745 root to @file{@value{sysconfdir}/tinc/@var{netname}/}, where @var{netname} is your argument to the -n
746 option. You'll notice that it appears in syslog as @file{tinc.@var{netname}}.
748 However, it is not strictly necessary that you call tinc with the -n
749 option. In this case, the network name would just be empty, and it will
750 be used as such. tinc now looks for files in @file{@value{sysconfdir}/tinc/}, instead of
751 @file{@value{sysconfdir}/tinc/@var{netname}/}; the configuration file should be @file{@value{sysconfdir}/tinc/tinc.conf},
752 and the host configuration files are now expected to be in @file{@value{sysconfdir}/tinc/hosts/}.
754 But it is highly recommended that you use this feature of tinc, because
755 it will be so much clearer whom your daemon talks to. Hence, we will
756 assume that you use it.
759 @c ==================================================================
760 @node How connections work
761 @section How connections work
763 When tinc starts up, it parses the command-line options and then
764 reads in the configuration file tinc.conf.
765 If it sees one or more `ConnectTo' values pointing to other tinc daemons in that file,
766 it will try to connect to those other daemons.
767 Whether this succeeds or not and whether `ConnectTo' is specified or not,
768 tinc will listen for incoming connection from other deamons.
769 If you did specify a `ConnectTo' value and the other side is not responding,
770 tinc will keep retrying.
771 This means that once started, tinc will stay running until you tell it to stop,
772 and failures to connect to other tinc daemons will not stop your tinc daemon
773 for trying again later.
774 This means you don't have to intervene if there are temporary network problems.
778 There is no real distinction between a server and a client in tinc.
779 If you wish, you can view a tinc daemon without a `ConnectTo' value as a server,
780 and one which does specify such a value as a client.
781 It does not matter if two tinc daemons have a `ConnectTo' value pointing to each other however.
784 @c ==================================================================
785 @node Configuration files
786 @section Configuration files
788 The actual configuration of the daemon is done in the file
789 @file{@value{sysconfdir}/tinc/@var{netname}/tinc.conf} and at least one other file in the directory
790 @file{@value{sysconfdir}/tinc/@var{netname}/hosts/}.
792 These file consists of comments (lines started with a #) or assignments
799 The variable names are case insensitive, and any spaces, tabs, newlines
800 and carriage returns are ignored. Note: it is not required that you put
801 in the `=' sign, but doing so improves readability. If you leave it
802 out, remember to replace it with at least one space character.
804 In this section all valid variables are listed in alphabetical order.
805 The default value is given between parentheses,
806 other comments are between square brackets.
809 * Main configuration variables::
810 * Host configuration variables::
816 @c ==================================================================
817 @node Main configuration variables
818 @subsection Main configuration variables
821 @cindex AddressFamily
822 @item AddressFamily = <ipv4|ipv6|any> (any)
823 This option affects the address family of listening and outgoing sockets.
824 If any is selected, then depending on the operating system
825 both IPv4 and IPv6 or just IPv6 listening sockets will be created.
827 @cindex BindToAddress
828 @item BindToAddress = <@var{address}> [experimental]
829 If your computer has more than one IPv4 or IPv6 address, tinc
830 will by default listen on all of them for incoming connections.
831 It is possible to bind only to a single address with this variable.
833 This option may not work on all platforms.
835 @cindex BindToInterface
836 @item BindToInterface = <@var{interface}> [experimental]
837 If you have more than one network interface in your computer, tinc will
838 by default listen on all of them for incoming connections. It is
839 possible to bind tinc to a single interface like eth0 or ppp0 with this
842 This option may not work on all platforms.
845 @item BlockingTCP = <yes|no> (no) [experimental]
846 This options selects whether TCP connections, when established, should use blocking writes.
847 When turned off, tinc will never block when a TCP connection becomes congested,
848 but will have to terminate that connection instead.
849 If turned on, tinc will not terminate connections but will block,
850 thereby unable to process data to/from other connections.
851 Turn this option on if you also use TCPOnly and tinc terminates connections frequently.
854 @item ConnectTo = <@var{name}>
855 Specifies which other tinc daemon to connect to on startup.
856 Multiple ConnectTo variables may be specified,
857 in which case outgoing connections to each specified tinc daemon are made.
858 The names should be known to this tinc daemon
859 (i.e., there should be a host configuration file for the name on the ConnectTo line).
861 If you don't specify a host with ConnectTo,
862 tinc won't try to connect to other daemons at all,
863 and will instead just listen for incoming connections.
866 @item Device = <@var{device}> (@file{/dev/tap0}, @file{/dev/net/tun} or other depending on platform)
867 The virtual network device to use.
868 Tinc will automatically detect what kind of device it is.
869 Note that you can only use one device per daemon.
870 Under Windows, use @var{Interface} instead of @var{Device}.
871 Note that you can only use one device per daemon.
872 See also @ref{Device files}.
875 @item Hostnames = <yes|no> (no)
876 This option selects whether IP addresses (both real and on the VPN)
877 should be resolved. Since DNS lookups are blocking, it might affect
878 tinc's efficiency, even stopping the daemon for a few seconds everytime
879 it does a lookup if your DNS server is not responding.
881 This does not affect resolving hostnames to IP addresses from the
885 @item Interface = <@var{interface}>
886 Defines the name of the interface corresponding to the virtual network device.
887 Depending on the operating system and the type of device this may or may not actually set the name of the interface.
888 Under Windows, this variable is used to select which network interface will be used.
889 If you specified a Device, this variable is almost always already correctly set.
892 @item Mode = <router|switch|hub> (router)
893 This option selects the way packets are routed to other daemons.
899 variables in the host configuration files will be used to form a routing table.
900 Only unicast packets of routable protocols (IPv4 and IPv6) are supported in this mode.
902 This is the default mode, and unless you really know you need another mode, don't change it.
906 In this mode the MAC addresses of the packets on the VPN will be used to
907 dynamically create a routing table just like an Ethernet switch does.
908 Unicast, multicast and broadcast packets of every protocol that runs over Ethernet are supported in this mode
909 at the cost of frequent broadcast ARP requests and routing table updates.
911 This mode is primarily useful if you want to bridge Ethernet segments.
915 This mode is almost the same as the switch mode, but instead
916 every packet will be broadcast to the other daemons
917 while no routing table is managed.
921 @item KeyExpire = <@var{seconds}> (3600)
922 This option controls the time the encryption keys used to encrypt the data
923 are valid. It is common practice to change keys at regular intervals to
924 make it even harder for crackers, even though it is thought to be nearly
925 impossible to crack a single key.
928 @item MACExpire = <@var{seconds}> (600)
929 This option controls the amount of time MAC addresses are kept before they are removed.
930 This only has effect when Mode is set to "switch".
933 @item Name = <@var{name}> [required]
934 This is a symbolic name for this connection. It can be anything
937 @item PingTimeout = <@var{seconds}> (60)
938 The number of seconds of inactivity that tinc will wait before sending a
939 probe to the other end. If that other end doesn't answer within that
940 same amount of seconds, the connection is terminated, and the others
941 will be notified of this.
943 @cindex PriorityInheritance
944 @item PriorityInheritance = <yes|no> (no) [experimental]
945 When this option is enabled the value of the TOS field of tunneled IPv4 packets
946 will be inherited by the UDP packets that are sent out.
949 @item PrivateKey = <@var{key}> [obsolete]
950 This is the RSA private key for tinc. However, for safety reasons it is
951 advised to store private keys of any kind in separate files. This prevents
952 accidental eavesdropping if you are editting the configuration file.
954 @cindex PrivateKeyFile
955 @item PrivateKeyFile = <@var{path}> (@file{@value{sysconfdir}/tinc/@var{netname}/rsa_key.priv})
956 This is the full path name of the RSA private key file that was
957 generated by @samp{tincd --generate-keys}. It must be a full path, not a
960 Note that there must be exactly one of PrivateKey
962 specified in the configuration file.
965 @item TunnelServer = <yes|no> (no) [experimental]
966 When this option is enabled tinc will no longer forward information between other tinc daemons,
967 and will only allow nodes and subnets on the VPN which are present in the
968 @file{@value{sysconfdir}/tinc/@var{netname}/hosts/} directory.
973 @c ==================================================================
974 @node Host configuration variables
975 @subsection Host configuration variables
979 @item Address = <@var{IP address}|@var{hostname}> [recommended]
980 This variable is only required if you want to connect to this host. It
981 must resolve to the external IP address where the host can be reached,
982 not the one that is internal to the VPN.
985 @item Cipher = <@var{cipher}> (blowfish)
986 The symmetric cipher algorithm used to encrypt UDP packets.
987 Any cipher supported by OpenSSL is recognized.
988 Furthermore, specifying "none" will turn off packet encryption.
989 It is best to use only those ciphers which support CBC mode.
992 @item Compression = <@var{level}> (0)
993 This option sets the level of compression used for UDP packets.
994 Possible values are 0 (off), 1 (fast zlib) and any integer up to 9 (best zlib),
995 10 (fast lzo) and 11 (best lzo).
998 @item Digest = <@var{digest}> (sha1)
999 The digest algorithm used to authenticate UDP packets.
1000 Any digest supported by OpenSSL is recognized.
1001 Furthermore, specifying "none" will turn off packet authentication.
1003 @cindex IndirectData
1004 @item IndirectData = <yes|no> (no)
1005 This option specifies whether other tinc daemons besides the one you
1006 specified with ConnectTo can make a direct connection to you. This is
1007 especially useful if you are behind a firewall and it is impossible to
1008 make a connection from the outside to your tinc daemon. Otherwise, it
1009 is best to leave this option out or set it to no.
1012 @item MACLength = <@var{bytes}> (4)
1013 The length of the message authentication code used to authenticate UDP packets.
1014 Can be anything from 0
1015 up to the length of the digest produced by the digest algorithm.
1018 @item Port = <@var{port}> (655)
1019 This is the port this tinc daemon listens on.
1020 You can use decimal portnumbers or symbolic names (as listed in @file{/etc/services}).
1023 @item PublicKey = <@var{key}> [obsolete]
1024 This is the RSA public key for this host.
1026 @cindex PublicKeyFile
1027 @item PublicKeyFile = <@var{path}> [obsolete]
1028 This is the full path name of the RSA public key file that was generated
1029 by @samp{tincd --generate-keys}. It must be a full path, not a relative
1033 From version 1.0pre4 on tinc will store the public key directly into the
1034 host configuration file in PEM format, the above two options then are not
1035 necessary. Either the PEM format is used, or exactly
1036 @strong{one of the above two options} must be specified
1037 in each host configuration file, if you want to be able to establish a
1038 connection with that host.
1041 @item Subnet = <@var{address}[/@var{prefixlength}]>
1042 The subnet which this tinc daemon will serve.
1043 Tinc tries to look up which other daemon it should send a packet to by searching the appropiate subnet.
1044 If the packet matches a subnet,
1045 it will be sent to the daemon who has this subnet in his host configuration file.
1046 Multiple subnet lines can be specified for each daemon.
1048 Subnets can either be single MAC, IPv4 or IPv6 addresses,
1049 in which case a subnet consisting of only that single address is assumed,
1050 or they can be a IPv4 or IPv6 network address with a prefixlength.
1051 Shorthand notations are not supported.
1052 For example, IPv4 subnets must be in a form like 192.168.1.0/24,
1053 where 192.168.1.0 is the network address and 24 is the number of bits set in the netmask.
1054 Note that subnets like 192.168.1.1/24 are invalid!
1055 Read a networking HOWTO/FAQ/guide if you don't understand this.
1056 IPv6 subnets are notated like fec0:0:0:1:0:0:0:0/64.
1057 MAC addresses are notated like 0:1a:2b:3c:4d:5e.
1059 @cindex CIDR notation
1060 Prefixlength is the number of bits set to 1 in the netmask part; for
1061 example: netmask 255.255.255.0 would become /24, 255.255.252.0 becomes
1062 /22. This conforms to standard CIDR notation as described in
1063 @uref{ftp://ftp.isi.edu/in-notes/rfc1519.txt, RFC1519}
1066 @item TCPonly = <yes|no> (no) [experimental]
1067 If this variable is set to yes, then the packets are tunnelled over a
1068 TCP connection instead of a UDP connection. This is especially useful
1069 for those who want to run a tinc daemon from behind a masquerading
1070 firewall, or if UDP packet routing is disabled somehow.
1071 Setting this options also implicitly sets IndirectData.
1075 @c ==================================================================
1080 Apart from reading the server and host configuration files,
1081 tinc can also run scripts at certain moments.
1082 Under Windows (not Cygwin), the scripts should have the extension .bat.
1086 @item @value{sysconfdir}/tinc/@var{netname}/tinc-up
1087 This is the most important script.
1088 If it is present it will be executed right after the tinc daemon has been
1089 started and has connected to the virtual network device.
1090 It should be used to set up the corresponding network interface,
1091 but can also be used to start other things.
1092 Under Windows you can use the Network Connections control panel instead of creating this script.
1095 @item @value{sysconfdir}/tinc/@var{netname}/tinc-down
1096 This script is started right before the tinc daemon quits.
1098 @item @value{sysconfdir}/tinc/@var{netname}/hosts/@var{host}-up
1099 This script is started when the tinc daemon with name @var{host} becomes reachable.
1101 @item @value{sysconfdir}/tinc/@var{netname}/hosts/@var{host}-down
1102 This script is started when the tinc daemon with name @var{host} becomes unreachable.
1104 @item @value{sysconfdir}/tinc/@var{netname}/subnet-up
1105 This script is started when a Subnet becomes reachable.
1106 The Subnet and the node it belongs to are passed in environment variables.
1108 @item @value{sysconfdir}/tinc/@var{netname}/subnet-down
1109 This script is started when a Subnet becomes unreachable.
1112 @cindex environment variables
1113 The scripts are started without command line arguments,
1114 but can make use of certain environment variables.
1115 Under UNIX like operating systems the names of environment variables must be preceded by a $ in scripts.
1116 Under Windows, in @file{.bat} files, they have to be put between % signs.
1121 If a netname was specified, this environment variable contains it.
1125 Contains the name of this tinc daemon.
1129 Contains the name of the virtual network device that tinc uses.
1133 Contains the name of the virtual network interface that tinc uses.
1134 This should be used for commands like ifconfig.
1138 When a host becomes (un)reachable, this is set to its name.
1139 If a subnet becomes (un)reachable, this is set to the owner of that subnet.
1141 @cindex REMOTEADDRESS
1143 When a host becomes (un)reachable, this is set to its real address.
1147 When a host becomes (un)reachable,
1148 this is set to the port number it uses for communication with other tinc daemons.
1152 When a subnet becomes (un)reachable, this is set to the subnet.
1157 @c ==================================================================
1158 @node How to configure
1159 @subsection How to configure
1161 @subsubheading Step 1. Creating the main configuration file
1163 The main configuration file will be called @file{@value{sysconfdir}/tinc/@var{netname}/tinc.conf}.
1164 Adapt the following example to create a basic configuration file:
1167 Name = @var{yourname}
1168 Device = @file{/dev/tap0}
1171 Then, if you know to which other tinc daemon(s) yours is going to connect,
1172 add `ConnectTo' values.
1174 @subsubheading Step 2. Creating your host configuration file
1176 If you added a line containing `Name = yourname' in the main configuarion file,
1177 you will need to create a host configuration file @file{@value{sysconfdir}/tinc/@var{netname}/hosts/yourname}.
1178 Adapt the following example to create a host configuration file:
1181 Address = your.real.hostname.org
1182 Subnet = 192.168.1.0/24
1185 You can also use an IP address instead of a hostname.
1186 The `Subnet' specifies the address range that is local for @emph{your part of the VPN only}.
1187 If you have multiple address ranges you can specify more than one `Subnet'.
1188 You might also need to add a `Port' if you want your tinc daemon to run on a different port number than the default (655).
1191 @c ==================================================================
1192 @node Generating keypairs
1193 @section Generating keypairs
1195 @cindex key generation
1196 Now that you have already created the main configuration file and your host configuration file,
1197 you can easily create a public/private keypair by entering the following command:
1200 tincd -n @var{netname} -K
1203 Tinc will generate a public and a private key and ask you where to put them.
1204 Just press enter to accept the defaults.
1207 @c ==================================================================
1208 @node Network interfaces
1209 @section Network interfaces
1211 Before tinc can start transmitting data over the tunnel, it must
1212 set up the virtual network interface.
1214 First, decide which IP addresses you want to have associated with these
1215 devices, and what network mask they must have.
1217 Tinc will open a virtual network device (@file{/dev/tun}, @file{/dev/tap0} or similar),
1218 which will also create a network interface called something like @samp{tun0}, @samp{tap0}.
1219 If you are using the Linux tun/tap driver, the network interface will by default have the same name as the @var{netname}.
1220 Under Windows you can change the name of the network interface from the Network Connections control panel.
1223 You can configure the network interface by putting ordinary ifconfig, route, and other commands
1224 to a script named @file{@value{sysconfdir}/tinc/@var{netname}/tinc-up}.
1225 When tinc starts, this script will be executed. When tinc exits, it will execute the script named
1226 @file{@value{sysconfdir}/tinc/@var{netname}/tinc-down}, but normally you don't need to create that script.
1228 An example @file{tinc-up} script:
1232 ifconfig $INTERFACE 192.168.1.1 netmask 255.255.0.0
1235 This script gives the interface an IP address and a netmask.
1236 The kernel will also automatically add a route to this interface, so normally you don't need
1237 to add route commands to the @file{tinc-up} script.
1238 The kernel will also bring the interface up after this command.
1240 The netmask is the mask of the @emph{entire} VPN network, not just your
1243 The exact syntax of the ifconfig and route commands differs from platform to platform.
1244 You can look up the commands for setting addresses and adding routes in @ref{Platform specific information},
1245 but it is best to consult the manpages of those utilities on your platform.
1248 @c ==================================================================
1249 @node Example configuration
1250 @section Example configuration
1254 Imagine the following situation. Branch A of our example `company' wants to connect
1255 three branch offices in B, C and D using the Internet. All four offices
1256 have a 24/7 connection to the Internet.
1258 A is going to serve as the center of the network. B and C will connect
1259 to A, and D will connect to C. Each office will be assigned their own IP
1263 A: net 10.1.0.0 mask 255.255.0.0 gateway 10.1.54.1 internet IP 1.2.3.4
1264 B: net 10.2.0.0 mask 255.255.0.0 gateway 10.2.1.12 internet IP 2.3.4.5
1265 C: net 10.3.0.0 mask 255.255.0.0 gateway 10.3.69.254 internet IP 3.4.5.6
1266 D: net 10.4.0.0 mask 255.255.0.0 gateway 10.4.3.32 internet IP 4.5.6.7
1269 Here, ``gateway'' is the VPN IP address of the machine that is running the
1270 tincd, and ``internet IP'' is the IP address of the firewall, which does not
1271 need to run tincd, but it must do a port forwarding of TCP and UDP on port
1272 655 (unless otherwise configured).
1274 In this example, it is assumed that eth0 is the interface that points to
1275 the inner (physical) LAN of the office, although this could also be the
1276 same as the interface that leads to the Internet. The configuration of
1277 the real interface is also shown as a comment, to give you an idea of
1278 how these example host is set up. All branches use the netname `company'
1279 for this particular VPN.
1281 @subsubheading For Branch A
1283 @emph{BranchA} would be configured like this:
1285 In @file{@value{sysconfdir}/tinc/company/tinc-up}:
1288 # Real interface of internal network:
1289 # ifconfig eth0 10.1.54.1 netmask 255.255.0.0
1291 ifconfig $INTERFACE 10.1.54.1 netmask 255.0.0.0
1294 and in @file{@value{sysconfdir}/tinc/company/tinc.conf}:
1301 On all hosts, @file{@value{sysconfdir}/tinc/company/hosts/BranchA} contains:
1304 Subnet = 10.1.0.0/16
1307 -----BEGIN RSA PUBLIC KEY-----
1309 -----END RSA PUBLIC KEY-----
1312 Note that the IP addresses of eth0 and tap0 are the same.
1313 This is quite possible, if you make sure that the netmasks of the interfaces are different.
1314 It is in fact recommended to give give both real internal network interfaces and tap interfaces the same IP address,
1315 since that will make things a lot easier to remember and set up.
1318 @subsubheading For Branch B
1320 In @file{@value{sysconfdir}/tinc/company/tinc-up}:
1323 # Real interface of internal network:
1324 # ifconfig eth0 10.2.43.8 netmask 255.255.0.0
1326 ifconfig $INTERFACE 10.2.1.12 netmask 255.0.0.0
1329 and in @file{@value{sysconfdir}/tinc/company/tinc.conf}:
1336 Note here that the internal address (on eth0) doesn't have to be the
1337 same as on the tap0 device. Also, ConnectTo is given so that no-one can
1338 connect to this node.
1340 On all hosts, in @file{@value{sysconfdir}/tinc/company/hosts/BranchB}:
1343 Subnet = 10.2.0.0/16
1346 -----BEGIN RSA PUBLIC KEY-----
1348 -----END RSA PUBLIC KEY-----
1352 @subsubheading For Branch C
1354 In @file{@value{sysconfdir}/tinc/company/tinc-up}:
1357 # Real interface of internal network:
1358 # ifconfig eth0 10.3.69.254 netmask 255.255.0.0
1360 ifconfig $INTERFACE 10.3.69.254 netmask 255.0.0.0
1363 and in @file{@value{sysconfdir}/tinc/company/tinc.conf}:
1371 C already has another daemon that runs on port 655, so they have to
1372 reserve another port for tinc. It knows the portnumber it has to listen on
1373 from it's own host configuration file.
1375 On all hosts, in @file{@value{sysconfdir}/tinc/company/hosts/BranchC}:
1379 Subnet = 10.3.0.0/16
1382 -----BEGIN RSA PUBLIC KEY-----
1384 -----END RSA PUBLIC KEY-----
1388 @subsubheading For Branch D
1390 In @file{@value{sysconfdir}/tinc/company/tinc-up}:
1393 # Real interface of internal network:
1394 # ifconfig eth0 10.4.3.32 netmask 255.255.0.0
1396 ifconfig $INTERFACE 10.4.3.32 netmask 255.0.0.0
1399 and in @file{@value{sysconfdir}/tinc/company/tinc.conf}:
1404 Device = /dev/net/tun
1407 D will be connecting to C, which has a tincd running for this network on
1408 port 2000. It knows the port number from the host configuration file.
1409 Also note that since D uses the tun/tap driver, the network interface
1410 will not be called `tun' or `tap0' or something like that, but will
1411 have the same name as netname.
1413 On all hosts, in @file{@value{sysconfdir}/tinc/company/hosts/BranchD}:
1416 Subnet = 10.4.0.0/16
1419 -----BEGIN RSA PUBLIC KEY-----
1421 -----END RSA PUBLIC KEY-----
1424 @subsubheading Key files
1426 A, B, C and D all have generated a public/private keypair with the following command:
1432 The private key is stored in @file{@value{sysconfdir}/tinc/company/rsa_key.priv},
1433 the public key is put into the host configuration file in the @file{@value{sysconfdir}/tinc/company/hosts/} directory.
1434 During key generation, tinc automatically guesses the right filenames based on the -n option and
1435 the Name directive in the @file{tinc.conf} file (if it is available).
1437 @subsubheading Starting
1439 After each branch has finished configuration and they have distributed
1440 the host configuration files amongst them, they can start their tinc daemons.
1441 They don't necessarily have to wait for the other branches to have started
1442 their daemons, tinc will try connecting until they are available.
1445 @c ==================================================================
1447 @chapter Running tinc
1449 If everything else is done, you can start tinc by typing the following command:
1452 tincd -n @var{netname}
1456 Tinc will detach from the terminal and continue to run in the background like a good daemon.
1457 If there are any problems however you can try to increase the debug level
1458 and look in the syslog to find out what the problems are.
1464 * Solving problems::
1466 * Sending bug reports::
1470 @c ==================================================================
1471 @node Runtime options
1472 @section Runtime options
1474 Besides the settings in the configuration file, tinc also accepts some
1475 command line options.
1477 @cindex command line
1478 @cindex runtime options
1482 @item -c, --config=@var{path}
1483 Read configuration options from the directory @var{path}. The default is
1484 @file{@value{sysconfdir}/tinc/@var{netname}/}.
1486 @item -D, --no-detach
1487 Don't fork and detach.
1488 This will also disable the automatic restart mechanism for fatal errors.
1491 @item -d, --debug=@var{level}
1492 Set debug level to @var{level}. The higher the debug level, the more gets
1493 logged. Everything goes via syslog.
1495 @item -k, --kill[=@var{signal}]
1496 Attempt to kill a running tincd (optionally with the specified @var{signal} instead of SIGTERM) and exit.
1497 Use it in conjunction with the -n option to make sure you kill the right tinc daemon.
1498 Under native Windows the optional argument is ignored,
1499 the service will always be stopped and removed.
1501 @item -n, --net=@var{netname}
1502 Use configuration for net @var{netname}. @xref{Multiple networks}.
1504 @item -K, --generate-keys[=@var{bits}]
1505 Generate public/private keypair of @var{bits} length. If @var{bits} is not specified,
1506 1024 is the default. tinc will ask where you want to store the files,
1507 but will default to the configuration directory (you can use the -c or -n option
1508 in combination with -K). After that, tinc will quit.
1511 Lock tinc into main memory.
1512 This will prevent sensitive data like shared private keys to be written to the system swap files/partitions.
1514 @item --logfile[=@var{file}]
1515 Write log entries to a file instead of to the system logging facility.
1516 If @var{file} is omitted, the default is @file{@value{localstatedir}/log/tinc.@var{netname}.log}.
1518 @item --pidfile=@var{file}
1519 Write PID to @var{file} instead of @file{@value{localstatedir}/run/tinc.@var{netname}.pid}.
1521 @item --bypass-security
1522 Disables encryption and authentication.
1523 Only useful for debugging.
1526 Display a short reminder of these runtime options and terminate.
1529 Output version information and exit.
1533 @c ==================================================================
1538 You can also send the following signals to a running tincd process:
1544 Forces tinc to try to connect to all uplinks immediately.
1545 Usually tinc attempts to do this itself,
1546 but increases the time it waits between the attempts each time it failed,
1547 and if tinc didn't succeed to connect to an uplink the first time after it started,
1548 it defaults to the maximum time of 15 minutes.
1551 Partially rereads configuration files.
1552 Connections to hosts whose host config file are removed are closed.
1553 New outgoing connections specified in @file{tinc.conf} will be made.
1556 Temporarily increases debug level to 5.
1557 Send this signal again to revert to the original level.
1560 Dumps the connection list to syslog.
1563 Dumps virtual network device statistics, all known nodes, edges and subnets to syslog.
1566 Purges all information remembered about unreachable nodes.
1570 @c ==================================================================
1572 @section Debug levels
1574 @cindex debug levels
1575 The tinc daemon can send a lot of messages to the syslog.
1576 The higher the debug level, the more messages it will log.
1577 Each level inherits all messages of the previous level:
1583 This will log a message indicating tinc has started along with a version number.
1584 It will also log any serious error.
1587 This will log all connections that are made with other tinc daemons.
1590 This will log status and error messages from scripts and other tinc daemons.
1593 This will log all requests that are exchanged with other tinc daemons. These include
1594 authentication, key exchange and connection list updates.
1597 This will log a copy of everything received on the meta socket.
1600 This will log all network traffic over the virtual private network.
1604 @c ==================================================================
1605 @node Solving problems
1606 @section Solving problems
1608 If tinc starts without problems, but if the VPN doesn't work, you will have to find the cause of the problem.
1609 The first thing to do is to start tinc with a high debug level in the foreground,
1610 so you can directly see everything tinc logs:
1613 tincd -n @var{netname} -d5 -D
1616 If tinc does not log any error messages, then you might want to check the following things:
1619 @item @file{tinc-up} script
1620 Does this script contain the right commands?
1621 Normally you must give the interface the address of this host on the VPN, and the netmask must be big enough so that the entire VPN is covered.
1624 Does the Subnet (or Subnets) in the host configuration file of this host match the portion of the VPN that belongs to this host?
1626 @item Firewalls and NATs
1627 Do you have a firewall or a NAT device (a masquerading firewall or perhaps an ADSL router that performs masquerading)?
1628 If so, check that it allows TCP and UDP traffic on port 655.
1629 If it masquerades and the host running tinc is behind it, make sure that it forwards TCP and UDP traffic to port 655 to the host running tinc.
1630 You can add @samp{TCPOnly = yes} to your host config file to force tinc to only use a single TCP connection,
1631 this works through most firewalls and NATs.
1636 @c ==================================================================
1637 @node Error messages
1638 @section Error messages
1640 What follows is a list of the most common error messages you might find in the logs.
1641 Some of them will only be visible if the debug level is high enough.
1644 @item Could not open /dev/tap0: No such device
1647 @item You forgot to `modprobe netlink_dev' or `modprobe ethertap'.
1648 @item You forgot to compile `Netlink device emulation' in the kernel.
1651 @item Can't write to /dev/net/tun: No such device
1654 @item You forgot to `modprobe tun'.
1655 @item You forgot to compile `Universal TUN/TAP driver' in the kernel.
1656 @item The tun device is located somewhere else in @file{/dev/}.
1659 @item Network address and prefix length do not match!
1662 @item The Subnet field must contain a @emph{network} address, trailing bits should be 0.
1663 @item If you only want to use one IP address, set the netmask to /32.
1666 @item Error reading RSA key file `rsa_key.priv': No such file or directory
1669 @item You forgot to create a public/private keypair.
1670 @item Specify the complete pathname to the private key file with the @samp{PrivateKeyFile} option.
1673 @item Warning: insecure file permissions for RSA private key file `rsa_key.priv'!
1676 @item The private key file is readable by users other than root.
1677 Use chmod to correct the file permissions.
1680 @item Creating metasocket failed: Address family not supported
1683 @item By default tinc tries to create both IPv4 and IPv6 sockets.
1684 On some platforms this might not be implemented.
1685 If the logs show @samp{Ready} later on, then at least one metasocket was created,
1686 and you can ignore this message.
1687 You can add @samp{AddressFamily = ipv4} to @file{tinc.conf} to prevent this from happening.
1690 @item Cannot route packet: unknown IPv4 destination 1.2.3.4
1693 @item You try to send traffic to a host on the VPN for which no Subnet is known.
1694 @item If it is a broadcast address (ending in .255), it probably is a samba server or a Windows host sending broadcast packets.
1698 @item Cannot route packet: ARP request for unknown address 1.2.3.4
1701 @item You try to send traffic to a host on the VPN for which no Subnet is known.
1704 @item Packet with destination 1.2.3.4 is looping back to us!
1707 @item Something is not configured right. Packets are being sent out to the
1708 virtual network device, but according to the Subnet directives in your host configuration
1709 file, those packets should go to your own host. Most common mistake is that
1710 you have a Subnet line in your host configuration file with a prefix length which is
1711 just as large as the prefix of the virtual network interface. The latter should in almost all
1712 cases be larger. Rethink your configuration.
1713 Note that you will only see this message if you specified a debug
1714 level of 5 or higher!
1715 @item Chances are that a @samp{Subnet = ...} line in the host configuration file of this tinc daemon is wrong.
1716 Change it to a subnet that is accepted locally by another interface,
1717 or if that is not the case, try changing the prefix length into /32.
1720 @item Node foo (1.2.3.4) is not reachable
1723 @item Node foo does not have a connection anymore, its tinc daemon is not running or its connection to the Internet is broken.
1726 @item Received UDP packet from unknown source 1.2.3.4 (port 12345)
1729 @item If you see this only sporadically, it is harmless and caused by a node sending packets using an old key.
1730 @item If you see this often and another node is not reachable anymore, then a NAT (masquerading firewall) is changing the source address of UDP packets.
1731 You can add @samp{TCPOnly = yes} to host configuration files to force all VPN traffic to go over a TCP connection.
1734 @item Got bad/bogus/unauthorized REQUEST from foo (1.2.3.4 port 12345)
1737 @item Node foo does not have the right public/private keypair.
1738 Generate new keypairs and distribute them again.
1739 @item An attacker tries to gain access to your VPN.
1740 @item A network error caused corruption of metadata sent from foo.
1745 @c ==================================================================
1746 @node Sending bug reports
1747 @section Sending bug reports
1749 If you really can't find the cause of a problem, or if you suspect tinc is not working right,
1750 you can send us a bugreport, see @ref{Contact information}.
1751 Be sure to include the following information in your bugreport:
1754 @item A clear description of what you are trying to achieve and what the problem is.
1755 @item What platform (operating system, version, hardware architecture) and which version of tinc you use.
1756 @item If compiling tinc fails, a copy of @file{config.log} and the error messages you get.
1757 @item Otherwise, a copy of @file{tinc.conf}, @file{tinc-up} and all files in the @file{hosts/} directory.
1758 @item The output of the commands @samp{ifconfig -a} and @samp{route -n} (or @samp{netstat -rn} if that doesn't work).
1759 @item The output of any command that fails to work as it should (like ping or traceroute).
1762 @c ==================================================================
1763 @node Technical information
1764 @chapter Technical information
1769 * The meta-protocol::
1774 @c ==================================================================
1775 @node The connection
1776 @section The connection
1779 Tinc is a daemon that takes VPN data and transmit that to another host
1780 computer over the existing Internet infrastructure.
1784 * The meta-connection::
1788 @c ==================================================================
1789 @node The UDP tunnel
1790 @subsection The UDP tunnel
1792 @cindex virtual network device
1794 The data itself is read from a character device file, the so-called
1795 @emph{virtual network device}. This device is associated with a network
1796 interface. Any data sent to this interface can be read from the device,
1797 and any data written to the device gets sent from the interface.
1798 There are two possible types of virtual network devices:
1799 `tun' style, which are point-to-point devices which can only handle IPv4 and/or IPv6 packets,
1800 and `tap' style, which are Ethernet devices and handle complete Ethernet frames.
1802 So when tinc reads an Ethernet frame from the device, it determines its
1803 type. When tinc is in it's default routing mode, it can handle IPv4 and IPv6
1804 packets. Depending on the Subnet lines, it will send the packets off to their destination IP address.
1805 In the `switch' and `hub' mode, tinc will use broadcasts and MAC address discovery
1806 to deduce the destination of the packets.
1807 Since the latter modes only depend on the link layer information,
1808 any protocol that runs over Ethernet is supported (for instance IPX and Appletalk).
1809 However, only `tap' style devices provide this information.
1811 After the destination has been determined,
1812 the packet will be compressed (optionally),
1813 a sequence number will be added to the packet,
1814 the packet will then be encrypted
1815 and a message authentication code will be appended.
1817 @cindex encapsulating
1819 When that is done, time has come to actually transport the
1820 packet to the destination computer. We do this by sending the packet
1821 over an UDP connection to the destination host. This is called
1822 @emph{encapsulating}, the VPN packet (though now encrypted) is
1823 encapsulated in another IP datagram.
1825 When the destination receives this packet, the same thing happens, only
1826 in reverse. So it checks the message authentication code, decrypts the contents of the UDP datagram,
1827 checks the sequence number
1828 and writes the decrypted information to its own virtual network device.
1830 If the virtual network device is a `tun' device (a point-to-point tunnel),
1831 there is no problem for the kernel to accept a packet.
1832 However, if it is a `tap' device (this is the only available type on FreeBSD),
1833 the destination MAC address must match that of the virtual network interface.
1834 If tinc is in it's default routing mode, ARP does not work, so the correct destination MAC
1835 can not be known by the sending host.
1836 Tinc solves this by letting the receiving end detect the MAC address of its own virtual network interface
1837 and overwriting the destination MAC address of the received packet.
1839 In switch or hub modes ARP does work so the sender already knows the correct destination MAC address.
1840 In those modes every interface should have a unique MAC address, so make sure they are not the same.
1841 Because switch and hub modes rely on MAC addresses to function correctly,
1842 these modes cannot be used on the following operating systems which don't have a `tap' style virtual network device:
1843 OpenBSD, NetBSD, Darwin and Solaris.
1846 @c ==================================================================
1847 @node The meta-connection
1848 @subsection The meta-connection
1850 Having only a UDP connection available is not enough. Though suitable
1851 for transmitting data, we want to be able to reliably send other
1852 information, such as routing and session key information to somebody.
1855 TCP is a better alternative, because it already contains protection
1856 against information being lost, unlike UDP.
1858 So we establish two connections. One for the encrypted VPN data, and one
1859 for other information, the meta-data. Hence, we call the second
1860 connection the meta-connection. We can now be sure that the
1861 meta-information doesn't get lost on the way to another computer.
1863 @cindex data-protocol
1864 @cindex meta-protocol
1865 Like with any communication, we must have a protocol, so that everybody
1866 knows what everything stands for, and how she should react. Because we
1867 have two connections, we also have two protocols. The protocol used for
1868 the UDP data is the ``data-protocol,'' the other one is the
1871 The reason we don't use TCP for both protocols is that UDP is much
1872 better for encapsulation, even while it is less reliable. The real
1873 problem is that when TCP would be used to encapsulate a TCP stream
1874 that's on the private network, for every packet sent there would be
1875 three ACKs sent instead of just one. Furthermore, if there would be
1876 a timeout, both TCP streams would sense the timeout, and both would
1877 start re-sending packets.
1880 @c ==================================================================
1881 @node The meta-protocol
1882 @section The meta-protocol
1884 The meta protocol is used to tie all tinc daemons together, and
1885 exchange information about which tinc daemon serves which virtual
1888 The meta protocol consists of requests that can be sent to the other
1889 side. Each request has a unique number and several parameters. All
1890 requests are represented in the standard ASCII character set. It is
1891 possible to use tools such as telnet or netcat to connect to a tinc
1892 daemon started with the --bypass-security option
1893 and to read and write requests by hand, provided that one
1894 understands the numeric codes sent.
1896 The authentication scheme is described in @ref{Authentication protocol}. After a
1897 successful authentication, the server and the client will exchange all the
1898 information about other tinc daemons and subnets they know of, so that both
1899 sides (and all the other tinc daemons behind them) have their information
1906 ------------------------------------------------------------------
1907 ADD_EDGE node1 node2 21.32.43.54 655 222 0
1908 | | | | | +-> options
1909 | | | | +----> weight
1910 | | | +--------> UDP port of node2
1911 | | +----------------> real address of node2
1912 | +-------------------------> name of destination node
1913 +-------------------------------> name of source node
1915 ADD_SUBNET node 192.168.1.0/24
1916 | | +--> prefixlength
1917 | +--------> network address
1918 +------------------> owner of this subnet
1919 ------------------------------------------------------------------
1922 The ADD_EDGE messages are to inform other tinc daemons that a connection between
1923 two nodes exist. The address of the destination node is available so that
1924 VPN packets can be sent directly to that node.
1926 The ADD_SUBNET messages inform other tinc daemons that certain subnets belong
1927 to certain nodes. tinc will use it to determine to which node a VPN packet has
1934 ------------------------------------------------------------------
1935 DEL_EDGE node1 node2
1936 | +----> name of destination node
1937 +----------> name of source node
1939 DEL_SUBNET node 192.168.1.0/24
1940 | | +--> prefixlength
1941 | +--------> network address
1942 +------------------> owner of this subnet
1943 ------------------------------------------------------------------
1946 In case a connection between two daemons is closed or broken, DEL_EDGE messages
1947 are sent to inform the other daemons of that fact. Each daemon will calculate a
1948 new route to the the daemons, or mark them unreachable if there isn't any.
1955 ------------------------------------------------------------------
1956 REQ_KEY origin destination
1957 | +--> name of the tinc daemon it wants the key from
1958 +----------> name of the daemon that wants the key
1960 ANS_KEY origin destination 4ae0b0a82d6e0078 91 64 4
1961 | | \______________/ | | +--> MAC length
1962 | | | | +-----> digest algorithm
1963 | | | +--------> cipher algorithm
1964 | | +--> 128 bits key
1965 | +--> name of the daemon that wants the key
1966 +----------> name of the daemon that uses this key
1969 +--> daemon that has changed it's packet key
1970 ------------------------------------------------------------------
1973 The keys used to encrypt VPN packets are not sent out directly. This is
1974 because it would generate a lot of traffic on VPNs with many daemons, and
1975 chances are that not every tinc daemon will ever send a packet to every
1976 other daemon. Instead, if a daemon needs a key it sends a request for it
1977 via the meta connection of the nearest hop in the direction of the
1984 ------------------------------------------------------------------
1987 ------------------------------------------------------------------
1990 There is also a mechanism to check if hosts are still alive. Since network
1991 failures or a crash can cause a daemon to be killed without properly
1992 shutting down the TCP connection, this is necessary to keep an up to date
1993 connection list. PINGs are sent at regular intervals, except when there
1994 is also some other traffic. A little bit of salt (random data) is added
1995 with each PING and PONG message, to make sure that long sequences of PING/PONG
1996 messages without any other traffic won't result in known plaintext.
1998 This basically covers what is sent over the meta connection by tinc.
2001 @c ==================================================================
2007 Tinc got its name from ``TINC,'' short for @emph{There Is No Cabal}; the
2008 alleged Cabal was/is an organisation that was said to keep an eye on the
2009 entire Internet. As this is exactly what you @emph{don't} want, we named
2010 the tinc project after TINC.
2013 But in order to be ``immune'' to eavesdropping, you'll have to encrypt
2014 your data. Because tinc is a @emph{Secure} VPN (SVPN) daemon, it does
2015 exactly that: encrypt.
2016 Tinc by default uses blowfish encryption with 128 bit keys in CBC mode, 32 bit
2017 sequence numbers and 4 byte long message authentication codes to make sure
2018 eavesdroppers cannot get and cannot change any information at all from the
2019 packets they can intercept. The encryption algorithm and message authentication
2020 algorithm can be changed in the configuration. The length of the message
2021 authentication codes is also adjustable. The length of the key for the
2022 encryption algorithm is always the default length used by OpenSSL.
2025 * Authentication protocol::
2026 * Encryption of network packets::
2031 @c ==================================================================
2032 @node Authentication protocol
2033 @subsection Authentication protocol
2035 @cindex authentication
2036 A new scheme for authentication in tinc has been devised, which offers some
2037 improvements over the protocol used in 1.0pre2 and 1.0pre3. Explanation is
2047 --------------------------------------------------------------------------
2048 client <attempts connection>
2050 server <accepts connection>
2054 +-------> name of tinc daemon
2058 +-------> name of tinc daemon
2060 client META_KEY 5f0823a93e35b69e...7086ec7866ce582b
2061 \_________________________________/
2062 +-> RSAKEYLEN bits totally random string S1,
2063 encrypted with server's public RSA key
2065 server META_KEY 6ab9c1640388f8f0...45d1a07f8a672630
2066 \_________________________________/
2067 +-> RSAKEYLEN bits totally random string S2,
2068 encrypted with client's public RSA key
2071 - the client will symmetrically encrypt outgoing traffic using S1
2072 - the server will symmetrically encrypt outgoing traffic using S2
2074 client CHALLENGE da02add1817c1920989ba6ae2a49cecbda0
2075 \_________________________________/
2076 +-> CHALLEN bits totally random string H1
2078 server CHALLENGE 57fb4b2ccd70d6bb35a64c142f47e61d57f
2079 \_________________________________/
2080 +-> CHALLEN bits totally random string H2
2082 client CHAL_REPLY 816a86
2083 +-> 160 bits SHA1 of H2
2085 server CHAL_REPLY 928ffe
2086 +-> 160 bits SHA1 of H1
2088 After the correct challenge replies are received, both ends have proved
2089 their identity. Further information is exchanged.
2091 client ACK 655 123 0
2093 | +----> estimated weight
2094 +--------> listening port of client
2096 server ACK 655 321 0
2098 | +----> estimated weight
2099 +--------> listening port of server
2100 --------------------------------------------------------------------------
2103 This new scheme has several improvements, both in efficiency and security.
2105 First of all, the server sends exactly the same kind of messages over the wire
2106 as the client. The previous versions of tinc first authenticated the client,
2107 and then the server. This scheme even allows both sides to send their messages
2108 simultaneously, there is no need to wait for the other to send something first.
2109 This means that any calculations that need to be done upon sending or receiving
2110 a message can also be done in parallel. This is especially important when doing
2111 RSA encryption/decryption. Given that these calculations are the main part of
2112 the CPU time spent for the authentication, speed is improved by a factor 2.
2114 Second, only one RSA encrypted message is sent instead of two. This reduces the
2115 amount of information attackers can see (and thus use for a cryptographic
2116 attack). It also improves speed by a factor two, making the total speedup a
2119 Third, and most important:
2120 The symmetric cipher keys are exchanged first, the challenge is done
2121 afterwards. In the previous authentication scheme, because a man-in-the-middle
2122 could pass the challenge/chal_reply phase (by just copying the messages between
2123 the two real tinc daemons), but no information was exchanged that was really
2124 needed to read the rest of the messages, the challenge/chal_reply phase was of
2125 no real use. The man-in-the-middle was only stopped by the fact that only after
2126 the ACK messages were encrypted with the symmetric cipher. Potentially, it
2127 could even send it's own symmetric key to the server (if it knew the server's
2128 public key) and read some of the metadata the server would send it (it was
2129 impossible for the mitm to read actual network packets though). The new scheme
2130 however prevents this.
2132 This new scheme makes sure that first of all, symmetric keys are exchanged. The
2133 rest of the messages are then encrypted with the symmetric cipher. Then, each
2134 side can only read received messages if they have their private key. The
2135 challenge is there to let the other side know that the private key is really
2136 known, because a challenge reply can only be sent back if the challenge is
2137 decrypted correctly, and that can only be done with knowledge of the private
2140 Fourth: the first thing that is sent via the symmetric cipher encrypted
2141 connection is a totally random string, so that there is no known plaintext (for
2142 an attacker) in the beginning of the encrypted stream.
2145 @c ==================================================================
2146 @node Encryption of network packets
2147 @subsection Encryption of network packets
2150 A data packet can only be sent if the encryption key is known to both
2151 parties, and the connection is activated. If the encryption key is not
2152 known, a request is sent to the destination using the meta connection
2153 to retrieve it. The packet is stored in a queue while waiting for the
2157 The UDP packet containing the network packet from the VPN has the following layout:
2160 ... | IP header | UDP header | seqno | VPN packet | MAC | UDP trailer
2161 \___________________/\_____/
2163 V +---> digest algorithm
2164 Encrypted with symmetric cipher
2167 So, the entire VPN packet is encrypted using a symmetric cipher, including a 32 bits
2168 sequence number that is added in front of the actual VPN packet, to act as a unique
2169 IV for each packet and to prevent replay attacks. A message authentication code
2170 is added to the UDP packet to prevent alteration of packets. By default the
2171 first 4 bytes of the digest are used for this, but this can be changed using
2172 the MACLength configuration variable.
2174 @c ==================================================================
2175 @node Security issues
2176 @subsection Security issues
2178 In August 2000, we discovered the existence of a security hole in all versions
2179 of tinc up to and including 1.0pre2. This had to do with the way we exchanged
2180 keys. Since then, we have been working on a new authentication scheme to make
2181 tinc as secure as possible. The current version uses the OpenSSL library and
2182 uses strong authentication with RSA keys.
2184 On the 29th of December 2001, Jerome Etienne posted a security analysis of tinc
2185 1.0pre4. Due to a lack of sequence numbers and a message authentication code
2186 for each packet, an attacker could possibly disrupt certain network services or
2187 launch a denial of service attack by replaying intercepted packets. The current
2188 version adds sequence numbers and message authentication codes to prevent such
2191 On the 15th of September 2003, Peter Gutmann posted a security analysis of tinc
2192 1.0.1. He argues that the 32 bit sequence number used by tinc is not a good IV,
2193 that tinc's default length of 4 bytes for the MAC is too short, and he doesn't
2194 like tinc's use of RSA during authentication. We do not know of a security hole
2195 in this version of tinc, but tinc's security is not as strong as TLS or IPsec.
2196 We will address these issues in tinc 2.0.
2198 Cryptography is a hard thing to get right. We cannot make any
2199 guarantees. Time, review and feedback are the only things that can
2200 prove the security of any cryptographic product. If you wish to review
2201 tinc or give us feedback, you are stronly encouraged to do so.
2204 @c ==================================================================
2205 @node Platform specific information
2206 @chapter Platform specific information
2209 * Interface configuration::
2213 @c ==================================================================
2214 @node Interface configuration
2215 @section Interface configuration
2217 When configuring an interface, one normally assigns it an address and a
2218 netmask. The address uniquely identifies the host on the network attached to
2219 the interface. The netmask, combined with the address, forms a subnet. It is
2220 used to add a route to the routing table instructing the kernel to send all
2221 packets which fall into that subnet to that interface. Because all packets for
2222 the entire VPN should go to the virtual network interface used by tinc, the
2223 netmask should be such that it encompasses the entire VPN.
2227 @multitable {Darwin (MacOS/X)} {ifconfig route add -bla network address netmask netmask prefixlength interface}
2229 @tab @code{ifconfig} @var{interface} @var{address} @code{netmask} @var{netmask}
2230 @item Linux iproute2
2231 @tab @code{ip addr add} @var{address}@code{/}@var{prefixlength} @code{dev} @var{interface}
2233 @tab @code{ifconfig} @var{interface} @var{address} @code{netmask} @var{netmask}
2235 @tab @code{ifconfig} @var{interface} @var{address} @code{netmask} @var{netmask}
2237 @tab @code{ifconfig} @var{interface} @var{address} @code{netmask} @var{netmask}
2239 @tab @code{ifconfig} @var{interface} @var{address} @code{netmask} @var{netmask}
2240 @item Darwin (MacOS/X)
2241 @tab @code{ifconfig} @var{interface} @var{address} @code{netmask} @var{netmask}
2243 @tab @code{netsh interface ip set address} @var{interface} @code{static} @var{address} @var{netmask}
2249 @multitable {Darwin (MacOS/X)} {ifconfig route add -bla network address netmask netmask prefixlength interface}
2251 @tab @code{ifconfig} @var{interface} @code{add} @var{address}@code{/}@var{prefixlength}
2253 @tab @code{ifconfig} @var{interface} @code{inet6} @var{address} @code{prefixlen} @var{prefixlength}
2255 @tab @code{ifconfig} @var{interface} @code{inet6} @var{address} @code{prefixlen} @var{prefixlength}
2257 @tab @code{ifconfig} @var{interface} @code{inet6} @var{address} @code{prefixlen} @var{prefixlength}
2259 @tab @code{ifconfig} @var{interface} @code{inet6 plumb up}
2261 @tab @code{ifconfig} @var{interface} @code{inet6 addif} @var{address} @var{address}
2262 @item Darwin (MacOS/X)
2263 @tab @code{ifconfig} @var{interface} @code{inet6} @var{address} @code{prefixlen} @var{prefixlength}
2265 @tab @code{netsh interface ipv6 add address} @var{interface} @code{static} @var{address}/@var{prefixlength}
2269 @c ==================================================================
2273 In some cases it might be necessary to add more routes to the virtual network
2274 interface. There are two ways to indicate which interface a packet should go
2275 to, one is to use the name of the interface itself, another way is to specify
2276 the (local) address that is assigned to that interface (@var{local_address}). The
2277 former way is unambiguous and therefore preferable, but not all platforms
2280 Adding routes to IPv4 subnets:
2282 @multitable {Darwin (MacOS/X)} {ifconfig route add -bla network address netmask netmask prefixlength interface}
2284 @tab @code{route add -net} @var{network_address} @code{netmask} @var{netmask} @var{interface}
2285 @item Linux iproute2
2286 @tab @code{ip route add} @var{network_address}@code{/}@var{prefixlength} @code{dev} @var{interface}
2288 @tab @code{route add} @var{network_address}@code{/}@var{prefixlength} @var{local_address}
2290 @tab @code{route add} @var{network_address}@code{/}@var{prefixlength} @var{local_address}
2292 @tab @code{route add} @var{network_address}@code{/}@var{prefixlength} @var{local_address}
2294 @tab @code{route add} @var{network_address}@code{/}@var{prefixlength} @var{local_address} @code{-interface}
2295 @item Darwin (MacOS/X)
2296 @tab @code{route add} @var{network_address}@code{/}@var{prefixlength} @var{local_address}
2298 @tab @code{netsh routing ip add persistentroute} @var{network_address} @var{netmask} @var{interface} @var{local_address}
2301 Adding routes to IPv6 subnets:
2303 @multitable {Darwin (MacOS/X)} {ifconfig route add -bla network address netmask netmask prefixlength interface}
2305 @tab @code{route add -A inet6} @var{network_address}@code{/}@var{prefixlength} @var{interface}
2306 @item Linux iproute2
2307 @tab @code{ip route add} @var{network_address}@code{/}@var{prefixlength} @code{dev} @var{interface}
2309 @tab @code{route add -inet6} @var{network_address}@code{/}@var{prefixlength} @var{local_address}
2311 @tab @code{route add -inet6} @var{network_address} @var{local_address} @code{-prefixlen} @var{prefixlength}
2313 @tab @code{route add -inet6} @var{network_address} @var{local_address} @code{-prefixlen} @var{prefixlength}
2315 @tab @code{route add -inet6} @var{network_address}@code{/}@var{prefixlength} @var{local_address} @code{-interface}
2316 @item Darwin (MacOS/X)
2319 @tab @code{netsh interface ipv6 add route} @var{network address}/@var{prefixlength} @var{interface}
2323 @c ==================================================================
2329 * Contact information::
2334 @c ==================================================================
2335 @node Contact information
2336 @section Contact information
2339 Tinc's website is at @url{http://www.tinc-vpn.org/},
2340 this server is located in the Netherlands.
2343 We have an IRC channel on the FreeNode and OFTC IRC networks. Connect to
2344 @uref{http://www.freenode.net/, irc.freenode.net}
2346 @uref{http://www.oftc.net/, irc.oftc.net}
2347 and join channel #tinc.
2350 @c ==================================================================
2355 @item Ivo Timmermans (zarq) (@email{ivo@@tinc-vpn.org})
2356 @item Guus Sliepen (guus) (@email{guus@@tinc-vpn.org})
2359 We have received a lot of valuable input from users. With their help,
2360 tinc has become the flexible and robust tool that it is today. We have
2361 composed a list of contributions, in the file called @file{THANKS} in
2362 the source distribution.
2365 @c ==================================================================
2367 @unnumbered Concept Index
2369 @c ==================================================================
2373 @c ==================================================================