tinc/doc/tinc.texi

\input texinfo   @c -*-texinfo-*-
@c %**start of header
@setfilename tinc.info
@settitle tinc Manual
@setchapternewpage odd
@c %**end of header

@include tincinclude.texi

@ifinfo
@dircategory Networking tools
@direntry
* tinc: (tinc).              The tinc Manual.
@end direntry

This is the info manual for @value{PACKAGE} version @value{VERSION}, a Virtual Private Network daemon.

Copyright @copyright{} 1998-2017 Ivo Timmermans,
Guus Sliepen <guus@@tinc-vpn.org> and
Wessel Dankers <wsl@@tinc-vpn.org>.

Permission is granted to make and distribute verbatim copies of this
manual provided the copyright notice and this permission notice are
preserved on all copies.

Permission is granted to copy and distribute modified versions of this
manual under the conditions for verbatim copying, provided that the
entire resulting derived work is distributed under the terms of a
permission notice identical to this one.

@end ifinfo

@afourpaper
@paragraphindent none
@finalout

@titlepage
@title tinc Manual
@subtitle Setting up a Virtual Private Network with tinc
@author Ivo Timmermans and Guus Sliepen

@page
@vskip 0pt plus 1filll
This is the info manual for @value{PACKAGE} version @value{VERSION}, a Virtual Private Network daemon.

Copyright @copyright{} 1998-2017 Ivo Timmermans,
Guus Sliepen <guus@@tinc-vpn.org> and
Wessel Dankers <wsl@@tinc-vpn.org>.

Permission is granted to make and distribute verbatim copies of this
manual provided the copyright notice and this permission notice are
preserved on all copies.

Permission is granted to copy and distribute modified versions of this
manual under the conditions for verbatim copying, provided that the
entire resulting derived work is distributed under the terms of a
permission notice identical to this one.

@end titlepage

@ifnottex
@c ==================================================================
@node Top
@top Top

@menu
* Introduction::
* Preparations::
* Installation::
* Configuration::
* Running tinc::
* Controlling tinc::
* Invitations::
* Technical information::
* Platform specific information::
* About us::
* Concept Index::               All used terms explained
@end menu
@end ifnottex

@c ==================================================================
@node    Introduction
@chapter Introduction

@cindex tinc
Tinc is a Virtual Private Network (VPN) daemon that uses tunneling and
encryption to create a secure private network between hosts on the
Internet.

Because the tunnel appears to the IP level network code as a normal
network device, there is no need to adapt any existing software.
The encrypted tunnels allows VPN sites to share information with each other
over the Internet without exposing any information to others.

This document is the manual for tinc.  Included are chapters on how to
configure your computer to use tinc, as well as the configuration
process of tinc itself.

@menu
* Virtual Private Networks::
* tinc::                        About tinc
* Supported platforms::
@end menu

@c ==================================================================
@node    Virtual Private Networks
@section Virtual Private Networks

@cindex VPN
A Virtual Private Network or VPN is a network that can only be accessed
by a few elected computers that participate.  This goal is achievable in
more than just one way.

@cindex private
Private networks can consist of a single stand-alone Ethernet LAN.  Or
even two computers hooked up using a null-modem cable.  In these cases,
it is
obvious that the network is @emph{private}, no one can access it from the
outside.  But if your computers are linked to the Internet, the network
is not private anymore, unless one uses firewalls to block all private
traffic.  But then, there is no way to send private data to trusted
computers on the other end of the Internet.

@cindex virtual
This problem can be solved by using @emph{virtual} networks.  Virtual
networks can live on top of other networks, but they use encapsulation to
keep using their private address space so they do not interfere with
the Internet.  Mostly, virtual networks appear like a single LAN, even though
they can span the entire world.  But virtual networks can't be secured
by using firewalls, because the traffic that flows through it has to go
through the Internet, where other people can look at it.

As is the case with either type of VPN, anybody could eavesdrop.  Or
worse, alter data.  Hence it's probably advisable to encrypt the data
that flows over the network.

When one introduces encryption, we can form a true VPN.  Other people may
see encrypted traffic, but if they don't know how to decipher it (they
need to know the key for that), they cannot read the information that flows
through the VPN.  This is what tinc was made for.


@c ==================================================================
@node    tinc
@section tinc

@cindex vpnd
I really don't quite remember what got us started, but it must have been
Guus' idea.  He wrote a simple implementation (about 50 lines of C) that
used the ethertap device that Linux knows of since somewhere
about kernel 2.1.60.  It didn't work immediately and he improved it a
bit.  At this stage, the project was still simply called "vpnd".

Since then, a lot has changed---to say the least.

@cindex tincd
Tinc now supports encryption, it consists of a single daemon (tincd) for
both the receiving and sending end, it has become largely
runtime-configurable---in short, it has become a full-fledged
professional package.

@cindex traditional VPNs
@cindex scalability
Tinc also allows more than two sites to connect to eachother and form a single VPN.
Traditionally VPNs are created by making tunnels, which only have two endpoints.
Larger VPNs with more sites are created by adding more tunnels.
Tinc takes another approach: only endpoints are specified,
the software itself will take care of creating the tunnels.
This allows for easier configuration and improved scalability.

A lot can---and will be---changed. We have a number of things that we would like to
see in the future releases of tinc.  Not everything will be available in
the near future.  Our first objective is to make tinc work perfectly as
it stands, and then add more advanced features.

Meanwhile, we're always open-minded towards new ideas.  And we're
available too.


@c ==================================================================
@node    Supported platforms
@section Supported platforms

@cindex platforms
Tinc has been verified to work under Linux, FreeBSD, OpenBSD, NetBSD, MacOS/X (Darwin), Solaris, and Windows (both natively and in a Cygwin environment),
with various hardware architectures.  These are some of the platforms
that are supported by the universal tun/tap device driver or other virtual network device drivers.
Without such a driver, tinc will most
likely compile and run, but it will not be able to send or receive data
packets.

@cindex release
For an up to date list of supported platforms, please check the list on
our website:
@uref{https://www.tinc-vpn.org/platforms/}.

@c
@c
@c
@c
@c
@c
@c       Preparing your system
@c
@c
@c
@c
@c

@c ==================================================================
@node    Preparations
@chapter Preparations

This chapter contains information on how to prepare your system to
support tinc.

@menu
* Configuring the kernel::
* Libraries::
@end menu


@c ==================================================================
@node    Configuring the kernel
@section Configuring the kernel

@menu
* Configuration of Linux kernels::
* Configuration of FreeBSD kernels::
* Configuration of OpenBSD kernels::
* Configuration of NetBSD kernels::
* Configuration of Solaris kernels::
* Configuration of Darwin (MacOS/X) kernels::
* Configuration of Windows::
@end menu


@c ==================================================================
@node       Configuration of Linux kernels
@subsection Configuration of Linux kernels

@cindex Universal tun/tap
For tinc to work, you need a kernel that supports the Universal tun/tap device.
Most distributions come with kernels that already support this.
Here are the options you have to turn on when configuring a new kernel:

@example
Code maturity level options
[*] Prompt for development and/or incomplete code/drivers
Network device support
<M> Universal tun/tap device driver support
@end example

It's not necessary to compile this driver as a module, even if you are going to
run more than one instance of tinc.

If you decide to build the tun/tap driver as a kernel module, add these lines
to @file{/etc/modules.conf}:

@example
alias char-major-10-200 tun
@end example


@c ==================================================================
@node       Configuration of FreeBSD kernels
@subsection Configuration of FreeBSD kernels

For FreeBSD version 4.1 and higher, tun and tap drivers are included in the default kernel configuration.
The tap driver can be loaded with @code{kldload if_tap}, or by adding @code{if_tap_load="YES"} to @file{/boot/loader.conf}.


@c ==================================================================
@node       Configuration of OpenBSD kernels
@subsection Configuration of OpenBSD kernels

Recent versions of OpenBSD come with both tun and tap devices enabled in the default kernel configuration.


@c ==================================================================
@node       Configuration of NetBSD kernels
@subsection Configuration of NetBSD kernels

For NetBSD version 1.5.2 and higher,
the tun driver is included in the default kernel configuration.

Tunneling IPv6 may not work on NetBSD's tun device.


@c ==================================================================
@node       Configuration of Solaris kernels
@subsection Configuration of Solaris kernels

For Solaris 8 (SunOS 5.8) and higher,
the tun driver may or may not be included in the default kernel configuration.
If it isn't, the source can be downloaded from @uref{http://vtun.sourceforge.net/tun/}.
For x86 and sparc64 architectures, precompiled versions can be found at @uref{https://www.monkey.org/~dugsong/fragroute/}.
If the @file{net/if_tun.h} header file is missing, install it from the source package.


@c ==================================================================
@node       Configuration of Darwin (MacOS/X) kernels
@subsection Configuration of Darwin (MacOS/X) kernels

Tinc on Darwin relies on a tunnel driver for its data acquisition from the kernel.
OS X version 10.6.8 and later have a built-in tun driver called "utun".
Tinc also supports the driver from @uref{http://tuntaposx.sourceforge.net/},
which supports both tun and tap style devices,

By default, tinc expects the tuntaposx driver to be installed.
To use the utun driver, set add @code{Device = utunX} to @file{tinc.conf},
where X is the desired number for the utun interface.
You can also omit the number, in which case the first free number will be chosen.


@c ==================================================================
@node       Configuration of Windows
@subsection Configuration of Windows

You will need to install the latest TAP-Win32 driver from OpenVPN.
You can download it from @uref{https://openvpn.net/index.php/open-source/downloads.html}.
Using the Network Connections control panel,
configure the TAP-Win32 network interface in the same way as you would do from the tinc-up script,
as explained in the rest of the documentation.


@c ==================================================================
@node    Libraries
@section Libraries

@cindex requirements
@cindex libraries
Before you can configure or build tinc, you need to have the LibreSSL or OpenSSL, zlib,
lzo, curses and readline libraries installed on your system.  If you try to
configure tinc without having them installed, configure will give you an error
message, and stop.

@menu
* LibreSSL/OpenSSL::
* zlib::
* lzo::
* libcurses::
* libreadline::
@end menu


@c ==================================================================
@node       LibreSSL/OpenSSL
@subsection LibreSSL/OpenSSL

@cindex LibreSSL
@cindex OpenSSL
For all cryptography-related functions, tinc uses the functions provided
by the LibreSSL or the OpenSSL library.

If this library is not installed, you wil get an error when configuring
tinc for build.  Support for running tinc with other cryptographic libraries
installed @emph{may} be added in the future.

You can use your operating system's package manager to install this if
available.  Make sure you install the development AND runtime versions
of this package.

If your operating system comes neither with LibreSSL or OpenSSL, you have to
install one manually.  It is recommended that you get the latest version of
LibreSSL from @url{http://www.libressl.org/}.  Instructions on how to
configure, build and install this package are included within the package.
Please make sure you build development and runtime libraries (which is the
default).

If you installed the LibreSSL or OpenSSL libraries from source, it may be necessary
to let configure know where they are, by passing configure one of the
--with-openssl-* parameters. Note that you even have to use --with-openssl-* if you
are using LibreSSL.

@example
--with-openssl=DIR      LibreSSL/OpenSSL library and headers prefix
--with-openssl-include=DIR LibreSSL/OpenSSL headers directory
                        (Default is OPENSSL_DIR/include)
--with-openssl-lib=DIR  LibreSSL/OpenSSL library directory
                        (Default is OPENSSL_DIR/lib)
@end example


@subsubheading License

@cindex license
The complete source code of tinc is covered by the GNU GPL version 2.
Since the license under which OpenSSL is distributed is not directly
compatible with the terms of the GNU GPL
@uref{https://www.openssl.org/support/faq.html#LEGAL2}, we
include an exemption to the GPL (see also the file COPYING.README) to allow
everyone to create a statically or dynamically linked executable:

@quotation
This program is released under the GPL with the additional exemption
that compiling, linking, and/or using OpenSSL is allowed.  You may
provide binary packages linked to the OpenSSL libraries, provided that
all other requirements of the GPL are met.
@end quotation

Since the LZO library used by tinc is also covered by the GPL,
we also present the following exemption:

@quotation
Hereby I grant a special exception to the tinc VPN project
(https://www.tinc-vpn.org/) to link the LZO library with the OpenSSL library
(https://www.openssl.org).

Markus F.X.J. Oberhumer
@end quotation


@c ==================================================================
@node       zlib
@subsection zlib

@cindex zlib
For the optional compression of UDP packets, tinc uses the functions provided
by the zlib library.

If this library is not installed, you wil get an error when running the
configure script.  You can either install the zlib library, or disable support
for zlib compression by using the "--disable-zlib" option when running the
configure script. Note that if you disable support for zlib, the resulting
binary will not work correctly on VPNs where zlib compression is used.

You can use your operating system's package manager to install this if
available.  Make sure you install the development AND runtime versions
of this package.

If you have to install zlib manually, you can get the source code
from @url{http://www.zlib.net/}.  Instructions on how to configure,
build and install this package are included within the package.  Please
make sure you build development and runtime libraries (which is the
default).


@c ==================================================================
@node       lzo
@subsection lzo

@cindex lzo
Another form of compression is offered using the LZO library.

If this library is not installed, you wil get an error when running the
configure script.  You can either install the LZO library, or disable support
for LZO compression by using the "--disable-lzo" option when running the
configure script. Note that if you disable support for LZO, the resulting
binary will not work correctly on VPNs where LZO compression is used.

You can use your operating system's package manager to install this if
available.  Make sure you install the development AND runtime versions
of this package.

If you have to install lzo manually, you can get the source code
from @url{https://www.oberhumer.com/opensource/lzo/}.  Instructions on how to configure,
build and install this package are included within the package.  Please
make sure you build development and runtime libraries (which is the
default).


@c ==================================================================
@node       libcurses
@subsection libcurses

@cindex libcurses
For the "tinc top" command, tinc requires a curses library.

If this library is not installed, you wil get an error when running the
configure script.  You can either install a suitable curses library, or disable
all functionality that depends on a curses library by using the
"--disable-curses" option when running the configure script.

There are several curses libraries. It is recommended that you install
"ncurses" (@url{http://invisible-island.net/ncurses/}),
however other curses libraries should also work.
In particular, "PDCurses" (@url{http://pdcurses.sourceforge.net/})
is recommended if you want to compile tinc for Windows.

You can use your operating system's package manager to install this if
available. Make sure you install the development AND runtime versions
of this package.


@c ==================================================================
@node       libreadline
@subsection libreadline

@cindex libreadline
For the "tinc" command's shell functionality, tinc uses the readline library.

If this library is not installed, you wil get an error when running the
configure script.  You can either install a suitable readline library, or
disable all functionality that depends on a readline library by using the
"--disable-readline" option when running the configure script.

You can use your operating system's package manager to install this if
available.  Make sure you install the development AND runtime versions
of this package.

If you have to install libreadline manually, you can get the source code from
@url{http://www.gnu.org/software/readline/}. Instructions on how to configure,
build and install this package are included within the package.  Please make
sure you build development and runtime libraries (which is the default).


@c
@c
@c
@c      Installing tinc
@c
@c
@c
@c

@c ==================================================================
@node    Installation
@chapter Installation

If you use Debian, you may want to install one of the
precompiled packages for your system.  These packages are equipped with
system startup scripts and sample configurations.

If you cannot use one of the precompiled packages, or you want to compile tinc
for yourself, you can use the source.  The source is distributed under
the GNU General Public License (GPL).  Download the source from the
@uref{https://www.tinc-vpn.org/download/, download page}.

Tinc comes in a convenient autoconf/automake package, which you can just
treat the same as any other package.  Which is just untar it, type
`./configure' and then `make'.
More detailed instructions are in the file @file{INSTALL}, which is
included in the source distribution.

@menu
* Building and installing tinc::
* System files::
@end menu


@c ==================================================================
@node    Building and installing tinc
@section Building and installing tinc

Detailed instructions on configuring the source, building tinc and installing tinc
can be found in the file called @file{INSTALL}.

@cindex binary package
If you happen to have a binary package for tinc for your distribution,
you can use the package management tools of that distribution to install tinc.
The documentation that comes along with your distribution will tell you how to do that.

@menu
* Darwin (MacOS/X) build environment::
* Cygwin (Windows) build environment::
* MinGW (Windows) build environment::
@end menu


@c ==================================================================
@node       Darwin (MacOS/X) build environment
@subsection Darwin (MacOS/X) build environment

In order to build tinc on Darwin, you need to install Xcode from @uref{https://developer.apple.com/xcode/}.
It might also help to install a recent version of Fink from @uref{http://www.finkproject.org/}.

You need to download and install LibreSSL (or OpenSSL) and LZO,
either directly from their websites (see @ref{Libraries}) or using Fink.

@c ==================================================================
@node       Cygwin (Windows) build environment
@subsection Cygwin (Windows) build environment

If Cygwin hasn't already been installed, install it directly from
@uref{https://www.cygwin.com/}.

When tinc is compiled in a Cygwin environment, it can only be run in this environment,
but all programs, including those started outside the Cygwin environment, will be able to use the VPN.
It will also support all features.

@c ==================================================================
@node       MinGW (Windows) build environment
@subsection MinGW (Windows) build environment

You will need to install the MinGW environment from @uref{http://www.mingw.org}.
You also need to download and install LibreSSL (or OpenSSL) and LZO.

When tinc is compiled using MinGW it runs natively under Windows,
it is not necessary to keep MinGW installed.

When detaching, tinc will install itself as a service,
which will be restarted automatically after reboots.


@c ==================================================================
@node    System files
@section System files

Before you can run tinc, you must make sure you have all the needed
files on your system.

@menu
* Device files::
* Other files::
@end menu


@c ==================================================================
@node       Device files
@subsection Device files

@cindex device files
Most operating systems nowadays come with the necessary device files by default,
or they have a mechanism to create them on demand.

If you use Linux and do not have udev installed,
you may need to create the following device file if it does not exist:

@example
mknod -m 600 /dev/net/tun c 10 200
@end example


@c ==================================================================
@node       Other files
@subsection Other files

@subsubheading @file{/etc/networks}

You may add a line to @file{/etc/networks} so that your VPN will get a
symbolic name.  For example:

@example
myvpn 10.0.0.0
@end example

@subsubheading @file{/etc/services}

@cindex port numbers
You may add this line to @file{/etc/services}.  The effect is that you
may supply a @samp{tinc} as a valid port number to some programs.  The
number 655 is registered with the IANA.

@example
tinc            655/tcp    TINC
tinc            655/udp    TINC
#                          Ivo Timmermans <ivo@@tinc-vpn.org>
@end example


@c
@c
@c
@c
@c         Configuring tinc
@c
@c
@c
@c


@c ==================================================================
@node    Configuration
@chapter Configuration

@menu
* Configuration introduction::
* Multiple networks::
* How connections work::
* Configuration files::
* Network interfaces::
* Example configuration::
@end menu

@c ==================================================================
@node    Configuration introduction
@section Configuration introduction

Before actually starting to configure tinc and editing files,
make sure you have read this entire section so you know what to expect.
Then, make it clear to yourself how you want to organize your VPN:
What are the nodes (computers running tinc)?
What IP addresses/subnets do they have?
What is the network mask of the entire VPN?
Do you need special firewall rules?
Do you have to set up masquerading or forwarding rules?
Do you want to run tinc in router mode or switch mode?
These questions can only be answered by yourself,
you will not find the answers in this documentation.
Make sure you have an adequate understanding of networks in general.
@cindex Network Administrators Guide
A good resource on networking is the
@uref{http://www.tldp.org/LDP/nag2/, Linux Network Administrators Guide}.

If you have everything clearly pictured in your mind,
proceed in the following order:
First, create the initial configuration files and public/private keypairs using the following command:
@example
tinc -n @var{NETNAME} init @var{NAME}
@end example
Second, use @samp{tinc -n @var{NETNAME} add ...} to further configure tinc.
Finally, export your host configuration file using @samp{tinc -n @var{NETNAME} export} and send it to those
people or computers you want tinc to connect to.
They should send you their host configuration file back, which you can import using @samp{tinc -n @var{NETNAME} import}.

These steps are described in the subsections below.


@c ==================================================================
@node    Multiple networks
@section Multiple networks

@cindex multiple networks
@cindex netname

In order to allow you to run more than one tinc daemon on one computer,
for instance if your computer is part of more than one VPN,
you can assign a @var{netname} to your VPN.
It is not required if you only run one tinc daemon,
it doesn't even have to be the same on all the nodes of your VPN,
but it is recommended that you choose one anyway.

We will asume you use a netname throughout this document.
This means that you call tinc with the -n argument,
which will specify the netname.

The effect of this option is that tinc will set its configuration
root to @file{@value{sysconfdir}/tinc/@var{netname}/}, where @var{netname} is your argument to the -n option.
You will also notice that log messages it appears in syslog as coming from @file{tinc.@var{netname}},
and on Linux, unless specified otherwise, the name of the virtual network interface will be the same as the network name.

However, it is not strictly necessary that you call tinc with the -n
option. If you do not use it, the network name will just be empty, and
tinc will look for files in @file{@value{sysconfdir}/tinc/} instead of
@file{@value{sysconfdir}/tinc/@var{netname}/};
the configuration file will then be @file{@value{sysconfdir}/tinc/tinc.conf},
and the host configuration files are expected to be in @file{@value{sysconfdir}/tinc/hosts/}.


@c ==================================================================
@node    How connections work
@section How connections work

When tinc starts up, it parses the command-line options and then
reads in the configuration file tinc.conf.
If it sees one or more  `ConnectTo' values pointing to other tinc daemons in that file,
it will try to connect to those other daemons.
Whether this succeeds or not and whether `ConnectTo' is specified or not,
tinc will listen for incoming connection from other deamons.
If you did specify a `ConnectTo' value and the other side is not responding,
tinc will keep retrying.
This means that once started, tinc will stay running until you tell it to stop,
and failures to connect to other tinc daemons will not stop your tinc daemon
for trying again later.
This means you don't have to intervene if there are temporary network problems.

@cindex client
@cindex server
There is no real distinction between a server and a client in tinc.
If you wish, you can view a tinc daemon without a `ConnectTo' value as a server,
and one which does specify such a value as a client.
It does not matter if two tinc daemons have a `ConnectTo' value pointing to each other however.

Connections specified using `ConnectTo' are so-called meta-connections.
Tinc daemons exchange information about all other daemon they know about via these meta-connections.
After learning about all the daemons in the VPN,
tinc will create other connections as necessary in order to communicate with them.
For example, if there are three daemons named A, B and C, and A has @samp{ConnectTo = B} in its tinc.conf file,
and C has @samp{ConnectTo = B} in its tinc.conf file, then A will learn about C from B,
and will be able to exchange VPN packets with C without the need to have @samp{ConnectTo = C} in its tinc.conf file.

It could be that some daemons are located behind a Network Address Translation (NAT) device, or behind a firewall.
In the above scenario with three daemons, if A and C are behind a NAT,
B will automatically help A and C punch holes through their NAT,
in a way similar to the STUN protocol, so that A and C can still communicate with each other directly.
It is not always possible to do this however, and firewalls might also prevent direct communication.
In that case, VPN packets between A and C will be forwarded by B.

In effect, all nodes in the VPN will be able to talk to each other, as long as
their is a path of meta-connections between them, and whenever possible, two
nodes will communicate with each other directly.


@c ==================================================================
@node    Configuration files
@section Configuration files

The actual configuration of the daemon is done in the file
@file{@value{sysconfdir}/tinc/@var{netname}/tinc.conf} and at least one other file in the directory
@file{@value{sysconfdir}/tinc/@var{netname}/hosts/}.

An optionnal directory @file{@value{sysconfdir}/tinc/@var{netname}/conf.d} can be added from which
any .conf file will be read.

These file consists of comments (lines started with a #) or assignments
in the form of

@example
Variable = Value.
@end example

The variable names are case insensitive, and any spaces, tabs, newlines
and carriage returns are ignored.  Note: it is not required that you put
in the `=' sign, but doing so improves readability.  If you leave it
out, remember to replace it with at least one space character.

The server configuration is complemented with host specific configuration (see
the next section). Although all host configuration options for the local node
listed in this document can also be put in
@file{@value{sysconfdir}/tinc/@var{netname}/tinc.conf}, it is recommended to
put host specific configuration options in the host configuration file, as this
makes it easy to exchange with other nodes.

You can edit the config file manually, but it is recommended that you use
the tinc command to change configuration variables for you.

In the following two subsections all valid variables are listed in alphabetical order.
The default value is given between parentheses,
other comments are between square brackets.

@menu
* Main configuration variables::
* Host configuration variables::
* Scripts::
* How to configure::
@end menu


@c ==================================================================
@node       Main configuration variables
@subsection Main configuration variables

@table @asis
@cindex AddressFamily
@item AddressFamily = <ipv4|ipv6|any> (any)
This option affects the address family of listening and outgoing sockets.
If any is selected, then depending on the operating system
both IPv4 and IPv6 or just IPv6 listening sockets will be created.

@cindex AutoConnect
@item AutoConnect = <yes|no> (no) [experimental]
If set to yes, tinc will automatically set up meta connections to other nodes,
without requiring @var{ConnectTo} variables.

@cindex BindToAddress
@item BindToAddress = <@var{address}> [<@var{port}>]
This is the same as ListenAddress, however the address given with the BindToAddress option
will also be used for outgoing connections.
This is useful if your computer has more than one IPv4 or IPv6 address,
and you want tinc to only use a specific one for outgoing packets.

@cindex BindToInterface
@item BindToInterface = <@var{interface}> [experimental]
If you have more than one network interface in your computer, tinc will
by default listen on all of them for incoming connections.  It is
possible to bind tinc to a single interface like eth0 or ppp0 with this
variable.

This option may not work on all platforms.
Also, on some platforms it will not actually bind to an interface,
but rather to the address that the interface has at the moment a socket is created.

@cindex Broadcast
@item Broadcast = <no | mst | direct> (mst) [experimental]
This option selects the way broadcast packets are sent to other daemons.
@emph{NOTE: all nodes in a VPN must use the same Broadcast mode, otherwise routing loops can form.}

@table @asis
@item no
Broadcast packets are never sent to other nodes.

@item mst
Broadcast packets are sent and forwarded via the VPN's Minimum Spanning Tree.
This ensures broadcast packets reach all nodes.

@item direct
Broadcast packets are sent directly to all nodes that can be reached directly.
Broadcast packets received from other nodes are never forwarded.
If the IndirectData option is also set, broadcast packets will only be sent to nodes which we have a meta connection to.
@end table

@cindex BroadcastSubnet
@item BroadcastSubnet = @var{address}[/@var{prefixlength}]
Declares a broadcast subnet.
Any packet with a destination address falling into such a subnet will be routed as a broadcast
(provided all nodes have it declared).
This is most useful to declare subnet broadcast addresses (e.g. 10.42.255.255),
otherwise tinc won't know what to do with them.

Note that global broadcast addresses (MAC ff:ff:ff:ff:ff:ff, IPv4 255.255.255.255),
as well as multicast space (IPv4 224.0.0.0/4, IPv6 ff00::/8)
are always considered broadcast addresses and don't need to be declared.

@cindex ConnectTo
@item ConnectTo = <@var{name}>
Specifies which other tinc daemon to connect to on startup.
Multiple ConnectTo variables may be specified,
in which case outgoing connections to each specified tinc daemon are made.
The names should be known to this tinc daemon
(i.e., there should be a host configuration file for the name on the ConnectTo line).

If you don't specify a host with ConnectTo and don't enable AutoConnect,
tinc won't try to connect to other daemons at all,
and will instead just listen for incoming connections.

@cindex DecrementTTL
@item DecrementTTL = <yes | no> (no) [experimental]
When enabled, tinc will decrement the Time To Live field in IPv4 packets, or the Hop Limit field in IPv6 packets,
before forwarding a received packet to the virtual network device or to another node,
and will drop packets that have a TTL value of zero,
in which case it will send an ICMP Time Exceeded packet back.

Do not use this option if you use switch mode and want to use IPv6.

@cindex Device
@item Device = <@var{device}> (@file{/dev/tap0}, @file{/dev/net/tun} or other depending on platform)
The virtual network device to use.
Tinc will automatically detect what kind of device it is.
Note that you can only use one device per daemon.
Under Windows, use @var{Interface} instead of @var{Device}.
Note that you can only use one device per daemon.
See also @ref{Device files}.

@cindex DeviceStandby
@item DeviceStandby = <yes | no> (no)
When disabled, tinc calls @file{tinc-up} on startup, and @file{tinc-down} on shutdown.
When enabled, tinc will only call @file{tinc-up} when at least one node is reachable,
and will call @file{tinc-down} as soon as no nodes are reachable.
On Windows, this also determines when the virtual network interface "cable" is "plugged".

@cindex DeviceType
@item DeviceType = <@var{type}> (platform dependent)
The type of the virtual network device.
Tinc will normally automatically select the right type of tun/tap interface, and this option should not be used.
However, this option can be used to select one of the special interface types, if support for them is compiled in.

@table @asis
@cindex dummy
@item dummy
Use a dummy interface.
No packets are ever read or written to a virtual network device.
Useful for testing, or when setting up a node that only forwards packets for other nodes.

@cindex raw_socket
@item raw_socket
Open a raw socket, and bind it to a pre-existing
@var{Interface} (eth0 by default).
All packets are read from this interface.
Packets received for the local node are written to the raw socket.
However, at least on Linux, the operating system does not process IP packets destined for the local host.

@cindex multicast
@item multicast
Open a multicast UDP socket and bind it to the address and port (separated by spaces) and optionally a TTL value specified using @var{Device}.
Packets are read from and written to this multicast socket.
This can be used to connect to UML, QEMU or KVM instances listening on the same multicast address.
Do NOT connect multiple tinc daemons to the same multicast address, this will very likely cause routing loops.
Also note that this can cause decrypted VPN packets to be sent out on a real network if misconfigured.

@cindex fd
@item fd
Use a file descriptor.
All packets are read from this interface.
Packets received for the local node are written to it.

@cindex UML
@item uml (not compiled in by default)
Create a UNIX socket with the filename specified by
@var{Device}, or @file{@value{localstatedir}/run/@var{netname}.umlsocket}
if not specified.
Tinc will wait for a User Mode Linux instance to connect to this socket.

@cindex VDE
@item vde (not compiled in by default)
Uses the libvdeplug library to connect to a Virtual Distributed Ethernet switch,
using the UNIX socket specified by
@var{Device}, or @file{@value{localstatedir}/run/vde.ctl}
if not specified.
@end table

Also, in case tinc does not seem to correctly interpret packets received from the virtual network device,
it can be used to change the way packets are interpreted:

@table @asis
@item tun (BSD and Linux)
Set type to tun.
Depending on the platform, this can either be with or without an address family header (see below).

@cindex tunnohead
@item tunnohead (BSD)
Set type to tun without an address family header.
Tinc will expect packets read from the virtual network device to start with an IP header.
On some platforms IPv6 packets cannot be read from or written to the device in this mode.

@cindex tunifhead
@item tunifhead (BSD)
Set type to tun with an address family header.
Tinc will expect packets read from the virtual network device
to start with a four byte header containing the address family,
followed by an IP header.
This mode should support both IPv4 and IPv6 packets.

@cindex utun
@item utun (OS X)
Set type to utun.
This is only supported on OS X version 10.6.8 and higher, but doesn't require the tuntaposx module.
This mode should support both IPv4 and IPv6 packets.

@item tap (BSD and Linux)
Set type to tap.
Tinc will expect packets read from the virtual network device
to start with an Ethernet header.
@end table

@cindex DirectOnly
@item DirectOnly = <yes|no> (no) [experimental]
When this option is enabled, packets that cannot be sent directly to the destination node,
but which would have to be forwarded by an intermediate node, are dropped instead.
When combined with the IndirectData option,
packets for nodes for which we do not have a meta connection with are also dropped.

@cindex Ed25519PrivateKeyFile
@item Ed25519PrivateKeyFile = <@var{path}> (@file{@value{sysconfdir}/tinc/@var{netname}/ed25519_key.priv})
The file in which the private Ed25519 key of this tinc daemon resides.
This is only used if ExperimentalProtocol is enabled.

@cindex ExperimentalProtocol
@item ExperimentalProtocol = <yes|no> (yes)
When this option is enabled, the SPTPS protocol will be used when connecting to nodes that also support it.
Ephemeral ECDH will be used for key exchanges,
and Ed25519 will be used instead of RSA for authentication.
When enabled, an Ed25519 key must have been generated before with
@samp{tinc generate-ed25519-keys}.

@cindex Forwarding
@item Forwarding = <off|internal|kernel> (internal) [experimental]
This option selects the way indirect packets are forwarded.

@table @asis
@item off
Incoming packets that are not meant for the local node,
but which should be forwarded to another node, are dropped.

@item internal
Incoming packets that are meant for another node are forwarded by tinc internally.

This is the default mode, and unless you really know you need another forwarding mode, don't change it.

@item kernel
Incoming packets are always sent to the TUN/TAP device, even if the packets are not for the local node.
This is less efficient, but allows the kernel to apply its routing and firewall rules on them,
and can also help debugging.
@end table

@cindex Hostnames
@item Hostnames = <yes|no> (no)
This option selects whether IP addresses (both real and on the VPN)
should be resolved.  Since DNS lookups are blocking, it might affect
tinc's efficiency, even stopping the daemon for a few seconds everytime
it does a lookup if your DNS server is not responding.

This does not affect resolving hostnames to IP addresses from the
configuration file, but whether hostnames should be resolved while logging.

@cindex Interface
@item Interface = <@var{interface}>
Defines the name of the interface corresponding to the virtual network device.
Depending on the operating system and the type of device this may or may not actually set the name of the interface.
Under Windows, this variable is used to select which network interface will be used.
If you specified a Device, this variable is almost always already correctly set.

@cindex ListenAddress
@item ListenAddress = <@var{address}> [<@var{port}>]
If your computer has more than one IPv4 or IPv6 address, tinc
will by default listen on all of them for incoming connections.
This option can be used to restrict which addresses tinc listens on.
Multiple ListenAddress variables may be specified,
in which case listening sockets for each specified address are made.

If no @var{port} is specified, the socket will listen on the port specified by the Port option,
or to port 655 if neither is given.
To only listen on a specific port but not to a specific address, use "*" for the @var{address}.

@cindex LocalDiscovery
@item LocalDiscovery = <yes | no> (no)
When enabled, tinc will try to detect peers that are on the same local network.
This will allow direct communication using LAN addresses, even if both peers are behind a NAT
and they only ConnectTo a third node outside the NAT,
which normally would prevent the peers from learning each other's LAN address.

Currently, local discovery is implemented by sending some packets to the local address of the node during UDP discovery.
This will not work with old nodes that don't transmit their local address.

@cindex LogLevel
@item LogLevel = <@var{level}> (0)
This option controls the verbosity of the logging.
See @ref{Debug levels}.

@cindex Mode
@item Mode = <router|switch|hub> (router)
This option selects the way packets are routed to other daemons.

@table @asis
@cindex router
@item router
In this mode Subnet
variables in the host configuration files will be used to form a routing table.
Only packets of routable protocols (IPv4 and IPv6) are supported in this mode.

This is the default mode, and unless you really know you need another mode, don't change it.

@cindex switch
@item switch
In this mode the MAC addresses of the packets on the VPN will be used to
dynamically create a routing table just like an Ethernet switch does.
Unicast, multicast and broadcast packets of every protocol that runs over Ethernet are supported in this mode
at the cost of frequent broadcast ARP requests and routing table updates.

This mode is primarily useful if you want to bridge Ethernet segments.

@cindex hub
@item hub
This mode is almost the same as the switch mode, but instead
every packet will be broadcast to the other daemons
while no routing table is managed.
@end table

@cindex InvitationExpire
@item InvitationExpire = <@var{seconds}> (604800)
This option controls the time invitations are valid.

@cindex KeyExpire
@item KeyExpire = <@var{seconds}> (3600)
This option controls the time the encryption keys used to encrypt the data
are valid.  It is common practice to change keys at regular intervals to
make it even harder for crackers, even though it is thought to be nearly
impossible to crack a single key.

@cindex MACExpire
@item MACExpire = <@var{seconds}> (600)
This option controls the amount of time MAC addresses are kept before they are removed.
This only has effect when Mode is set to "switch".

@cindex MaxConnectionBurst
@item MaxConnectionBurst = <@var{count}> (100)
This option controls how many connections tinc accepts in quick succession.
If there are more connections than the given number in a short time interval,
tinc will reduce the number of accepted connections to only one per second,
until the burst has passed.

@cindex Name
@item Name = <@var{name}> [required]
This is a symbolic name for this connection.
The name must consist only of alfanumeric and underscore characters (a-z, A-Z, 0-9 and _), and is case sensitive.

If Name starts with a $, then the contents of the environment variable that follows will be used.
In that case, invalid characters will be converted to underscores.
If Name is $HOST, but no such environment variable exist,
the hostname will be read using the gethostname() system call.

@cindex PingInterval
@item PingInterval = <@var{seconds}> (60)
The number of seconds of inactivity that tinc will wait before sending a
probe to the other end.

@cindex PingTimeout
@item PingTimeout = <@var{seconds}> (5)
The number of seconds to wait for a response to pings or to allow meta
connections to block. If the other end doesn't respond within this time,
the connection is terminated, and the others will be notified of this.

@cindex PriorityInheritance
@item PriorityInheritance = <yes|no> (no) [experimental]
When this option is enabled the value of the TOS field of tunneled IPv4 packets
will be inherited by the UDP packets that are sent out.

@cindex PrivateKey
@item PrivateKey = <@var{key}> [obsolete]
This is the RSA private key for tinc. However, for safety reasons it is
advised to store private keys of any kind in separate files. This prevents
accidental eavesdropping if you are editting the configuration file.

@cindex PrivateKeyFile
@item PrivateKeyFile = <@var{path}> (@file{@value{sysconfdir}/tinc/@var{netname}/rsa_key.priv})
This is the full path name of the RSA private key file that was
generated by @samp{tinc generate-keys}.  It must be a full path, not a
relative directory.

@cindex ProcessPriority
@item ProcessPriority = <low|normal|high>
When this option is used the priority of the tincd process will be adjusted.
Increasing the priority may help to reduce latency and packet loss on the VPN.

@cindex Proxy
@item Proxy = socks4 | socks5 | http | exec @var{...} [experimental]
Use a proxy when making outgoing connections.
The following proxy types are currently supported:

@table @asis
@cindex socks4
@item socks4 <@var{address}> <@var{port}> [<@var{username}>]
Connects to the proxy using the SOCKS version 4 protocol.
Optionally, a @var{username} can be supplied which will be passed on to the proxy server.

@cindex socks5
@item socks5 <@var{address}> <@var{port}> [<@var{username}> <@var{password}>]
Connect to the proxy using the SOCKS version 5 protocol.
If a @var{username} and @var{password} are given, basic username/password authentication will be used,
otherwise no authentication will be used.

@cindex http
@item http <@var{address}> <@var{port}>
Connects to the proxy and sends a HTTP CONNECT request.

@cindex exec
@item exec <@var{command}>
Executes the given command which should set up the outgoing connection.
The environment variables @env{NAME}, @env{NODE}, @env{REMOTEADDRES} and @env{REMOTEPORT} are available.
@end table

@cindex ReplayWindow
@item ReplayWindow = <bytes> (32)
This is the size of the replay tracking window for each remote node, in bytes.
The window is a bitfield which tracks 1 packet per bit, so for example
the default setting of 32 will track up to 256 packets in the window. In high
bandwidth scenarios, setting this to a higher value can reduce packet loss from
the interaction of replay tracking with underlying real packet loss and/or
reordering. Setting this to zero will disable replay tracking completely and
pass all traffic, but leaves tinc vulnerable to replay-based attacks on your
traffic.

@cindex StrictSubnets
@item StrictSubnets = <yes|no> (no) [experimental]
When this option is enabled tinc will only use Subnet statements which are
present in the host config files in the local
@file{@value{sysconfdir}/tinc/@var{netname}/hosts/} directory.
Subnets learned via connections to other nodes and which are not
present in the local host config files are ignored.

@cindex TunnelServer
@item TunnelServer = <yes|no> (no) [experimental]
When this option is enabled tinc will no longer forward information between other tinc daemons,
and will only allow connections with nodes for which host config files are present in the local
@file{@value{sysconfdir}/tinc/@var{netname}/hosts/} directory.
Setting this options also implicitly sets StrictSubnets.

@cindex UDPDiscovey
@item UDPDiscovery = <yes|no> (yes)
When this option is enabled tinc will try to establish UDP connectivity to nodes,
using TCP while it determines if a node is reachable over UDP. If it is disabled,
tinc always assumes a node is reachable over UDP.
Note that tinc will never use UDP with nodes that have TCPOnly enabled.

@cindex UDPDiscoveryKeepaliveInterval
@item UDPDiscoveryKeepaliveInterval = <seconds> (9)
The minimum amount of time between sending UDP ping datagrams to check UDP connectivity once it has been established.
Note that these pings are large, since they are used to verify link MTU as well.

@cindex UDPDiscoveryInterval
@item UDPDiscoveryInterval = <seconds> (2)
The minimum amount of time between sending UDP ping datagrams to try to establish UDP connectivity.

@cindex UDPDiscoveryTimeout
@item UDPDiscoveryTimeout = <seconds> (30)
If tinc doesn't receive any UDP ping replies over the specified interval,
it will assume UDP communication is broken and will fall back to TCP.

@cindex UDPInfoInterval
@item UDPInfoInterval = <seconds> (5)
The minimum amount of time between sending periodic updates about UDP addresses, which are mostly useful for UDP hole punching.

@cindex UDPRcvBuf
@item UDPRcvBuf = <bytes> (1048576)
Sets the socket receive buffer size for the UDP socket, in bytes.
If set to zero, the default buffer size will be used by the operating system.
Note: this setting can have a significant impact on performance, especially raw throughput.

@cindex UDPSndBuf
@item UDPSndBuf = <bytes> (1048576)
Sets the socket send buffer size for the UDP socket, in bytes.
If set to zero, the default buffer size will be used by the operating system.
Note: this setting can have a significant impact on performance, especially raw throughput.

@cindex UPnP
@item UPnP = <yes|udponly|no> (no)
If this option is enabled then tinc will search for UPnP-IGD devices on the local network.
It will then create and maintain port mappings for tinc's listening TCP and UDP ports.
If set to "udponly", tinc will only create a mapping for its UDP (data) port, not for its TCP (metaconnection) port.
Note that tinc must have been built with miniupnpc support for this feature to be available.
Furthermore, be advised that enabling this can have security implications, because the miniupnpc library that
tinc uses might not be well-hardened with regard to malicious UPnP replies.

@cindex UPnPDiscoverWait
@item UPnPDiscoverWait = <seconds> (5)
The amount of time to wait for replies when probing the local network for UPnP devices.

@cindex UPnPRefreshPeriod
@item UPnPRefreshPeriod = <seconds> (5)
How often tinc will re-add the port mapping, in case it gets reset on the UPnP device.
This also controls the duration of the port mapping itself, which will be set to twice that duration.

@end table


@c ==================================================================
@node       Host configuration variables
@subsection Host configuration variables

@table @asis
@cindex Address
@item Address = <@var{IP address}|@var{hostname}> [<port>] [recommended]
This variable is only required if you want to connect to this host.  It
must resolve to the external IP address where the host can be reached,
not the one that is internal to the VPN.
If no port is specified, the default Port is used.
Multiple Address variables can be specified, in which case each address will be
tried until a working connection has been established.

@cindex Cipher
@item Cipher = <@var{cipher}> (blowfish)
The symmetric cipher algorithm used to encrypt UDP packets using the legacy protocol.
Any cipher supported by LibreSSL or OpenSSL is recognized.
Furthermore, specifying "none" will turn off packet encryption.
It is best to use only those ciphers which support CBC mode.
This option has no effect for connections using the SPTPS protocol, which always use AES-256-CTR.

@cindex ClampMSS
@item ClampMSS = <yes|no> (yes)
This option specifies whether tinc should clamp the maximum segment size (MSS)
of TCP packets to the path MTU. This helps in situations where ICMP
Fragmentation Needed or Packet too Big messages are dropped by firewalls.

@cindex Compression
@item Compression = <@var{level}> (0)
This option sets the level of compression used for UDP packets.
Possible values are 0 (off), 1 (fast zlib) and any integer up to 9 (best zlib),
10 (fast lzo) and 11 (best lzo).

@cindex Digest
@item Digest = <@var{digest}> (sha1)
The digest algorithm used to authenticate UDP packets using the legacy protocol.
Any digest supported by LibreSSL or OpenSSL is recognized.
Furthermore, specifying "none" will turn off packet authentication.
This option has no effect for connections using the SPTPS protocol, which always use HMAC-SHA-256.

@cindex IndirectData
@item IndirectData = <yes|no> (no)
When set to yes, other nodes which do not already have a meta connection to you
will not try to establish direct communication with you.
It is best to leave this option out or set it to no.

@cindex MACLength
@item MACLength = <@var{bytes}> (4)
The length of the message authentication code used to authenticate UDP packets using the legacy protocol.
Can be anything from 0
up to the length of the digest produced by the digest algorithm.
This option has no effect for connections using the SPTPS protocol, which never truncate MACs.

@cindex PMTU
@item PMTU = <@var{mtu}> (1514)
This option controls the initial path MTU to this node.

@cindex PMTUDiscovery
@item PMTUDiscovery = <yes|no> (yes)
When this option is enabled, tinc will try to discover the path MTU to this node.
After the path MTU has been discovered, it will be enforced on the VPN.

@cindex MTUInfoInterval
@item MTUInfoInterval = <seconds> (5)
The minimum amount of time between sending periodic updates about relay path MTU. Useful for quickly determining MTU to indirect nodes.

@cindex Port
@item Port = <@var{port}> (655)
This is the port this tinc daemon listens on.
You can use decimal portnumbers or symbolic names (as listed in @file{/etc/services}).

@cindex PublicKey
@item PublicKey = <@var{key}> [obsolete]
This is the RSA public key for this host.

@cindex PublicKeyFile
@item PublicKeyFile = <@var{path}> [obsolete]
This is the full path name of the RSA public key file that was generated
by @samp{tinc generate-keys}.  It must be a full path, not a relative
directory.

@cindex PEM format
From version 1.0pre4 on tinc will store the public key directly into the
host configuration file in PEM format, the above two options then are not
necessary. Either the PEM format is used, or exactly
@strong{one of the above two options} must be specified
in each host configuration file, if you want to be able to establish a
connection with that host.

@cindex Subnet
@item Subnet = <@var{address}[/@var{prefixlength}[#@var{weight}]]>
The subnet which this tinc daemon will serve.
Tinc tries to look up which other daemon it should send a packet to by searching the appropiate subnet.
If the packet matches a subnet,
it will be sent to the daemon who has this subnet in his host configuration file.
Multiple subnet lines can be specified for each daemon.

Subnets can either be single MAC, IPv4 or IPv6 addresses,
in which case a subnet consisting of only that single address is assumed,
or they can be a IPv4 or IPv6 network address with a prefixlength.
For example, IPv4 subnets must be in a form like 192.168.1.0/24,
where 192.168.1.0 is the network address and 24 is the number of bits set in the netmask.
Note that subnets like 192.168.1.1/24 are invalid!
Read a networking HOWTO/FAQ/guide if you don't understand this.
IPv6 subnets are notated like fec0:0:0:1::/64.
MAC addresses are notated like 0:1a:2b:3c:4d:5e.

@cindex CIDR notation
Prefixlength is the number of bits set to 1 in the netmask part; for
example: netmask 255.255.255.0 would become /24, 255.255.252.0 becomes
/22. This conforms to standard CIDR notation as described in
@uref{https://www.ietf.org/rfc/rfc1519.txt, RFC1519}

A Subnet can be given a weight to indicate its priority over identical Subnets
owned by different nodes. The default weight is 10. Lower values indicate
higher priority. Packets will be sent to the node with the highest priority,
unless that node is not reachable, in which case the node with the next highest
priority will be tried, and so on.

@cindex TCPonly
@item TCPonly = <yes|no> (no)
If this variable is set to yes, then the packets are tunnelled over a
TCP connection instead of a UDP connection.  This is especially useful
for those who want to run a tinc daemon from behind a masquerading
firewall, or if UDP packet routing is disabled somehow.
Setting this options also implicitly sets IndirectData.

@cindex Weight
@item Weight = <weight>
If this variable is set, it overrides the weight given to connections made with
another host. A higher weight means a lower priority is given to this
connection when broadcasting or forwarding packets.
@end table


@c ==================================================================
@node       Scripts
@subsection Scripts

@cindex scripts
Apart from reading the server and host configuration files,
tinc can also run scripts at certain moments.
Below is a list of filenames of scripts and a description of when they are run.
A script is only run if it exists and if it is executable.

Scripts are run synchronously;
this means that tinc will temporarily stop processing packets until the called script finishes executing.
This guarantees that scripts will execute in the exact same order as the events that trigger them.
If you need to run commands asynchronously, you have to ensure yourself that they are being run in the background.

Under Windows (not Cygwin), the scripts should have the extension @file{.bat} or @file{.cmd}.

@table @file
@cindex tinc-up
@item @value{sysconfdir}/tinc/@var{netname}/tinc-up
This is the most important script.
If it is present it will be executed right after the tinc daemon has been
started and has connected to the virtual network device.
It should be used to set up the corresponding network interface,
but can also be used to start other things.

Under Windows you can use the Network Connections control panel instead of creating this script.

@cindex tinc-down
@item @value{sysconfdir}/tinc/@var{netname}/tinc-down
This script is started right before the tinc daemon quits.

@item @value{sysconfdir}/tinc/@var{netname}/hosts/@var{host}-up
This script is started when the tinc daemon with name @var{host} becomes reachable.

@item @value{sysconfdir}/tinc/@var{netname}/hosts/@var{host}-down
This script is started when the tinc daemon with name @var{host} becomes unreachable.

@item @value{sysconfdir}/tinc/@var{netname}/host-up
This script is started when any host becomes reachable.

@item @value{sysconfdir}/tinc/@var{netname}/host-down
This script is started when any host becomes unreachable.

@item @value{sysconfdir}/tinc/@var{netname}/subnet-up
This script is started when a Subnet becomes reachable.
The Subnet and the node it belongs to are passed in environment variables.

@item @value{sysconfdir}/tinc/@var{netname}/subnet-down
This script is started when a Subnet becomes unreachable.

@item @value{sysconfdir}/tinc/@var{netname}/invitation-created
This script is started when a new invitation has been created.

@item @value{sysconfdir}/tinc/@var{netname}/invitation-accepted
This script is started when an invitation has been used.

@end table

@cindex environment variables
The scripts are started without command line arguments,
but can make use of certain environment variables.
Under UNIX like operating systems the names of environment variables must be preceded by a $ in scripts.
Under Windows, in @file{.bat} or @file{.cmd} files, they have to be put between % signs.

@table @env
@cindex NETNAME
@item NETNAME
If a netname was specified, this environment variable contains it.

@cindex NAME
@item NAME
Contains the name of this tinc daemon.

@cindex DEVICE
@item DEVICE
Contains the name of the virtual network device that tinc uses.

@cindex INTERFACE
@item INTERFACE
Contains the name of the virtual network interface that tinc uses.
This should be used for commands like ifconfig.

@cindex NODE
@item NODE
When a host becomes (un)reachable, this is set to its name.
If a subnet becomes (un)reachable, this is set to the owner of that subnet.

@cindex REMOTEADDRESS
@item REMOTEADDRESS
When a host becomes (un)reachable, this is set to its real address.

@cindex REMOTEPORT
@item REMOTEPORT
When a host becomes (un)reachable,
this is set to the port number it uses for communication with other tinc daemons.

@cindex SUBNET
@item SUBNET
When a subnet becomes (un)reachable, this is set to the subnet.

@cindex WEIGHT
@item WEIGHT
When a subnet becomes (un)reachable, this is set to the subnet weight.

@cindex INVITATION_FILE
@item INVITATION_FILE
When the @file{invitation-created} script is called,
this is set to the file where the invitation details will be stored.

@cindex INVITATION_URL
@item INVITATION_URL
When the @file{invitation-created} script is called,
this is set to the invitation URL that has been created.
@end table

Do not forget that under UNIX operating systems,
you have to make the scripts executable, using the command @samp{chmod a+x script}.


@c ==================================================================
@node       How to configure
@subsection How to configure

@subsubheading Step 1.  Creating initial configuration files.

The initial directory structure, configuration files and public/private keypairs are created using the following command:

@example
tinc -n @var{netname} init @var{name}
@end example

(You will need to run this as root, or use "sudo".)
This will create the configuration directory @file{@value{sysconfdir}/tinc/@var{netname}.},
and inside it will create another directory named @file{hosts/}.
In the configuration directory, it will create the file @file{tinc.conf} with the following contents:

@example
Name = @var{name}
@end example

It will also create private RSA and Ed25519 keys, which will be stored in the files @file{rsa_key.priv} and @file{ed25519_key.priv}.
It will also create a host configuration file @file{hosts/@var{name}},
which will contain the corresponding public RSA and Ed25519 keys.

Finally, on UNIX operating systems, it will create an executable script @file{tinc-up},
which will initially not do anything except warning that you should edit it.

@subsubheading Step 2.  Modifying the initial configuration.

Unless you want to use tinc in switch mode,
you should now configure which range of addresses you will use on the VPN.
Let's assume you will be part of a VPN which uses the address range 192.168.0.0/16,
and you yourself have a smaller portion of that range: 192.168.2.0/24.
Then you should run the following command:

@example
tinc -n @var{netname} add subnet 192.168.2.0/24
@end example

This will add a Subnet statement to your host configuration file.
Try opening the file @file{@value{sysconfdir}/tinc/@var{netname}/hosts/@var{name}} in an editor.
You should now see a file containing the public RSA and Ed25519 keys (which looks like a bunch of random characters),
and the following line at the bottom:

@example
Subnet = 192.168.2.0/24
@end example

If you will use more than one address range, you can add more Subnets.
For example, if you also use the IPv6 subnet fec0:0:0:2::/64, you can add it as well:

@example
tinc -n @var{netname} add subnet fec0:0:0:2::/24
@end example

This will add another line to the file @file{hosts/@var{name}}.
If you make a mistake, you can undo it by simply using @samp{del} instead of @samp{add}.

If you want other tinc daemons to create meta-connections to your daemon,
you should add your public IP address or hostname to your host configuration file.
For example, if your hostname is foo.example.org, run:

@example
tinc -n @var{netname} add address foo.example.org
@end example

If you already know to which daemons your daemon should make meta-connections,
you should configure that now as well.
Suppose you want to connect to a daemon named "bar", run:

@example
tinc -n @var{netname} add connectto bar
@end example

Note that you specify the Name of the other daemon here, not an IP address or hostname!
When you start tinc, and it tries to make a connection to "bar",
it will look for a host configuration file named @file{hosts/bar},
and will read Address statements and public keys from that file.

@subsubheading Step 2.  Exchanging configuration files.

If your daemon has a ConnectTo = bar statement in its @file{tinc.conf} file,
or if bar has a ConnectTo your daemon, then you both need each other's host configuration files.
You should send @file{hosts/@var{name}} to bar, and bar should send you his file which you should move to @file{hosts/bar}.
If you are on a UNIX platform, you can easily send an email containing the necessary information using the following command
(assuming the owner of bar has the email address bar@@example.org):

@example
tinc -n @var{netname} export | mail -s "My config file" bar@@example.org
@end example

If the owner of bar does the same to send his host configuration file to you,
you can probably pipe his email through the following command,
or you can just start this command in a terminal and copy&paste the email:

@example
tinc -n @var{netname} import
@end example

If you are the owner of bar yourself, and you have SSH access to that computer,
you can also swap the host configuration files using the following command:

@example
tinc -n @var{netname} export \
    | ssh bar.example.org tinc -n @var{netname} exchange \
    | tinc -n @var{netname} import
@end example

You should repeat this for all nodes you ConnectTo, or which ConnectTo you.
However, remember that you do not need to ConnectTo all nodes in the VPN;
it is only necessary to create one or a few meta-connections,
after the connections are made tinc will learn about all the other nodes in the VPN,
and will automatically make other connections as necessary.


@c ==================================================================
@node    Network interfaces
@section Network interfaces

Before tinc can start transmitting data over the tunnel, it must
set up the virtual network interface.

First, decide which IP addresses you want to have associated with these
devices, and what network mask they must have.

Tinc will open a virtual network device (@file{/dev/tun}, @file{/dev/tap0} or similar),
which will also create a network interface called something like @samp{tun0}, @samp{tap0}.
If you are using the Linux tun/tap driver, the network interface will by default have the same name as the @var{netname}.
Under Windows you can change the name of the network interface from the Network Connections control panel.

@cindex tinc-up
You can configure the network interface by putting ordinary ifconfig, route, and other commands
to a script named @file{@value{sysconfdir}/tinc/@var{netname}/tinc-up}.
When tinc starts, this script will be executed. When tinc exits, it will execute the script named
@file{@value{sysconfdir}/tinc/@var{netname}/tinc-down}, but normally you don't need to create that script.
You can manually open the script in an editor, or use the following command:

@example
tinc -n @var{netname} edit tinc-up
@end example

An example @file{tinc-up} script, that would be appropriate for the scenario in the previous section, is:

@example
#!/bin/sh
ifconfig $INTERFACE 192.168.2.1 netmask 255.255.0.0
ip addr add fec0:0:0:2::/48 dev $INTERFACE
@end example

The first command gives the interface an IPv4 address and a netmask.
The kernel will also automatically add an IPv4 route to this interface, so normally you don't need
to add route commands to the @file{tinc-up} script.
The kernel will also bring the interface up after this command.
@cindex netmask
The netmask is the mask of the @emph{entire} VPN network, not just your
own subnet.
The second command gives the interface an IPv6 address and netmask,
which will also automatically add an IPv6 route.
If you only want to use "ip addr" commands on Linux, don't forget that it doesn't bring the interface up, unlike ifconfig,
so you need to add @samp{ip link set $INTERFACE up} in that case.

The exact syntax of the ifconfig and route commands differs from platform to platform.
You can look up the commands for setting addresses and adding routes in @ref{Platform specific information},
but it is best to consult the manpages of those utilities on your platform.


@c ==================================================================
@node    Example configuration
@section Example configuration


@cindex example
Imagine the following situation.  Branch A of our example `company' wants to connect
three branch offices in B, C and D using the Internet.  All four offices
have a 24/7 connection to the Internet.

A is going to serve as the center of the network.  B and C will connect
to A, and D will connect to C.  Each office will be assigned their own IP
network, 10.x.0.0.

@example
A: net 10.1.0.0 mask 255.255.0.0 gateway 10.1.54.1 internet IP 1.2.3.4
B: net 10.2.0.0 mask 255.255.0.0 gateway 10.2.1.12 internet IP 2.3.4.5
C: net 10.3.0.0 mask 255.255.0.0 gateway 10.3.69.254 internet IP 3.4.5.6
D: net 10.4.0.0 mask 255.255.0.0 gateway 10.4.3.32 internet IP 4.5.6.7
@end example

Here, ``gateway'' is the VPN IP address of the machine that is running the
tincd, and ``internet IP'' is the IP address of the firewall, which does not
need to run tincd, but it must do a port forwarding of TCP and UDP on port
655 (unless otherwise configured).

In this example, it is assumed that eth0 is the interface that points to
the inner (physical) LAN of the office, although this could also be the
same as the interface that leads to the Internet.  The configuration of
the real interface is also shown as a comment, to give you an idea of
how these example host is set up. All branches use the netname `company'
for this particular VPN.

Each branch is set up using the @samp{tinc init} and @samp{tinc config} commands,
here we just show the end results:

@subsubheading For Branch A

@emph{BranchA} would be configured like this:

In @file{@value{sysconfdir}/tinc/company/tinc-up}:

@example
#!/bin/sh

# Real interface of internal network:
# ifconfig eth0 10.1.54.1 netmask 255.255.0.0

ifconfig $INTERFACE 10.1.54.1 netmask 255.0.0.0
@end example

and in @file{@value{sysconfdir}/tinc/company/tinc.conf}:

@example
Name = BranchA
@end example

On all hosts, @file{@value{sysconfdir}/tinc/company/hosts/BranchA} contains:

@example
Subnet = 10.1.0.0/16
Address = 1.2.3.4

-----BEGIN RSA PUBLIC KEY-----
...
-----END RSA PUBLIC KEY-----
@end example

Note that the IP addresses of eth0 and the VPN interface are the same.
This is quite possible, if you make sure that the netmasks of the interfaces are different.
It is in fact recommended to give both real internal network interfaces and VPN interfaces the same IP address,
since that will make things a lot easier to remember and set up.


@subsubheading For Branch B

In @file{@value{sysconfdir}/tinc/company/tinc-up}:

@example
#!/bin/sh

# Real interface of internal network:
# ifconfig eth0 10.2.43.8 netmask 255.255.0.0

ifconfig $INTERFACE 10.2.1.12 netmask 255.0.0.0
@end example

and in @file{@value{sysconfdir}/tinc/company/tinc.conf}:

@example
Name = BranchB
ConnectTo = BranchA
@end example

Note here that the internal address (on eth0) doesn't have to be the
same as on the VPN interface.  Also, ConnectTo is given so that this node will
always try to connect to BranchA.

On all hosts, in @file{@value{sysconfdir}/tinc/company/hosts/BranchB}:

@example
Subnet = 10.2.0.0/16
Address = 2.3.4.5

-----BEGIN RSA PUBLIC KEY-----
...
-----END RSA PUBLIC KEY-----
@end example


@subsubheading For Branch C

In @file{@value{sysconfdir}/tinc/company/tinc-up}:

@example
#!/bin/sh

# Real interface of internal network:
# ifconfig eth0 10.3.69.254 netmask 255.255.0.0

ifconfig $INTERFACE 10.3.69.254 netmask 255.0.0.0
@end example

and in @file{@value{sysconfdir}/tinc/company/tinc.conf}:

@example
Name = BranchC
ConnectTo = BranchA
@end example

C already has another daemon that runs on port 655, so they have to
reserve another port for tinc. It knows the portnumber it has to listen on
from it's own host configuration file.

On all hosts, in @file{@value{sysconfdir}/tinc/company/hosts/BranchC}:

@example
Address = 3.4.5.6
Subnet = 10.3.0.0/16
Port = 2000

-----BEGIN RSA PUBLIC KEY-----
...
-----END RSA PUBLIC KEY-----
@end example


@subsubheading For Branch D

In @file{@value{sysconfdir}/tinc/company/tinc-up}:

@example
#!/bin/sh

# Real interface of internal network:
# ifconfig eth0 10.4.3.32 netmask 255.255.0.0

ifconfig $INTERFACE 10.4.3.32 netmask 255.0.0.0
@end example

and in @file{@value{sysconfdir}/tinc/company/tinc.conf}:

@example
Name = BranchD
ConnectTo = BranchC
@end example

D will be connecting to C, which has a tincd running for this network on
port 2000. It knows the port number from the host configuration file.

On all hosts, in @file{@value{sysconfdir}/tinc/company/hosts/BranchD}:

@example
Subnet = 10.4.0.0/16
Address = 4.5.6.7

-----BEGIN RSA PUBLIC KEY-----
...
-----END RSA PUBLIC KEY-----
@end example

@subsubheading Key files

A, B, C and D all have their own public/private keypairs:

The private RSA key is stored in @file{@value{sysconfdir}/tinc/company/rsa_key.priv},
the private Ed25519 key is stored in @file{@value{sysconfdir}/tinc/company/ed25519_key.priv},
and the public RSA and Ed25519 keys are put into the host configuration file in the @file{@value{sysconfdir}/tinc/company/hosts/} directory.

@subsubheading Starting

After each branch has finished configuration and they have distributed
the host configuration files amongst them, they can start their tinc daemons.
They don't necessarily have to wait for the other branches to have started
their daemons, tinc will try connecting until they are available.


@c ==================================================================
@node    Running tinc
@chapter Running tinc

If everything else is done, you can start tinc by typing the following command:

@example
tinc -n @var{netname} start
@end example

@cindex daemon
Tinc will detach from the terminal and continue to run in the background like a good daemon.
If there are any problems however you can try to increase the debug level
and look in the syslog to find out what the problems are.

@menu
* Runtime options::
* Signals::
* Debug levels::
* Solving problems::
* Error messages::
* Sending bug reports::
@end menu


@c ==================================================================
@node    Runtime options
@section Runtime options

Besides the settings in the configuration file, tinc also accepts some
command line options.

@cindex command line
@cindex runtime options
@cindex options
@c from the manpage
@table @option
@item -c, --config=@var{path}
Read configuration options from the directory @var{path}.  The default is
@file{@value{sysconfdir}/tinc/@var{netname}/}.

@item -D, --no-detach
Don't fork and detach.
This will also disable the automatic restart mechanism for fatal errors.

@cindex debug level
@item -d, --debug=@var{level}
Set debug level to @var{level}.  The higher the debug level, the more gets
logged.  Everything goes via syslog.

@item -n, --net=@var{netname}
Use configuration for net @var{netname}.
This will let tinc read all configuration files from
@file{@value{sysconfdir}/tinc/@var{netname}/}.
Specifying . for @var{netname} is the same as not specifying any @var{netname}.
@xref{Multiple networks}.

@item --pidfile=@var{filename}
Store a cookie in @var{filename} which allows tinc to authenticate.
If unspecified, the default is
@file{@value{localstatedir}/run/tinc.@var{netname}.pid}.

@item -o, --option=[@var{HOST}.]@var{KEY}=@var{VALUE}
Without specifying a @var{HOST}, this will set server configuration variable @var{KEY} to @var{VALUE}.
If specified as @var{HOST}.@var{KEY}=@var{VALUE},
this will set the host configuration variable @var{KEY} of the host named @var{HOST} to @var{VALUE}.
This option can be used more than once to specify multiple configuration variables.

@item -L, --mlock
Lock tinc into main memory.
This will prevent sensitive data like shared private keys to be written to the system swap files/partitions.

This option is not supported on all platforms.

@item --logfile[=@var{file}]
Write log entries to a file instead of to the system logging facility.
If @var{file} is omitted, the default is @file{@value{localstatedir}/log/tinc.@var{netname}.log}.

@item --bypass-security
Disables encryption and authentication.
Only useful for debugging.

@item -R, --chroot
Change process root directory to the directory where the config file is
located (@file{@value{sysconfdir}/tinc/@var{netname}/} as determined by
-n/--net option or as given by -c/--config option), for added security.
The chroot is performed after all the initialization is done, after
writing pid files and opening network sockets.

Note that this option alone does not do any good without -U/--user, below.

Note also that tinc can't run scripts anymore (such as tinc-down or host-up),
unless it's setup to be runnable inside chroot environment.

This option is not supported on all platforms.
@item -U, --user=@var{user}
Switch to the given @var{user} after initialization, at the same time as
chroot is performed (see --chroot above).  With this option tinc drops
privileges, for added security.

This option is not supported on all platforms.

@item --help
Display a short reminder of these runtime options and terminate.

@item --version
Output version information and exit.

@end table

@c ==================================================================
@node    Signals
@section Signals

@cindex signals
You can also send the following signals to a running tincd process:

@c from the manpage
@table @samp

@item ALRM
Forces tinc to try to connect to all uplinks immediately.
Usually tinc attempts to do this itself,
but increases the time it waits between the attempts each time it failed,
and if tinc didn't succeed to connect to an uplink the first time after it started,
it defaults to the maximum time of 15 minutes.

@item HUP
Partially rereads configuration files.
Connections to hosts whose host config file are removed are closed.
New outgoing connections specified in @file{tinc.conf} will be made.
If the --logfile option is used, this will also close and reopen the log file,
useful when log rotation is used.

@end table

@c ==================================================================
@node    Debug levels
@section Debug levels

@cindex debug levels
The tinc daemon can send a lot of messages to the syslog.
The higher the debug level, the more messages it will log.
Each level inherits all messages of the previous level:

@c from the manpage
@table @samp

@item 0
This will log a message indicating tinc has started along with a version number.
It will also log any serious error.

@item 1
This will log all connections that are made with other tinc daemons.

@item 2
This will log status and error messages from scripts and other tinc daemons.

@item 3
This will log all requests that are exchanged with other tinc daemons. These include
authentication, key exchange and connection list updates.

@item 4
This will log a copy of everything received on the meta socket.

@item 5
This will log all network traffic over the virtual private network.

@end table

@c ==================================================================
@node    Solving problems
@section Solving problems

If tinc starts without problems, but if the VPN doesn't work, you will have to find the cause of the problem.
The first thing to do is to start tinc with a high debug level in the foreground,
so you can directly see everything tinc logs:

@example
tincd -n @var{netname} -d5 -D
@end example

If tinc does not log any error messages, then you might want to check the following things:

@itemize
@item @file{tinc-up} script
Does this script contain the right commands?
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.

@item Subnet
Does the Subnet (or Subnets) in the host configuration file of this host match the portion of the VPN that belongs to this host?

@item Firewalls and NATs
Do you have a firewall or a NAT device (a masquerading firewall or perhaps an ADSL router that performs masquerading)?
If so, check that it allows TCP and UDP traffic on port 655.
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.
You can add @samp{TCPOnly = yes} to your host config file to force tinc to only use a single TCP connection,
this works through most firewalls and NATs.

@end itemize


@c ==================================================================
@node    Error messages
@section Error messages

What follows is a list of the most common error messages you might find in the logs.
Some of them will only be visible if the debug level is high enough.

@table @samp
@item Could not open /dev/tap0: No such device

@itemize
@item You forgot to `modprobe netlink_dev' or `modprobe ethertap'.
@item You forgot to compile `Netlink device emulation' in the kernel.
@end itemize

@item Can't write to /dev/net/tun: No such device

@itemize
@item You forgot to `modprobe tun'.
@item You forgot to compile `Universal TUN/TAP driver' in the kernel.
@item The tun device is located somewhere else in @file{/dev/}.
@end itemize

@item Network address and prefix length do not match!

@itemize
@item The Subnet field must contain a @emph{network} address, trailing bits should be 0.
@item If you only want to use one IP address, set the netmask to /32.
@end itemize

@item Error reading RSA key file `rsa_key.priv': No such file or directory

@itemize
@item You forgot to create a public/private keypair.
@item Specify the complete pathname to the private key file with the @samp{PrivateKeyFile} option.
@end itemize

@item Warning: insecure file permissions for RSA private key file `rsa_key.priv'!

@itemize
@item The private key file is readable by users other than root.
Use chmod to correct the file permissions.
@end itemize

@item Creating metasocket failed: Address family not supported

@itemize
@item By default tinc tries to create both IPv4 and IPv6 sockets.
On some platforms this might not be implemented.
If the logs show @samp{Ready} later on, then at least one metasocket was created,
and you can ignore this message.
You can add @samp{AddressFamily = ipv4} to @file{tinc.conf} to prevent this from happening.
@end itemize

@item Cannot route packet: unknown IPv4 destination 1.2.3.4

@itemize
@item You try to send traffic to a host on the VPN for which no Subnet is known.
@item If it is a broadcast address (ending in .255), it probably is a samba server or a Windows host sending broadcast packets.
You can ignore it.
@end itemize

@item Cannot route packet: ARP request for unknown address 1.2.3.4

@itemize
@item You try to send traffic to a host on the VPN for which no Subnet is known.
@end itemize

@item Packet with destination 1.2.3.4 is looping back to us!

@itemize
@item Something is not configured right. Packets are being sent out to the
virtual network device, but according to the Subnet directives in your host configuration
file, those packets should go to your own host. Most common mistake is that
you have a Subnet line in your host configuration file with a prefix length which is
just as large as the prefix of the virtual network interface. The latter should in almost all
cases be larger. Rethink your configuration.
Note that you will only see this message if you specified a debug
level of 5 or higher!
@item Chances are that a @samp{Subnet = ...} line in the host configuration file of this tinc daemon is wrong.
Change it to a subnet that is accepted locally by another interface,
or if that is not the case, try changing the prefix length into /32.
@end itemize

@item Node foo (1.2.3.4) is not reachable

@itemize
@item Node foo does not have a connection anymore, its tinc daemon is not running or its connection to the Internet is broken.
@end itemize

@item Received UDP packet from unknown source 1.2.3.4 (port 12345)

@itemize
@item If you see this only sporadically, it is harmless and caused by a node sending packets using an old key.
@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.
You can add @samp{TCPOnly = yes} to host configuration files to force all VPN traffic to go over a TCP connection.
@end itemize

@item Got bad/bogus/unauthorized REQUEST from foo (1.2.3.4 port 12345)

@itemize
@item Node foo does not have the right public/private keypair.
Generate new keypairs and distribute them again.
@item An attacker tries to gain access to your VPN.
@item A network error caused corruption of metadata sent from foo.
@end itemize

@end table

@c ==================================================================
@node    Sending bug reports
@section Sending bug reports

If you really can't find the cause of a problem, or if you suspect tinc is not working right,
you can send us a bugreport, see @ref{Contact information}.
Be sure to include the following information in your bugreport:

@itemize
@item A clear description of what you are trying to achieve and what the problem is.
@item What platform (operating system, version, hardware architecture) and which version of tinc you use.
@item If compiling tinc fails, a copy of @file{config.log} and the error messages you get.
@item Otherwise, a copy of @file{tinc.conf}, @file{tinc-up} and all files in the @file{hosts/} directory.
@item The output of the commands @samp{ifconfig -a} and @samp{route -n} (or @samp{netstat -rn} if that doesn't work).
@item The output of any command that fails to work as it should (like ping or traceroute).
@end itemize

@c ==================================================================
@node    Controlling tinc
@chapter Controlling tinc

@cindex command line interface
You can start, stop, control and inspect a running tincd through the tinc
command. A quick example:

@example
tinc -n @var{netname} reload
@end example

@cindex shell
If tinc is started without a command, it will act as a shell; it will display a
prompt, and commands can be entered on the prompt. If tinc is compiled with
libreadline, history and command completion are available on the prompt. One
can also pipe a script containing commands through tinc. In that case, lines
starting with a # symbol will be ignored.

@menu
* tinc runtime options::
* tinc environment variables::
* tinc commands::
* tinc examples::
* tinc top::
@end menu


@c ==================================================================
@node    tinc runtime options
@section tinc runtime options

@c from the manpage
@table @option
@item -c, --config=@var{path}
Read configuration options from the directory @var{path}.  The default is
@file{@value{sysconfdir}/tinc/@var{netname}/}.

@item -n, --net=@var{netname}
Use configuration for net @var{netname}. @xref{Multiple networks}.

@item --pidfile=@var{filename}
Use the cookie from @var{filename} to authenticate with a running tinc daemon.
If unspecified, the default is
@file{@value{localstatedir}/run/tinc.@var{netname}.pid}.

@item --force
Force some commands to work despite warnings.

@item --help
Display a short reminder of runtime options and commands, then terminate.

@item --version
Output version information and exit.

@end table

@c ==================================================================
@node    tinc environment variables
@section tinc environment variables

@table @env
@cindex NETNAME
@item NETNAME
If no netname is specified on the command line with the @option{-n} option,
the value of this environment variable is used.
@end table

@c ==================================================================
@node    tinc commands
@section tinc commands

@c from the manpage
@table @code

@cindex init
@item init [@var{name}]
Create initial configuration files and RSA and Ed25519 keypairs with default length.
If no @var{name} for this node is given, it will be asked for.

@cindex get
@item get @var{variable}
Print the current value of configuration variable @var{variable}.
If more than one variable with the same name exists,
the value of each of them will be printed on a separate line.

@cindex set
@item set @var{variable} @var{value}
Set configuration variable @var{variable} to the given @var{value}.
All previously existing configuration variables with the same name are removed.
To set a variable for a specific host, use the notation @var{host}.@var{variable}.

@cindex add
@item add @var{variable} @var{value}
As above, but without removing any previously existing configuration variables.
If the variable already exists with the given value, nothing happens.

@cindex del
@item del @var{variable} [@var{value}]
Remove configuration variables with the same name and @var{value}.
If no @var{value} is given, all configuration variables with the same name will be removed.

@cindex edit
@item edit @var{filename}
Start an editor for the given configuration file.
You do not need to specify the full path to the file.

@cindex export
@item export
Export the host configuration file of the local node to standard output.

@cindex export-all
@item export-all
Export all host configuration files to standard output.

@cindex import
@item import
Import host configuration file(s) generated by the tinc export command from standard input.
Already existing host configuration files are not overwritten unless the option --force is used.

@cindex exchange
@item exchange
The same as export followed by import.

@cindex exchange-all
@item exchange-all
The same as export-all followed by import.

@cindex invite
@item invite @var{name}
Prepares an invitation for a new node with the given @var{name},
and prints a short invitation URL that can be used with the join command.

@cindex join
@item join [@var{URL}]
Join an existing VPN using an invitation URL created using the invite command.
If no @var{URL} is given, it will be read from standard input.

@cindex start
@item start [tincd options]
Start @samp{tincd}, optionally with the given extra options.

@cindex stop
@item stop
Stop @samp{tincd}.

@cindex restart
@item restart [tincd options]
Restart @samp{tincd}, optionally with the given extra options.

@cindex reload
@item reload
Partially rereads configuration files. Connections to hosts whose host
config files are removed are closed. New outgoing connections specified
in @file{tinc.conf} will be made.

@cindex pid
@item pid
Shows the PID of the currently running @samp{tincd}.

@cindex generate-keys
@item generate-keys [@var{bits}]
Generate both RSA and Ed25519 keypairs (see below) and exit.
tinc will ask where you want to store the files, but will default to the
configuration directory (you can use the -c or -n option).

@cindex generate-ed25519-keys
@item generate-ed25519-keys
Generate public/private Ed25519 keypair and exit.

@cindex generate-rsa-keys
@item generate-rsa-keys [@var{bits}]
Generate public/private RSA keypair and exit.  If @var{bits} is omitted, the
default length will be 2048 bits.  When saving keys to existing files, tinc
will not delete the old keys; you have to remove them manually.

@cindex dump
@item dump [reachable] nodes
Dump a list of all known nodes in the VPN.
If the reachable keyword is used, only lists reachable nodes.

@item dump edges
Dump a list of all known connections in the VPN.

@item dump subnets
Dump a list of all known subnets in the VPN.

@item dump connections
Dump a list of all meta connections with ourself.

@cindex graph
@item dump graph | digraph
Dump a graph of the VPN in dotty format.
Nodes are colored according to their reachability:
red nodes are unreachable, orange nodes are indirectly reachable, green nodes are directly reachable.
Black nodes are either directly or indirectly reachable, but direct reachability has not been tried yet.

@item dump invitations
Dump a list of outstanding invitations.
The filename of the invitation, as well as the name of the node that is being invited is shown for each invitation.

@cindex info
@item info @var{node} | @var{subnet} | @var{address}
Show information about a particular @var{node}, @var{subnet} or @var{address}.
If an @var{address} is given, any matching subnet will be shown.

@cindex purge
@item purge
Purges all information remembered about unreachable nodes.

@cindex debug
@item debug @var{level}
Sets debug level to @var{level}.

@cindex log
@item log [@var{level}]
Capture log messages from a running tinc daemon.
An optional debug level can be given that will be applied only for log messages sent to tinc.

@cindex retry
@item retry
Forces tinc to try to connect to all uplinks immediately.
Usually tinc attempts to do this itself,
but increases the time it waits between the attempts each time it failed,
and if tinc didn't succeed to connect to an uplink the first time after it started,
it defaults to the maximum time of 15 minutes.

@cindex disconnect
@item disconnect @var{node}
Closes the meta connection with the given @var{node}.

@cindex top
@item top
If tinc is compiled with libcurses support, this will display live traffic statistics for all the known nodes,
similar to the UNIX top command.
See below for more information.

@cindex pcap
@item pcap
Dump VPN traffic going through the local tinc node in pcap-savefile format to standard output,
from where it can be redirected to a file or piped through a program that can parse it directly,
such as tcpdump.

@cindex network
@item network [@var{netname}]
If @var{netname} is given, switch to that network.
Otherwise, display a list of all networks for which configuration files exist.

@cindex fsck
@item fsck
This will check the configuration files for possible problems,
such as unsafe file permissions, missing executable bit on script,
unknown and obsolete configuration variables, wrong public and/or private keys, and so on.

When problems are found, this will be printed on a line with WARNING or ERROR in front of it.
Most problems must be corrected by the user itself, however in some cases (like file permissions and missing public keys),
tinc will ask if it should fix the problem.

@cindex sign
@item sign [@var{filename}]
Sign a file with the local node's private key.
If no @var{filename} is given, the file is read from standard input.
The signed file is written to standard output.

@cindex verify
@item verify @var{name} [@var{filename}]

Check the signature of a file against a node's public key.
The @var{name} of the node must be given,
or can be "." to check against the local node's public key,
or "*" to allow a signature from any node whose public key is known.
If no @var{filename} is given, the file is read from standard input.
If the verification is succesful, a copy of the input with the signature removed is written to standard output, and the exit code will be zero.
If the verification failed, nothing will be written to standard output, and the exit code will be non-zero.

@end table

@c ==================================================================
@node    tinc examples
@section tinc examples

Examples of some commands:

@example
tinc -n vpn dump graph | circo -Txlib
tinc -n vpn pcap | tcpdump -r -
tinc -n vpn top
@end example

Examples of changing the configuration using tinc:

@example
tinc -n vpn init foo
tinc -n vpn add Subnet 192.168.1.0/24
tinc -n vpn add bar.Address bar.example.com
tinc -n vpn add ConnectTo bar
tinc -n vpn export | gpg --clearsign | mail -s "My config" vpnmaster@@example.com
@end example

@c ==================================================================
@node    tinc top
@section tinc top

@cindex top
The top command connects to a running tinc daemon and repeatedly queries its per-node traffic counters.
It displays a list of all the known nodes in the left-most column,
and the amount of bytes and packets read from and sent to each node in the other columns.
By default, the information is updated every second.
The behaviour of the top command can be changed using the following keys:

@table @key

@item s
Change the interval between updates.
After pressing the @key{s} key, enter the desired interval in seconds, followed by enter.
Fractional seconds are honored.
Intervals lower than 0.1 seconds are not allowed.

@item c
Toggle between displaying current traffic rates (in packets and bytes per second)
and cummulative traffic (total packets and bytes since the tinc daemon started).

@item n
Sort the list of nodes by name.

@item i
Sort the list of nodes by incoming amount of bytes.

@item I
Sort the list of nodes by incoming amount of packets.

@item o
Sort the list of nodes by outgoing amount of bytes.

@item O
Sort the list of nodes by outgoing amount of packets.

@item t
Sort the list of nodes by sum of incoming and outgoing amount of bytes.

@item T
Sort the list of nodes by sum of incoming and outgoing amount of packets.

@item b
Show amount of traffic in bytes.

@item k
Show amount of traffic in kilobytes.

@item M
Show amount of traffic in megabytes.

@item G
Show amount of traffic in gigabytes.

@item q
Quit.

@end table


@c ==================================================================
@node    Invitations
@chapter Invitations

Invitations are an easy way to add new nodes to an existing VPN.  Invitations
can be created on an existing node using the @code{tinc invite} command, which
generates a relatively short URL which can be given to someone else, who uses
the @code{tinc join} command to automatically set up tinc so it can connect to
the inviting node.  The next sections describe how invitations actually work,
and how to further automate the invitations.

@menu
* How invitations work::
* Invitation file format::
* Writing an invitation-created script::
@end menu


@c ==================================================================
@node    How invitations work
@section How invitations work

When an invitation is created on a node (which from now on we will call the
server) using the @code{tinc invite} command, an invitation file is created
that contains all the information necessary for the invitee (which we will call
the client) to create its configuration files. The invitation file is stays on
the server, but a URL is generated that has enough information for the client
to contact the server and to retrieve the invitation file. The whole URL is
around 80 characters long and looks like this:

@example
server.example.org:12345/cW1NhLHS-1WPFlcFio8ztYHvewTTKYZp8BjEKg3vbMtDz7w4
@end example

It is composed of four parts:

@example
hostname : port / keyhash cookie
@end example

The hostname and port tell the client how to reach the tinc daemon on the server.
The part after the slash looks like one blob, but is composed of two parts.
The keyhash is the hash of the public key of the server.
The cookie is a shared secret that identifies the client to the server.

When the client connects to the server in order to join the VPN, the client and
server will exchange temporary public keys. The client verifies that the hash
of the server's public key matches the keyhash from the invitation URL. If
not, it will immediately exit with an error. Otherwise, an ECDH exchange will
happen so the client and server can communicate privately with each other. The
client will then present the cookie to the server. The server uses this to
look up the corresponding invitation file it generated earlier. If it exists,
it will send the invitation file to the client. The client will also create a
permanent public key, and send it to the server. After the exchange is
completed, the connection is broken. The server creates a host config file for
the client containing the client's permanent public key, and the client creates
tinc.conf, host config files and possibly a tinc-up script based on the
information in the invitation file.

It is important that the invitation URL is kept secret until it is used; if
another person gets a copy of the invitation URL before the real client runs
the @code{tinc join} command, then that other person can try to join the VPN.


@c ==================================================================
@node    Invitation file format
@section Invitation file format

The contents of an invitation file that is generated by the @code{tinc invite}
command looks like this:

@example
Name = client
Netname = vpn
ConnectTo = server
#-------------------------------------#
Name = server
Ed25519PublicKey = augbnwegoij123587...
Address = server.example.com
@end example

The file is basically a concatenation of several host config blocks. Each host
config block starts with @code{Name = ...}.  Lines that look like @code{#---#}
are not important, it just makes it easier for humans to read the file.

The first host config block is always the one representing the invitee. So the
first Name statement determines the name that the invitee will get. From the
first block, the @file{tinc.conf} and @file{hosts/client} files will be
generated; the @code{tinc join} command on the client will automatically
separate statements based on whether they should be in @file{tinc.conf} or in a
host config file. Some statements are special and are treated differently:

@table @asis
@item Netname = <@var{netname}>
This is a hint to the invitee which netname to use for the VPN.  It is used if
the invitee did not already specify a netname, and if there is no pre-existing
configuration with the same netname.

@cindex Ifconfig
@item Ifconfig = <@var{address}[/@var{netmask}] | dhcp | dhcp6 | slaac>
This is a hint for generating a @file{tinc-up} script.
If an address is specified, a command will be added to @file{tinc-up} so the VPN interface will be configured to have the given address.
If it is the word "dhcp", a command will be added to start a DHCP client on the VPN interface.
If it is the word dhcpv6, it will be a DHCPv6 client.
If it is "slaac", then it will add commands to enable IPv6 stateless address autoconfiguration.
It is also possible to specify a MAC address, in which case a command will be added to set the MAC address of the VPN interface.

The exact commands added to the @file{tinc-up} script depends on the operating system the client is using.
Multiple Ifconfig statements can be specified, however one should only use one Ifconfig statement per address family.

@cindex Route
@item Route = <@var{address}[/@var{netmask}]> [<@var{gateway}>]
This is a hint for generating a @file{tinc-up} script.
Route statements are similar to Ifconfig statements, but add routes instead of addresses.
These only allow IPv4 and IPv6 routes.
If no gateway address is specified, the route is directed to the VPN interface.
In general, a gateway is only necessary when running tinc in switch mode.
@end table

Subsequent host config blocks are copied verbatim into their respective files
in @file{hosts/}. The invitation file generated by @code{tinc invite} will
normally only contain two blocks; one for the client and one for the server.


@c ==================================================================
@node    Writing an invitation-created script
@section Writing an invitation-created script

When an invitation is generated, the "invitation-created" script is called (if
it exists) right after the invitation file is written, but before the URL has
been written to stdout. This allows one to change the invitation file
automatically before the invitation URL is passed to the invitee. Here is an
example shell script that aproximately recreates the default invitation file:

@example
#!/bin/sh

cat >$INVITATION_FILE <<EOF
Name = $NODE
Netname = $NETNAME
ConnectTo = $NAME
#----------------#
EOF

tinc export >>$INVITATION_FILE
@end example

You can add more ConnectTo statements, and change `tinc export` to `tinc
export-all` for example. But you can also use the script to automatically hand
out a Subnet to the invitee. Note that the script doesn't have to be a shell script,
you can use any language, it just has to be executable.


@c ==================================================================
@node    Technical information
@chapter Technical information


@menu
* The connection::
* The meta-protocol::
* Security::
@end menu


@c ==================================================================
@node    The connection
@section The connection

@cindex connection
Tinc is a daemon that takes VPN data and transmit that to another host
computer over the existing Internet infrastructure.

@menu
* The UDP tunnel::
* The meta-connection::
@end menu


@c ==================================================================
@node    The UDP tunnel
@subsection The UDP tunnel

@cindex virtual network device
@cindex frame type
The data itself is read from a character device file, the so-called
@emph{virtual network device}.  This device is associated with a network
interface.  Any data sent to this interface can be read from the device,
and any data written to the device gets sent from the interface.
There are two possible types of virtual network devices:
`tun' style, which are point-to-point devices which can only handle IPv4 and/or IPv6 packets,
and `tap' style, which are Ethernet devices and handle complete Ethernet frames.

So when tinc reads an Ethernet frame from the device, it determines its
type. When tinc is in it's default routing mode, it can handle IPv4 and IPv6
packets. Depending on the Subnet lines, it will send the packets off to their destination IP address.
In the `switch' and `hub' mode, tinc will use broadcasts and MAC address discovery
to deduce the destination of the packets.
Since the latter modes only depend on the link layer information,
any protocol that runs over Ethernet is supported (for instance IPX and Appletalk).
However, only `tap' style devices provide this information.

After the destination has been determined,
the packet will be compressed (optionally),
a sequence number will be added to the packet,
the packet will then be encrypted
and a message authentication code will be appended.

@cindex encapsulating
@cindex UDP
When that is done, time has come to actually transport the
packet to the destination computer.  We do this by sending the packet
over an UDP connection to the destination host.  This is called
@emph{encapsulating}, the VPN packet (though now encrypted) is
encapsulated in another IP datagram.

When the destination receives this packet, the same thing happens, only
in reverse.  So it checks the message authentication code, decrypts the contents of the UDP datagram,
checks the sequence number
and writes the decrypted information to its own virtual network device.

If the virtual network device is a `tun' device (a point-to-point tunnel),
there is no problem for the kernel to accept a packet.
However, if it is a `tap' device (this is the only available type on FreeBSD),
the destination MAC address must match that of the virtual network interface.
If tinc is in it's default routing mode, ARP does not work, so the correct destination MAC
can not be known by the sending host.
Tinc solves this by letting the receiving end detect the MAC address of its own virtual network interface
and overwriting the destination MAC address of the received packet.

In switch or hub modes ARP does work so the sender already knows the correct destination MAC address.
In those modes every interface should have a unique MAC address, so make sure they are not the same.
Because switch and hub modes rely on MAC addresses to function correctly,
these modes cannot be used on the following operating systems which don't have a `tap' style virtual network device:
OpenBSD, NetBSD, Darwin and Solaris.


@c ==================================================================
@node    The meta-connection
@subsection The meta-connection

Having only a UDP connection available is not enough.  Though suitable
for transmitting data, we want to be able to reliably send other
information, such as routing and session key information to somebody.

@cindex TCP
TCP is a better alternative, because it already contains protection
against information being lost, unlike UDP.

So we establish two connections.  One for the encrypted VPN data, and one
for other information, the meta-data.  Hence, we call the second
connection the meta-connection.  We can now be sure that the
meta-information doesn't get lost on the way to another computer.

@cindex data-protocol
@cindex meta-protocol
Like with any communication, we must have a protocol, so that everybody
knows what everything stands for, and how she should react.  Because we
have two connections, we also have two protocols.  The protocol used for
the UDP data is the ``data-protocol,'' the other one is the
``meta-protocol.''

The reason we don't use TCP for both protocols is that UDP is much
better for encapsulation, even while it is less reliable.  The real
problem is that when TCP would be used to encapsulate a TCP stream
that's on the private network, for every packet sent there would be
three ACKs sent instead of just one.  Furthermore, if there would be
a timeout, both TCP streams would sense the timeout, and both would
start re-sending packets.


@c ==================================================================
@node    The meta-protocol
@section The meta-protocol

The meta protocol is used to tie all tinc daemons together, and
exchange information about which tinc daemon serves which virtual
subnet.

The meta protocol consists of requests that can be sent to the other
side.  Each request has a unique number and several parameters.  All
requests are represented in the standard ASCII character set.  It is
possible to use tools such as telnet or netcat to connect to a tinc
daemon started with the --bypass-security option
and to read and write requests by hand, provided that one
understands the numeric codes sent.

The authentication scheme is described in @ref{Security}. After a
successful authentication, the server and the client will exchange all the
information about other tinc daemons and subnets they know of, so that both
sides (and all the other tinc daemons behind them) have their information
synchronised.

@cindex ADD_EDGE
@cindex ADD_SUBNET
@example
message
------------------------------------------------------------------
ADD_EDGE node1 node2 21.32.43.54 655 222 0
          |     |        |       |   |  +-> options
          |     |        |       |   +----> weight
          |     |        |       +--------> UDP port of node2
          |     |        +----------------> real address of node2
          |     +-------------------------> name of destination node
          +-------------------------------> name of source node

ADD_SUBNET node 192.168.1.0/24
            |         |     +--> prefixlength
            |         +--------> network address
            +------------------> owner of this subnet
------------------------------------------------------------------
@end example

The ADD_EDGE messages are to inform other tinc daemons that a connection between
two nodes exist. The address of the destination node is available so that
VPN packets can be sent directly to that node.

The ADD_SUBNET messages inform other tinc daemons that certain subnets belong
to certain nodes. tinc will use it to determine to which node a VPN packet has
to be sent.

@cindex DEL_EDGE
@cindex DEL_SUBNET
@example
message
------------------------------------------------------------------
DEL_EDGE node1 node2
           |     +----> name of destination node
           +----------> name of source node

DEL_SUBNET node 192.168.1.0/24
             |         |     +--> prefixlength
             |         +--------> network address
             +------------------> owner of this subnet
------------------------------------------------------------------
@end example

In case a connection between two daemons is closed or broken, DEL_EDGE messages
are sent to inform the other daemons of that fact. Each daemon will calculate a
new route to the the daemons, or mark them unreachable if there isn't any.

@cindex REQ_KEY
@cindex ANS_KEY
@cindex KEY_CHANGED
@example
message
------------------------------------------------------------------
REQ_KEY origin destination
           |       +--> name of the tinc daemon it wants the key from
           +----------> name of the daemon that wants the key

ANS_KEY origin destination 4ae0b0a82d6e0078 91 64 4
           |       |       \______________/ |  |  +--> MAC length
           |       |               |        |  +-----> digest algorithm
           |       |               |        +--------> cipher algorithm
           |       |               +--> 128 bits key
           |       +--> name of the daemon that wants the key
           +----------> name of the daemon that uses this key

KEY_CHANGED origin
              +--> daemon that has changed it's packet key
------------------------------------------------------------------
@end example

The keys used to encrypt VPN packets are not sent out directly. This is
because it would generate a lot of traffic on VPNs with many daemons, and
chances are that not every tinc daemon will ever send a packet to every
other daemon. Instead, if a daemon needs a key it sends a request for it
via the meta connection of the nearest hop in the direction of the
destination.

@cindex PING
@cindex PONG
@example
daemon  message
------------------------------------------------------------------
origin  PING
dest.   PONG
------------------------------------------------------------------
@end example

There is also a mechanism to check if hosts are still alive. Since network
failures or a crash can cause a daemon to be killed without properly
shutting down the TCP connection, this is necessary to keep an up to date
connection list. PINGs are sent at regular intervals, except when there
is also some other traffic. A little bit of salt (random data) is added
with each PING and PONG message, to make sure that long sequences of PING/PONG
messages without any other traffic won't result in known plaintext.

This basically covers what is sent over the meta connection by tinc.


@c ==================================================================
@node    Security
@section Security

@cindex TINC
@cindex Cabal
Tinc got its name from ``TINC,'' short for @emph{There Is No Cabal}; the
alleged Cabal was/is an organisation that was said to keep an eye on the
entire Internet.  As this is exactly what you @emph{don't} want, we named
the tinc project after TINC.

@cindex SVPN
But in order to be ``immune'' to eavesdropping, you'll have to encrypt
your data. Because tinc is a @emph{Secure} VPN (SVPN) daemon, it does
exactly that: encrypt.
However, encryption in itself does not prevent an attacker from modifying the encrypted data.
Therefore, tinc also authenticates the data.
Finally, tinc uses sequence numbers (which themselves are also authenticated) to prevent an attacker from replaying valid packets.

Since version 1.1pre3, tinc has two protocols used to protect your data; the legacy protocol, and the new Simple Peer-to-Peer Security (SPTPS) protocol.
The SPTPS protocol is designed to address some weaknesses in the legacy protocol.
The new authentication protocol is used when two nodes connect to each other that both have the ExperimentalProtocol option set to yes,
otherwise the legacy protocol will be used.

@menu
* Legacy authentication protocol::
* Simple Peer-to-Peer Security::
* Encryption of network packets::
* Security issues::
@end menu


@c ==================================================================
@node       Legacy authentication protocol
@subsection Legacy authentication protocol

@cindex legacy authentication protocol

@cindex ID
@cindex META_KEY
@cindex CHALLENGE
@cindex CHAL_REPLY
@cindex ACK
@example
daemon  message
--------------------------------------------------------------------------
client  <attempts connection>

server  <accepts connection>

client  ID client 17.2
              |   |  +-> minor protocol version
              |   +----> major protocol version
              +--------> name of tinc daemon

server  ID server 17.2
              |   |  +-> minor protocol version
              |   +----> major protocol version
              +--------> name of tinc daemon

client  META_KEY 94 64 0 0 5f0823a93e35b69e...7086ec7866ce582b
                 |  |  | | \_________________________________/
                 |  |  | |                 +-> RSAKEYLEN bits totally random string S1,
                 |  |  | |                     encrypted with server's public RSA key
                 |  |  | +-> compression level
                 |  |  +---> MAC length
                 |  +------> digest algorithm NID
                 +---------> cipher algorithm NID

server  META_KEY 94 64 0 0 6ab9c1640388f8f0...45d1a07f8a672630
                 |  |  | | \_________________________________/
                 |  |  | |                 +-> RSAKEYLEN bits totally random string S2,
                 |  |  | |                     encrypted with client's public RSA key
                 |  |  | +-> compression level
                 |  |  +---> MAC length
                 |  +------> digest algorithm NID
                 +---------> cipher algorithm NID
--------------------------------------------------------------------------
@end example

The protocol allows each side to specify encryption algorithms and parameters,
but in practice they are always fixed, since older versions of tinc did not
allow them to be different from the default values. The cipher is always
Blowfish in OFB mode, the digest is SHA1, but the MAC length is zero and no
compression is used.

From now on:
@itemize
@item the client will symmetrically encrypt outgoing traffic using S1
@item the server will symmetrically encrypt outgoing traffic using S2
@end itemize

@example
--------------------------------------------------------------------------
client  CHALLENGE da02add1817c1920989ba6ae2a49cecbda0
                  \_________________________________/
                                 +-> CHALLEN bits totally random string H1

server  CHALLENGE 57fb4b2ccd70d6bb35a64c142f47e61d57f
                  \_________________________________/
                                 +-> CHALLEN bits totally random string H2

client  CHAL_REPLY 816a86
                      +-> 160 bits SHA1 of H2

server  CHAL_REPLY 928ffe
                      +-> 160 bits SHA1 of H1

After the correct challenge replies are received, both ends have proved
their identity. Further information is exchanged.

client  ACK 655 123 0
             |   |  +-> options
             |   +----> estimated weight
             +--------> listening port of client

server  ACK 655 321 0
             |   |  +-> options
             |   +----> estimated weight
             +--------> listening port of server
--------------------------------------------------------------------------
@end example

This legacy authentication protocol has several weaknesses, pointed out by security export Peter Gutmann.
First, data is encrypted with RSA without padding.
Padding schemes are designed to prevent attacks when the size of the plaintext is not equal to the size of the RSA key.
Tinc always encrypts random nonces that have the same size as the RSA key, so we do not believe this leads to a break of the security.
There might be timing or other side-channel attacks against RSA encryption and decryption, tinc does not employ any protection against those.
Furthermore, both sides send identical messages to each other, there is no distinction between server and client,
which could make a MITM attack easier.
However, no exploit is known in which a third party who is not already trusted by other nodes in the VPN could gain access.
Finally, the RSA keys are used to directly encrypt the session keys, which means that if the RSA keys are compromised, it is possible to decrypt all previous VPN traffic.
In other words, the legacy protocol does not provide perfect forward secrecy.

@c ==================================================================
@node       Simple Peer-to-Peer Security
@subsection Simple Peer-to-Peer Security
@cindex SPTPS

The SPTPS protocol is designed to address the weaknesses in the legacy protocol.
SPTPS is based on TLS 1.2, but has been simplified: there is no support for exchanging public keys, and there is no cipher suite negotiation.
Instead, SPTPS always uses a very strong cipher suite:
peers authenticate each other using 521 bits ECC keys,
Diffie-Hellman using ephemeral 521 bits ECC keys is used to provide perfect forward secrecy (PFS),
AES-256-CTR is used for encryption, and HMAC-SHA-256 for message authentication.

Similar to TLS, messages are split up in records.
A complete logical record contains the following information:

@itemize
@item uint32_t seqno (network byte order)
@item uint16_t length (network byte order)
@item uint8_t type
@item opaque data[length]
@item opaque hmac[HMAC_SIZE] (HMAC over all preceding fields)
@end itemize

Depending on whether SPTPS records are sent via TCP or UDP, either the seqno or the length field is omitted on the wire
(but they are still included in the calculation of the HMAC);
for TCP packets are guaranteed to arrive in-order so we can infer the seqno, but packets can be split or merged, so we still need the length field to determine the boundaries between records;
for UDP packets we know that there is exactly one record per packet, and we know the length of a packet, but packets can be dropped, duplicated and/or reordered, so we need to include the seqno.

The type field is used to distinguish between application records or handshake records.
Types 0 to 127 are application records, type 128 is a handshake record, and types 129 to 255 are reserved.

Before the initial handshake, no fields are encrypted, and the HMAC field is not present.
After the authentication handshake, the length (if present), type and data fields are encrypted, and the HMAC field is present.
For UDP packets, the seqno field is not encrypted, as it is used to determine the value of the counter used for encryption.

The authentication consists of an exchange of Key EXchange, SIGnature and ACKnowledge messages, transmitted using type 128 records.

Overview:

@example
Initiator   Responder
---------------------
KEX ->
            <- KEX
SIG ->
            <- SIG

...encrypt and HMAC using session keys from now on...

App ->
            <- App
...
            ...

...key renegotiation starts here...

KEX ->
            <- KEX
SIG ->
            <- SIG
ACK ->
            <- ACK

...encrypt and HMAC using new session keys from now on...

App ->
            <- App
...
            ...
---------------------
@end example

Note that the responder does not need to wait before it receives the first KEX message,
it can immediately send its own once it has accepted an incoming connection.

Key EXchange message:

@itemize
@item uint8_t kex_version (always 0 in this version of SPTPS)
@item opaque nonce[32] (random number)
@item opaque ecdh_key[ECDH_SIZE]
@end itemize

SIGnature message:

@itemize
@item opaque ecdsa_signature[ECDSA_SIZE]
@end itemize

ACKnowledge message:

@itemize
@item empty (only sent after key renegotiation)
@end itemize

Remarks:

@itemize
@item At the start, both peers generate a random nonce and an Elliptic Curve public key and send it to the other in the KEX message.
@item After receiving the other's KEX message, both KEX messages are concatenated (see below),
  and the result is signed using ECDSA.
  The result is sent to the other.
@item After receiving the other's SIG message, the signature is verified.
  If it is correct, the shared secret is calculated from the public keys exchanged in the KEX message using the Elliptic Curve Diffie-Helman algorithm.
@item The shared secret key is expanded using a PRF.
  Both nonces and the application specific label are also used as input for the PRF.
@item An ACK message is sent only when doing key renegotiation, and is sent using the old encryption keys.
@item The expanded key is used to key the encryption and HMAC algorithms.
@end itemize

The signature is calculated over this string:

@itemize
@item uint8_t initiator (0 = local peer, 1 = remote peer is initiator)
@item opaque remote_kex_message[1 + 32 + ECDH_SIZE]
@item opaque local_kex_message[1 + 32 + ECDH_SIZE]
@item opaque label[label_length]
@end itemize

The PRF is calculated as follows:

@itemize
@item A HMAC using SHA512 is used, the shared secret is used as the key.
@item For each block of 64 bytes, a HMAC is calculated. For block n: hmac[n] =
  HMAC_SHA512(hmac[n - 1] + seed)
@item For the first block (n = 1), hmac[0] is given by HMAC_SHA512(zeroes + seed),
  where zeroes is a block of 64 zero bytes.
@end itemize

The seed is as follows:

@itemize
@item const char[13] "key expansion"
@item opaque responder_nonce[32]
@item opaque initiator_nonce[32]
@item opaque label[label_length]
@end itemize

The expanded key is used as follows:

@itemize
@item opaque responder_cipher_key[CIPHER_KEYSIZE]
@item opaque responder_digest_key[DIGEST_KEYSIZE]
@item opaque initiator_cipher_key[CIPHER_KEYSIZE]
@item opaque initiator_digest_key[DIGEST_KEYSIZE]
@end itemize

Where initiator_cipher_key is the key used by session initiator to encrypt
messages sent to the responder.

When using 256 bits Ed25519 keys, the AES-256-CTR cipher and HMAC-SHA-256 digest algorithm,
the sizes are as follows:

@example
ECDH_SIZE:       32 (= 256/8)
ECDSA_SIZE:      64 (= 2 * 256/8)
CIPHER_KEYSIZE:  48 (= 256/8 + 128/8)
DIGEST_KEYSIZE:  32 (= 256/8)
@end example

Note that the cipher key also includes the initial value for the counter.

@c ==================================================================
@node       Encryption of network packets
@subsection Encryption of network packets
@cindex encryption

A data packet can only be sent if the encryption key is known to both
parties, and the connection is  activated. If the encryption key is not
known, a request is sent to the destination using the meta connection
to retrieve it.

@cindex UDP
The UDP packets can be either encrypted with the legacy protocol or with SPTPS.
In case of the legacy protocol, the UDP packet containing the network packet from the VPN has the following layout:

@example
... | IP header | UDP header | seqno | VPN packet | MAC | UDP trailer
                             \___________________/\_____/
                                       |             |
                                       V             +---> digest algorithm
                         Encrypted with symmetric cipher
@end example




So, the entire VPN packet is encrypted using a symmetric cipher, including a 32 bits
sequence number that is added in front of the actual VPN packet, to act as a unique
IV for each packet and to prevent replay attacks. A message authentication code
is added to the UDP packet to prevent alteration of packets.
Tinc by default encrypts network packets using Blowfish with 128 bit keys in CBC mode
and uses 4 byte long message authentication codes to make sure
eavesdroppers cannot get and cannot change any information at all from the
packets they can intercept. The encryption algorithm and message authentication
algorithm can be changed in the configuration. The length of the message
authentication codes is also adjustable. The length of the key for the
encryption algorithm is always the default length used by LibreSSL/OpenSSL.

The SPTPS protocol is described in @ref{Simple Peer-to-Peer Security}.
For comparison, this is how SPTPS UDP packets look:

@example
... | IP header | UDP header | seqno | type | VPN packet | MAC | UDP trailer
                                     \__________________/\_____/
                                               |            |
                                               V            +---> digest algorithm
                                 Encrypted with symmetric cipher
@end example

The difference is that the seqno is not encrypted, since the encryption cipher is used in CTR mode,
and therefore the seqno must be known before the packet can be decrypted.
Furthermore, the MAC is never truncated.
The SPTPS protocol always uses the AES-256-CTR cipher and HMAC-SHA-256 digest,
this cannot be changed.


@c ==================================================================
@node    Security issues
@subsection Security issues

In August 2000, we discovered the existence of a security hole in all versions
of tinc up to and including 1.0pre2. This had to do with the way we exchanged
keys. Since then, we have been working on a new authentication scheme to make
tinc as secure as possible. The current version uses the LibreSSL or OpenSSL library and
uses strong authentication with RSA keys.

On the 29th of December 2001, Jerome Etienne posted a security analysis of tinc
1.0pre4. Due to a lack of sequence numbers and a message authentication code
for each packet, an attacker could possibly disrupt certain network services or
launch a denial of service attack by replaying intercepted packets. The current
version adds sequence numbers and message authentication codes to prevent such
attacks.

On the 15th of September 2003, Peter Gutmann posted a security analysis of tinc
1.0.1. He argues that the 32 bit sequence number used by tinc is not a good IV,
that tinc's default length of 4 bytes for the MAC is too short, and he doesn't
like tinc's use of RSA during authentication. We do not know of a security hole
in the legacy protocol of tinc, but it is not as strong as TLS or IPsec.

This version of tinc comes with an improved protocol, called Simple Peer-to-Peer Security,
which aims to be as strong as TLS with one of the strongest cipher suites.

Cryptography is a hard thing to get right. We cannot make any
guarantees. Time, review and feedback are the only things that can
prove the security of any cryptographic product. If you wish to review
tinc or give us feedback, you are stronly encouraged to do so.


@c ==================================================================
@node    Platform specific information
@chapter Platform specific information

@menu
* Interface configuration::
* Routes::
@end menu

@c ==================================================================
@node    Interface configuration
@section Interface configuration

When configuring an interface, one normally assigns it an address and a
netmask.  The address uniquely identifies the host on the network attached to
the interface.  The netmask, combined with the address, forms a subnet.  It is
used to add a route to the routing table instructing the kernel to send all
packets which fall into that subnet to that interface.  Because all packets for
the entire VPN should go to the virtual network interface used by tinc, the
netmask should be such that it encompasses the entire VPN.

For IPv4 addresses:

@multitable {Darwin (MacOS/X)} {ifconfig route add -bla network address netmask netmask prefixlength interface}
@item Linux
@tab @code{ifconfig} @var{interface} @var{address} @code{netmask} @var{netmask}
@item Linux iproute2
@tab @code{ip addr add} @var{address}@code{/}@var{prefixlength} @code{dev} @var{interface}
@item FreeBSD
@tab @code{ifconfig} @var{interface} @var{address} @code{netmask} @var{netmask}
@item OpenBSD
@tab @code{ifconfig} @var{interface} @var{address} @code{netmask} @var{netmask}
@item NetBSD
@tab @code{ifconfig} @var{interface} @var{address} @code{netmask} @var{netmask}
@item Solaris
@tab @code{ifconfig} @var{interface} @var{address} @code{netmask} @var{netmask}
@item Darwin (MacOS/X)
@tab @code{ifconfig} @var{interface} @var{address} @code{netmask} @var{netmask}
@item Windows
@tab @code{netsh interface ip set address} @var{interface} @code{static} @var{address} @var{netmask}
@end multitable

For IPv6 addresses:

@multitable {Darwin (MacOS/X)} {ifconfig route add -bla network address netmask netmask prefixlength interface}
@item Linux
@tab @code{ifconfig} @var{interface} @code{add} @var{address}@code{/}@var{prefixlength}
@item FreeBSD
@tab @code{ifconfig} @var{interface} @code{inet6} @var{address} @code{prefixlen} @var{prefixlength}
@item OpenBSD
@tab @code{ifconfig} @var{interface} @code{inet6} @var{address} @code{prefixlen} @var{prefixlength}
@item NetBSD
@tab @code{ifconfig} @var{interface} @code{inet6} @var{address} @code{prefixlen} @var{prefixlength}
@item Solaris
@tab @code{ifconfig} @var{interface} @code{inet6 plumb up}
@item
@tab @code{ifconfig} @var{interface} @code{inet6 addif} @var{address} @var{address}
@item Darwin (MacOS/X)
@tab @code{ifconfig} @var{interface} @code{inet6} @var{address} @code{prefixlen} @var{prefixlength}
@item Windows
@tab @code{netsh interface ipv6 add address} @var{interface} @code{static} @var{address}/@var{prefixlength}
@end multitable

On some platforms, when running tinc in switch mode, the VPN interface must be set to tap mode with an ifconfig command:

@multitable {Darwin (MacOS/X)} {ifconfig route add -bla network address netmask netmask prefixlength interface}
@item OpenBSD
@tab @code{ifconfig} @var{interface} @code{link0}
@end multitable

On Linux, it is possible to create a persistent tun/tap interface which will
continue to exist even if tinc quit, although this is normally not required.
It can be useful to set up a tun/tap interface owned by a non-root user, so
tinc can be started without needing any root privileges at all.

@multitable {Darwin (MacOS/X)} {ifconfig route add -bla network address netmask netmask prefixlength interface}
@item Linux
@tab @code{ip tuntap add dev} @var{interface} @code{mode} @var{tun|tap} @code{user} @var{username}
@end multitable

@c ==================================================================
@node    Routes
@section Routes

In some cases it might be necessary to add more routes to the virtual network
interface.  There are two ways to indicate which interface a packet should go
to, one is to use the name of the interface itself, another way is to specify
the (local) address that is assigned to that interface (@var{local_address}). The
former way is unambiguous and therefore preferable, but not all platforms
support this.

Adding routes to IPv4 subnets:

@multitable {Darwin (MacOS/X)} {ifconfig route add -bla network address netmask netmask prefixlength interface}
@item Linux
@tab @code{route add -net} @var{network_address} @code{netmask} @var{netmask} @var{interface}
@item Linux iproute2
@tab @code{ip route add} @var{network_address}@code{/}@var{prefixlength} @code{dev} @var{interface}
@item FreeBSD
@tab @code{route add} @var{network_address}@code{/}@var{prefixlength} @var{local_address}
@item OpenBSD
@tab @code{route add} @var{network_address}@code{/}@var{prefixlength} @var{local_address}
@item NetBSD
@tab @code{route add} @var{network_address}@code{/}@var{prefixlength} @var{local_address}
@item Solaris
@tab @code{route add} @var{network_address}@code{/}@var{prefixlength} @var{local_address} @code{-interface}
@item Darwin (MacOS/X)
@tab @code{route add} @var{network_address}@code{/}@var{prefixlength} @var{local_address}
@item Windows
@tab @code{netsh routing ip add persistentroute} @var{network_address} @var{netmask} @var{interface} @var{local_address}
@end multitable

Adding routes to IPv6 subnets:

@multitable {Darwin (MacOS/X)} {ifconfig route add -bla network address netmask netmask prefixlength interface}
@item Linux
@tab @code{route add -A inet6} @var{network_address}@code{/}@var{prefixlength} @var{interface}
@item Linux iproute2
@tab @code{ip route add} @var{network_address}@code{/}@var{prefixlength} @code{dev} @var{interface}
@item FreeBSD
@tab @code{route add -inet6} @var{network_address}@code{/}@var{prefixlength} @var{local_address}
@item OpenBSD
@tab @code{route add -inet6} @var{network_address} @var{local_address} @code{-prefixlen} @var{prefixlength}
@item NetBSD
@tab @code{route add -inet6} @var{network_address} @var{local_address} @code{-prefixlen} @var{prefixlength}
@item Solaris
@tab @code{route add -inet6} @var{network_address}@code{/}@var{prefixlength} @var{local_address} @code{-interface}
@item Darwin (MacOS/X)
@tab ?
@item Windows
@tab @code{netsh interface ipv6 add route} @var{network address}/@var{prefixlength} @var{interface}
@end multitable


@c ==================================================================
@node    About us
@chapter About us


@menu
* Contact information::
* Authors::
@end menu


@c ==================================================================
@node    Contact information
@section Contact information

@cindex website
Tinc's website is at @url{https://www.tinc-vpn.org/},
this server is located in the Netherlands.

@cindex IRC
We have an IRC channel on the FreeNode and OFTC IRC networks. Connect to
@uref{https://freenode.net/, irc.freenode.net}
or
@uref{https://www.oftc.net/, irc.oftc.net}
and join channel #tinc.


@c ==================================================================
@node    Authors
@section Authors

@table @asis
@item Ivo Timmermans (zarq)
@item Guus Sliepen (guus) (@email{guus@@tinc-vpn.org})
@end table

We have received a lot of valuable input from users.  With their help,
tinc has become the flexible and robust tool that it is today.  We have
composed a list of contributions, in the file called @file{THANKS} in
the source distribution.


@c ==================================================================
@node    Concept Index
@unnumbered Concept Index

@c ==================================================================
@printindex cp


@c ==================================================================
@contents
@bye