Releasing 1.0.24.

[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{} 1998-2014 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

@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{} 1998-2014 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::
* 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{http://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

For OpenBSD version 2.9 and higher,
the tun driver is included in the default kernel configuration.
There is also a kernel patch from @uref{http://diehard.n-r-g.com/stuff/openbsd/}
which adds a tap device to OpenBSD which should work with tinc,
but with recent versions of OpenBSD,
a tun device can act as a tap device by setting the link0 option with ifconfig.


@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{http://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.
Tinc supports either the driver from @uref{http://tuntaposx.sourceforge.net/},
which supports both tun and tap style devices,
and also the driver from from @uref{http://chrisp.de/en/projects/tunnel.html}.
The former driver is recommended.
The tunnel driver must be loaded before starting tinc with the following command:

@example
kmodload tunnel
@end example


@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{http://openvpn.sourceforge.net}.
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 OpenSSL,
zlib and lzo 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
* OpenSSL::
* zlib::
* lzo::
@end menu


@c ==================================================================
@node       OpenSSL
@subsection OpenSSL

@cindex OpenSSL
For all cryptography-related functions, tinc uses the functions provided
by 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 you have to install OpenSSL manually, you can get the source code
from @url{http://www.openssl.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 OpenSSL libraries from source, it may be necessary
to let configure know where they are, by passing configure one of the
--with-openssl-* parameters.

@example
--with-openssl=DIR      OpenSSL library and headers prefix
--with-openssl-include=DIR OpenSSL headers directory
                        (Default is OPENSSL_DIR/include)
--with-openssl-lib=DIR  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{http://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
(http://www.tinc-vpn.org/) to link the LZO library with the OpenSSL library
(http://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.gzip.org/zlib/}.  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{http://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
@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{http://www.tinc-vpn.org/download/, download page}, which has
the checksums of these files listed; you may wish to check these with
md5sum before continuing.

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 the MacOS/X Developer Tools
from @uref{http://developer.apple.com/tools/macosxtools.html} and
a recent version of Fink from @uref{http://www.finkproject.org/}.

After installation use fink to download and install the following packages:
autoconf25, automake, dlcompat, m4, openssl, zlib and lzo.

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

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

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::
* Generating keypairs::
* 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, generate the configuration files (@file{tinc.conf}, your host configuration file, @file{tinc-up} and perhaps @file{tinc-down}).
Then generate the keypairs.
Finally, distribute the host configuration files.
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 sites 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 tincd with the -n argument,
which will assign a netname to this daemon.

The effect of this is that the daemon will set its configuration
root to @file{@value{sysconfdir}/tinc/@var{netname}/}, where @var{netname} is your argument to the -n
option.  You'll notice that it appears in syslog as @file{tinc.@var{netname}}.

However, it is not strictly necessary that you call tinc with the -n
option.  In this case, the network name would just be empty, and it will
be used as such.  tinc now looks for files in @file{@value{sysconfdir}/tinc/}, instead of
@file{@value{sysconfdir}/tinc/@var{netname}/}; the configuration file should be @file{@value{sysconfdir}/tinc/tinc.conf},
and the host configuration files are now expected to be in @file{@value{sysconfdir}/tinc/hosts/}.

But it is highly recommended that you use this feature of tinc, because
it will be so much clearer whom your daemon talks to.  Hence, we will
assume that you use it.


@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.


@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.

In this section 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 BindToAddress
@item BindToAddress = <@var{address}> [<@var{port}>] [experimental]
If your computer has more than one IPv4 or IPv6 address, tinc
will by default listen on all of them for incoming connections.
Multiple BindToAddress variables may be specified,
in which case listening sockets for each specified address are made.

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

This option may not work on all platforms.

@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.

@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 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,
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 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 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.

@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 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 GraphDumpFile
@item GraphDumpFile = <@var{filename}> [experimental]
If this option is present,
tinc will dump the current network graph to the file @var{filename}
every minute, unless there were no changes to the graph.
The file is in a format that can be read by graphviz tools.
If @var{filename} starts with a pipe symbol |,
then the rest of the filename is interpreted as a shell command
that is executed, the graph is then sent to stdin.

@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 IffOneQueue
@item IffOneQueue = <yes|no> (no) [experimental]
(Linux only) Set IFF_ONE_QUEUE flag on TUN/TAP devices.

@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 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 LocalDiscovery
@item LocalDiscovery = <yes | no> (no) [experimental]
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 broadcast packets to the LAN during path MTU discovery.
This feature may not work in all possible situations.

@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 MaxTimeout
@item MaxTimeout = <@var{seconds}> (900)
This is the maximum delay before trying to reconnect to other tinc daemons.

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

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 gethostnname() 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{tincd --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> (16)
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 16 will track up to 128 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 UDPRcvBuf
@item UDPRcvBuf = <bytes> (OS default)
Sets the socket receive buffer size for the UDP socket, in bytes.
If unset, the default buffer size will be used by the operating system.

@cindex UDPSndBuf
@item UDPSndBuf = <bytes> Pq OS default
Sets the socket send buffer size for the UDP socket, in bytes.
If unset, the default buffer size will be used by the operating system.

@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.
Any cipher supported by OpenSSL is recognized.
Furthermore, specifying "none" will turn off packet encryption.
It is best to use only those ciphers which support CBC mode.

@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.
Any digest supported by OpenSSL is recognized.
Furthermore, specifying "none" will turn off packet authentication.

@cindex IndirectData
@item IndirectData = <yes|no> (no)
This option specifies whether other tinc daemons besides the one you
specified with ConnectTo can make a direct connection to you.  This is
especially useful if you are behind a firewall and it is impossible to
make a connection from the outside to your tinc daemon.  Otherwise, 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.
Can be anything from 0
up to the length of the digest produced by the digest algorithm.

@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 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{tincd --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{http://www.ietf.org/rfc/rfc1519.txt, RFC1519}

@cindex Subnet weight
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) [deprecated]
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.

Since version 1.0.10, tinc will automatically detect whether communication via
UDP is possible or not.
@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.
Under Windows (not Cygwin), the scripts should have the extension .bat.

@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.
@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} 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.

@end table


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

@subsubheading Step 1.  Creating the main configuration file

The main configuration file will be called @file{@value{sysconfdir}/tinc/@var{netname}/tinc.conf}.
Adapt the following example to create a basic configuration file:

@example
Name = @var{yourname}
Device = @file{/dev/tap0}
@end example

Then, if you know to which other tinc daemon(s) yours is going to connect,
add `ConnectTo' values.

@subsubheading Step 2.  Creating your host configuration file

If you added a line containing `Name = yourname' in the main configuarion file,
you will need to create a host configuration file @file{@value{sysconfdir}/tinc/@var{netname}/hosts/yourname}.
Adapt the following example to create a host configuration file:

@example
Address = your.real.hostname.org
Subnet = 192.168.1.0/24
@end example

You can also use an IP address instead of a hostname.
The `Subnet' specifies the address range that is local for @emph{your part of the VPN only}.
If you have multiple address ranges you can specify more than one `Subnet'.
You might also need to add a `Port' if you want your tinc daemon to run on a different port number than the default (655).


@c ==================================================================
@node    Generating keypairs
@section Generating keypairs

@cindex key generation
Now that you have already created the main configuration file and your host configuration file,
you can easily create a public/private keypair by entering the following command:

@example
tincd -n @var{netname} -K
@end example

Tinc will generate a public and a private key and ask you where to put them.
Just press enter to accept the defaults.


@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.

An example @file{tinc-up} script:

@example
#!/bin/sh
ifconfig $INTERFACE 192.168.1.1 netmask 255.255.0.0
@end example

This script gives the interface an IP address and a netmask.
The kernel will also automatically add a 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 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.

@subsubheading For Branch A

@emph{BranchA} would be configured like this:

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

@example
# 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
Device = /dev/tap0
@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 tap0 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 tap 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
# 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 tap0 device.  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
# 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
Device = /dev/tap1
@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
# 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
Device = /dev/net/tun
@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.
Also note that since D uses the tun/tap driver, the network interface
will not be called `tun' or `tap0' or something like that, but will
have the same name as netname.

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 generated a public/private keypair with the following command:

@example
tincd -n company -K
@end example

The private key is stored in @file{@value{sysconfdir}/tinc/company/rsa_key.priv},
the public key is put into the host configuration file in the @file{@value{sysconfdir}/tinc/company/hosts/} directory.
During key generation, tinc automatically guesses the right filenames based on the -n option and
the Name directive in the @file{tinc.conf} file (if it is available).

@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
tincd -n @var{netname}
@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 -k, --kill[=@var{signal}]
Attempt to kill a running tincd (optionally with the specified @var{signal} instead of SIGTERM) and exit.
Use it in conjunction with the -n option to make sure you kill the right tinc daemon.
Under native Windows the optional argument is ignored,
the service will always be stopped and removed.

@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 -K, --generate-keys[=@var{bits}]
Generate public/private keypair of @var{bits} length. If @var{bits} is not specified,
2048 is the default. 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
in combination with -K). After that, tinc will quit.

@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.

@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 --pidfile=@var{file}
Write PID to @var{file} instead of @file{@value{localstatedir}/run/tinc.@var{netname}.pid}.

@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.

@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.

@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.

@item INT
Temporarily increases debug level to 5.
Send this signal again to revert to the original level.

@item USR1
Dumps the connection list to syslog.

@item USR2
Dumps virtual network device statistics, all known nodes, edges and subnets to syslog.

@item WINCH
Purges all information remembered about unreachable nodes.

@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. Since version 1.0.10, tinc will automatically fall back to TCP if direct communication via UDP is not possible.

@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.
@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    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{Authentication protocol}. 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.
Tinc by default uses blowfish encryption with 128 bit keys in CBC mode, 32 bit
sequence numbers and 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 OpenSSL.

@menu
* Authentication protocol::
* Encryption of network packets::
* Security issues::
@end menu


@c ==================================================================
@node       Authentication protocol
@subsection Authentication protocol

@cindex authentication
A new scheme for authentication in tinc has been devised, which offers some
improvements over the protocol used in 1.0pre2 and 1.0pre3. Explanation is
below.

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

server  <accepts connection>

client  ID client 12
              |   +---> version
              +-------> name of tinc daemon

server  ID server 12
              |   +---> version
              +-------> name of tinc daemon

client  META_KEY 5f0823a93e35b69e...7086ec7866ce582b
                 \_________________________________/
                                 +-> RSAKEYLEN bits totally random string S1,
                                     encrypted with server's public RSA key

server  META_KEY 6ab9c1640388f8f0...45d1a07f8a672630
                 \_________________________________/
                                 +-> RSAKEYLEN bits totally random string S2,
                                     encrypted with client's public RSA key

From now on:
 - the client will symmetrically encrypt outgoing traffic using S1
 - the server will symmetrically encrypt outgoing traffic using S2

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 new scheme has several improvements, both in efficiency and security.

First of all, the server sends exactly the same kind of messages over the wire
as the client. The previous versions of tinc first authenticated the client,
and then the server. This scheme even allows both sides to send their messages
simultaneously, there is no need to wait for the other to send something first.
This means that any calculations that need to be done upon sending or receiving
a message can also be done in parallel. This is especially important when doing
RSA encryption/decryption. Given that these calculations are the main part of
the CPU time spent for the authentication, speed is improved by a factor 2.

Second, only one RSA encrypted message is sent instead of two. This reduces the
amount of information attackers can see (and thus use for a cryptographic
attack). It also improves speed by a factor two, making the total speedup a
factor 4.

Third, and most important:
The symmetric cipher keys are exchanged first, the challenge is done
afterwards. In the previous authentication scheme, because a man-in-the-middle
could pass the challenge/chal_reply phase (by just copying the messages between
the two real tinc daemons), but no information was exchanged that was really
needed to read the rest of the messages, the challenge/chal_reply phase was of
no real use. The man-in-the-middle was only stopped by the fact that only after
the ACK messages were encrypted with the symmetric cipher. Potentially, it
could even send it's own symmetric key to the server (if it knew the server's
public key) and read some of the metadata the server would send it (it was
impossible for the mitm to read actual network packets though). The new scheme
however prevents this.

This new scheme makes sure that first of all, symmetric keys are exchanged. The
rest of the messages are then encrypted with the symmetric cipher. Then, each
side can only read received messages if they have their private key. The
challenge is there to let the other side know that the private key is really
known, because a challenge reply can only be sent back if the challenge is
decrypted correctly, and that can only be done with knowledge of the private
key.

Fourth: the first thing that is sent via the symmetric cipher encrypted
connection is a totally random string, so that there is no known plaintext (for
an attacker) in the beginning of the encrypted stream.


@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. The packet is stored in a queue while waiting for the
key to arrive.

@cindex UDP
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. By default the
first 4 bytes of the digest are used for this, but this can be changed using
the MACLength configuration variable.

@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 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 this version of tinc, but tinc's security is not as strong as TLS or IPsec.
We will address these issues in tinc 2.0.

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{http://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{http://www.freenode.net/, irc.freenode.net}
or
@uref{http://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