Fix bug when dropping an old connection in favour of a new one from the

[meshlink] / doc / tinc.texi

\input texinfo   @c -*-texinfo-*-
@c $Id: tinc.texi,v 1.8.4.18 2001/05/25 12:45:37 guus Exp $
@c %**start of header
@setfilename tinc.info
@settitle tinc Manual
@setchapternewpage odd
@c %**end of header

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

This is the info manual for tinc, a Virtual Private Network daemon.

Copyright @copyright{} 1998-2001 Ivo Timmermans
<itimmermans@@bigfoot.com>, Guus Sliepen <guus@@sliepen.warande.net> and
Wessel Dankers <wsl@@nl.linux.org>.

$Id: tinc.texi,v 1.8.4.18 2001/05/25 12:45:37 guus Exp $

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
@cindex copyright
Copyright @copyright{} 1998-2001 Ivo Timmermans
<itimmermans@@bigfoot.com>, Guus Sliepen <guus@@sliepen.warande.net> and
Wessel Dankers <wsl@@nl.linux.org>.

$Id: tinc.texi,v 1.8.4.18 2001/05/25 12:45:37 guus Exp $

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

@c ==================================================================
@node Top, Introduction, (dir), (dir)

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


@contents

@c ==================================================================
@node    Introduction, Preparations, Top, Top
@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
* VPNs::                        Virtual Private Networks in general
* tinc::                        about tinc
* Supported platforms::
@end menu

@c ==================================================================
@node    VPNs, tinc, Introduction, Introduction
@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 singe 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, Supported platforms, VPNs, Introduction
@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 @samp{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,  , tinc, Introduction
@section Supported platforms

@cindex platforms
tinc has been verified to work under Linux, FreeBSD and Solaris, with
various hardware architectures.  These are the three platforms
that are supported by the universial TUN/TAP device driver, so if
support for other operating systems is added to this driver, perhaps
tinc will run on them as well.  Without this driver, tinc will most
likely compile and run, but it will not be able to send or receive data
packets.

@cindex release
The official release only truly supports Linux.
For an up to date list of supported platforms, please check the list on
our website:
@uref{http://tinc.nl.linux.org/platforms.html}.


@c ==================================================================
@subsection Linux

@cindex Linux
tinc was first written for Linux running on an intel x86 processor, so
this is the best supported platform.  The protocol however, and actually
anything about tinc, has been rewritten to support random byte ordering
and arbitrary word length.  So in theory it should run on other
processors that Linux runs on.  It has already been verified to run on
alpha and sparc processors as well.

tinc uses the ethertap device or the universal TUN/TAP driver. The former is provided in the standard kernel
from version 2.1.60 up to 2.3.x, but has been replaced in favour of the TUN/TAP driver in kernel versions 2.4.0 and later.


@c ==================================================================
@subsection FreeBSD

@cindex FreeBSD
tinc on FreeBSD relies on the universial TUN/TAP driver for its data
acquisition from the kernel.  Therefore, tinc will work on the same platforms
as this driver.  These are: FreeBSD 3.x, 4.x, 5.x.


@c ==================================================================
@subsection Solaris

@cindex Solaris
tinc on Solaris relies on the universial TUN/TAP driver for its data
acquisition from the kernel.  Therefore, tinc will work on the same platforms
as this driver.  These are: Solaris, 2.1.x.


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

@c ==================================================================
@node    Preparations, Installation, Introduction, Top
@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, Libraries, Preparations, Preparations
@section Configuring the kernel

@cindex RedHat
@cindex Debian
@cindex netlink_dev
@cindex tun
@cindex ethertap
If you are running Linux, chances are good that your kernel already supports
all the devices that tinc needs for proper operation.  For example, the
standard kernel from Redhat Linux already has support for ethertap and netlink
compiled in.  Debian users can use the modconf utility to select the modules.
If your Linux distribution supports this method of selecting devices, look out
for something called `ethertap', and `netlink_dev' if it is using a kernel
version prior to 2.4.0. In that case you will need both these devices.  If you
are using kernel 2.4.0 or later, you need to select `tun'.

@cindex Kernel-HOWTO
If you can install these devices in a similar manner, you may skip this section.
Otherwise, you will have to recompile the kernel in order to turn on the required features.
If you are unfamiliar with the process of configuring and compiling a new kernel,
you should read the @uref{http://howto.linuxberg.com/LDP/HOWTO/Kernel-HOWTO.html, Kernel HOWTO} first.

@menu
* Configuration of Linux kernels 2.1.60 up to 2.4.0::
* Configuration of Linux kernels 2.4.0 and higher::
* Configuration of FreeBSD kernels::
* Configuration of Solaris kernels::
@end menu


@c ==================================================================
@node       Configuration of Linux kernels 2.1.60 up to 2.4.0, Configuration of Linux kernels 2.4.0 and higher, Configuring the kernel, Configuring the kernel
@subsection Configuration of Linux kernels 2.1.60 up to 2.4.0

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
Networking options
[*] Kernel/User netlink socket
<M> Netlink device emulation
Network device support
<M> Ethertap network tap
@end example

If you want to run more than one instance of tinc or other programs that use
the ethertap, you have to compile the ethertap driver as a module, otherwise
you can also choose to compile it directly into the kernel.

If you decide to build any of these as dynamic kernel modules, it's a good idea
to add these lines to @file{/etc/modules.conf}:

@example
alias char-major-36 netlink_dev
alias tap0 ethertap
options tap0 -o tap0 unit=0
alias tap1 ethertap
options tap1 -o tap1 unit=1
...
alias tap@emph{N} ethertap
options tap@emph{N} -o tap@emph{N} unit=@emph{N}
@end example

Add as much alias/options lines as necessary.


@c ==================================================================
@node       Configuration of Linux kernels 2.4.0 and higher, Configuration of FreeBSD kernels, Configuration of Linux kernels 2.1.60 up to 2.4.0, Configuring the kernel
@subsection Configuration of Linux kernels 2.4.0 and higher

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 have an early 2.4 kernel, you can choose both the TUN/TAP driver and the
`Ethertap network tap' device.  This latter is marked obsolete, and chances are
that it won't even function correctly anymore.  Make sure you select the
universal TUN/TAP driver.

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, Configuration of Solaris kernels, Configuration of Linux kernels 2.4.0 and higher, Configuring the kernel
@subsection Configuration of FreeBSD kernels

This section will contain information on how to configure your FreeBSD
kernel to support the universal TUN/TAP device.  For 5.0 and 4.1
systems, this is included in the kernel configuration, for earlier
systems (4.0 and 3.x), you need to install the universal TUN/TAP driver
yourself.

Unfortunately somebody still has to write the text.


@c ==================================================================
@node       Configuration of Solaris kernels,  , Configuration of FreeBSD kernels, Configuring the kernel
@subsection Configuration of Solaris kernels

This section will contain information on how to configure your Solaris
kernel to support the universal TUN/TAP device.  You need to install
this driver yourself.

Unfortunately somebody still has to write the text.


@c ==================================================================
@node    Libraries,  , Configuring the kernel, Preparations
@section Libraries

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

@menu
* OpenSSL::
@end menu


@c ==================================================================
@node       OpenSSL,  , Libraries, Libraries
@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 without having OpenSSL
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
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}, therefore we
include an addition to the GPL (see also the file COPYING.README):

@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


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

@c ==================================================================
@node    Installation, Configuration, Preparations, Top
@chapter Installation

If you use Redhat or 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 don't run either of these systems, 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://tinc.nl.linux.org/download.html, 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, System files, Installation, Installation
@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.


@c ==================================================================
@node    System files,  , Building and installing tinc, Installation
@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, Other files, System files, System files
@subsection Device files

@cindex device files
First, you'll need the special device file(s) that form the interface
between the kernel and the daemon.

The permissions for these files have to be such that only the super user
may read/write to this file.  You'd want this, because otherwise
eavesdropping would become a bit too easy.  This does, however, imply
that you'd have to run tincd as root.

If you use Linux and have a kernel version prior to 2.4.0, you have to make the
ethertap devices:

@example
mknod -m 600 /dev/tap0 c 36 16
chown 0.0 /dev/tap0
mknod -m 600 /dev/tap1 c 36 17
chown 0.0 /dev/tap0
...
mknod -m 600 /dev/tap@emph{N} c 36 @emph{N+16}
chown 0.0 /dev/tap@emph{N}
@end example

There is a maximum of 16 ethertap devices.

If you use the universal TUN/TAP driver, you have to create the
following device file (unless it already exist):

@example
mknod -m 600 /dev/tun c 10 200
chown 0.0 /dev/tun
@end example

If you use Linux, and you run the new 2.4 kernel using the devfs filesystem,
then the TUN/TAP device will probably be automatically generated as
@file{/dev/net/tun}.

Unlike the ethertap device, you do not need multiple device files if
you are planning to run multiple tinc daemons.


@c ==================================================================
@node       Other files,  , Device files, System 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 <itimmermans@@bigfoot.com>
@end example


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


@c ==================================================================
@node    Configuration, Running tinc, Installation, Top
@chapter Configuration

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

@c ==================================================================
@node    Configuration introduction, Multiple networks, Configuration, Configuration
@section Configuration introduction

@cindex Network Administrators Guide
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?
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.
A good resource on networking is the
@uref{http://www.linuxdoc.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 (tinc.conf, your host configuration file, tinc-up and perhaps tinc-down).
Then generate the keypairs.
Finally, distribute the host configuration files.
These steps are described in the subsections below.


@c ==================================================================
@node    Multiple networks, How connections work, Configuration introduction, Configuration
@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 ``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 /etc/tinc/netname/, where netname is your argument to the -n
option.  You'll notice that it appears in syslog as ``tinc.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 /etc/tinc/, instead of
/etc/tinc/netname/; the configuration file should be /etc/tinc/tinc.conf,
and the host configuration files are now expected to be in /etc/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, Configuration files, Multiple networks, Configuration
@section How connections work

When tinc starts up, it parses the command-line options and then
reads in the configuration file.
If it sees a `ConnectTo' value pointing to another tinc daemon in the file,
it will try to connect to that other one.
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 any 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 eachother however.


@c ==================================================================
@node    Configuration files, Generating keypairs, How connections work, Configuration
@section Configuration files

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

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.

In this section all valid variables are listed in alphabetical order.
The default value is given between parentheses,
other comments are between square brackets and
required directives are given in @strong{bold}.

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


@c ==================================================================
@node    Main configuration variables, Host configuration variables, Configuration files, Configuration files
@subsection Main configuration variables

@table @asis
@item @strong{ConnectTo = <name>}
@cindex ConnectTo
Specifies which host to connect to on startup.  Multiple ConnectTo
variables may be specified, if connecting to the first one fails then
tinc will try the next one, and so on.  It is possible to specify
hostnames for dynamic IP addresses (like those given on dyndns.org),
tinc will not cache the resolved IP address.

If you don't specify a host with ConnectTo, regardless of whether a
value for ConnectPort is given, tinc won't connect at all, and will
instead just listen for incoming connections.

@item Hostnames = <yes|no> (no)
@cindex Hostnames
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.

@item Interface = <device>
@cindex Interface
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.

@item InterfaceIP = <local address>
@cindex InterfaceIP
If your computer has more than one IP address on a single interface (for
example if you are running virtual hosts), tinc will by default listen
on all of them for incoming connections.  It is possible to bind tinc to
a single IP address with this variable.  It is still possible to listen
on several interfaces at the same time though, if they share the same IP
address.

@item KeyExpire = <seconds> (3600)
@cindex KeyExpire
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.

@item @strong{Name = <name>}
@cindex Name
This is a symbolic name for this connection.  It can be anything

@item PingTimeout = <seconds> (60)
@cindex PingTimeout
The number of seconds of inactivity that tinc will wait before sending a
probe to the other end.  If that other end doesn't answer within that
same amount of seconds, the connection is terminated, and the others
will be notified of this.

@item PrivateKey = <key> [obsolete]
@cindex PrivateKey
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.

@item @strong{PrivateKeyFile = <path>} [recommended]
@cindex PrivateKeyFile
This is the full path name of the RSA private key file that was
generated by ``tincd --generate-keys''.  It must be a full path, not a
relative directory.

@item @strong{TapDevice = <device>} (/dev/tap0 or /dev/net/tun)
@cindex TapDevice
The ethertap device to use.  Note that you can only use one device per
daemon.  The info pages of the tinc package contain more information
about configuring an ethertap device for Linux.

@end table


@c ==================================================================
@node    Host configuration variables, How to configure, Main configuration variables, Configuration files
@subsection Host configuration variables

@table @asis
@item @strong{Address = <IP address|hostname>} [recommended]
@cindex Address
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.

@item IndirectData = <yes|no> (no) [experimental]
@cindex IndirectData
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.

@item Port = <port> (655)
@cindex Port
Connect to the upstream host (given with the ConnectTo directive) on
port port.  port may be given in decimal (default), octal (when preceded
by a single zero) o hexadecimal (prefixed with 0x).  port is the port
number for both the UDP and the TCP (meta) connections.

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

@item PublicKeyFile = <path> [obsolete]
@cindex PublicKeyFile
This is the full path name of the RSA public key file that was generated
by ``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.

@item Subnet = <IP address/maskbits>
@cindex Subnet
This is the subnet range of all IP addresses that will be accepted by
the host that defines it.

The range must be contained in the IP address range of the tap device,
not the real IP address of the host running tincd.

@cindex CIDR notation
maskbits 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{ftp://ftp.isi.edu/in-notes/rfc1519.txt, RFC1519}

@item TCPonly = <yes|no> (no) [experimental]
@cindex TCPonly
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. This is
experimental code, try this at your own risk. It may not work at all.
Setting this options also implicitly sets IndirectData.
@end table


@c ==================================================================
@node    How to configure,  , Host configuration variables, Configuration files
@subsection How to configure

@subsubheading Step 1.  Creating the main configuration file

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

@example
Name = @emph{yourname}
TapDevice = @emph{/dev/tap0}
PrivateKeyFile = /etc/tinc/@emph{netname}/rsa_key.priv
@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{/etc/tinc/netname/hosts/yourname}.
Adapt the following example to create a host configuration file:

@example
Address = @emph{your.real.hostname.org}
Subnet = @emph{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, Network interfaces, Configuration files, Configuration
@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 @emph{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, Example configuration, Generating keypairs, Configuration
@section Network interfaces

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

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

tinc will open an ethertap device or TUN/TAP device, which will also
create a network interface called `tap0', or `tap1', and so on if you are using
the ethertap driver, or a network interface with the same name as netname
if you are using the universal TUN/TAP driver.

@cindex tinc-up
You can configure that device by putting ordinary ifconfig, route, and other commands
to a script named @file{/etc/tinc/netname/tinc-up}. When tinc starts, this script
will be executed. When tinc exits, it will execute the script named
@file{/etc/tinc/netname/tinc-down}, but normally you don't need to create that script.

An example @file{tinc-up} script when using the TUN/TAP driver:

@example
#!/bin/sh
ifconfig $NETNAME hw ether fe:fd:00:00:00:00
ifconfig $NETNAME @emph{xx}.@emph{xx}.@emph{xx}.@emph{xx} netmask @emph{mask}
ifconfig $NETNAME -arp
@end example

@cindex MAC address
@cindex hardware address
The first line sets up the MAC address of the network interface.
Due to the nature of how Ethernet and tinc work, it has to be set to fe:fd:00:00:00:00.
(tinc versions prior to 1.0pre3 required that the MAC address matched the IP address.)
You can use the environment variable $NETNAME to get the name of the interface.
If you are using the ethertap driver however, you need to replace it with tap@emph{N},
corresponding to the device file name.

@cindex ifconfig
The next line 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.

@cindex arp
The last line tells the kernel not to use ARP on that interface.
Again this has to do with how Ethernet and tinc work. Don't forget to add this line.


@c ==================================================================
@node    Example configuration,  , Network interfaces, 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

``gateway'' is the VPN IP address of the machine that is running the
tincd.  ``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&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{/etc/tinc/company/tinc-up}:

@example
# Real interface of internal network:
# ifconfig eth0 10.1.54.1 netmask 255.255.0.0 broadcast 10.1.255.255

ifconfig tap0 hw ether fe:fd:00:00:00:00
ifconfig tap0 10.1.54.1 netmask 255.0.0.0
ifconfig tap0 -arp
@end example

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

@example
Name = BranchA
PrivateKey = /etc/tinc/company/rsa_key.priv
TapDevice = /dev/tap0
@end example

On all hosts, /etc/tinc/company/hosts/BranchA contains:

@example
Subnet = 10.1.0.0/16
Address = 1.2.3.4

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 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.

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


@subsubheading For Branch B

In @file{/etc/tinc/company/tinc-up}:

@example
# Real interface of internal network:
# ifconfig eth0 10.2.43.8 netmask 255.255.0.0 broadcast 10.2.255.255

ifconfig tap0 hw ether fe:fd:00:00:00:00
ifconfig tap0 10.2.1.12 netmask 255.0.0.0
ifconfig tap0 -arp
@end example

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

@example
Name = BranchB
ConnectTo = BranchA
PrivateKey = /etc/tinc/company/rsa_key.priv
@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 no-one can
connect to this node.

On all hosts, in @file{/etc/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{/etc/tinc/company/tinc-up}:

@example
# Real interface of internal network:
# ifconfig eth0 10.3.69.254 netmask 255.255.0.0 broadcast 10.3.255.255

ifconfig tap1 hw ether fe:fd:00:00:00:00
ifconfig tap1 10.3.69.254 netmask 255.0.0.0
ifconfig tap1 -arp
@end example

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

@example
Name = BranchC
ConnectTo = BranchA
TapDevice = /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{/etc/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{/etc/tinc/company/tinc-up}:

@example
# Real interface of internal network:
# ifconfig eth0 10.4.3.32 netmask 255.255.0.0 broadcast 10.4.255.255

ifconfig company hw ether fe:fd:0a:04:03:20
ifconfig company 10.4.3.32 netmask 255.0.0.0
ifconfig company -arp
@end example

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

@example
Name = BranchD
ConnectTo = BranchC
TapDevice = /dev/net/tun
PrivateKeyFile = /etc/tinc/company/rsa_key.priv
@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{/etc/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{/etc/tinc/company/rsa_key.priv},
the public key is put into the host configuration file in the @file{/etc/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, Technical information, Configuration, Top
@chapter Running tinc

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

@example
tincd -n @emph{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::
* Error messages::
@end menu


@c ==================================================================
@node    Runtime options, Error messages,  , Running tinc
@section Runtime options

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

This list is a longer version of that in the manpage.  The latter is
generated automatically, so may be more up-to-date.

@cindex command line
@cindex runtime options
@cindex options
@c from the manpage
@table @samp
@item -c, --config=PATH
Read configuration options from the directory PATH.  The default is
@file{/etc/tinc/netname/}.

@cindex debug level
@item -d
Increase debug level.  The higher it gets, the more gets
logged.  Everything goes via syslog.

0 is the default, only some basic information connection attempts get
logged.  Setting it to 1 will log a bit more, still not very
disturbing.  With two -d's tincd will log protocol information, which can
get pretty noisy.  Three or more -d's will output every single packet
that goes out or comes in, which probably generates more data than the
packets themselves.

@item -k, --kill
Attempt to kill a running tincd and exit.  A TERM signal (15) gets sent
to the daemon that his its PID in /var/run/tinc.pid.

Because it kills only one tinc daemon, you should use -n here if you
started it that way.  It will then read the PID from
@file{/var/run/tinc.NETNAME.pid}.

@item -n, --net=NETNAME
Connect to net NETNAME.  @xref{Multiple networks}.

@item -K, --generate-keys[=BITS]
Generate public/private keypair of BITS length. If BITS is not specified,
1024 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 --help
Display a short reminder of these runtime options and terminate.

@item --version
Output version information and exit.

@end table


@c ==================================================================
@node    Error messages,  , Runtime options, Running tinc
@section Error messages

What follows is a list of the most common error messages you can see
when configuring tinc.  Most of these messages are visible in the syslog
only, so keep an eye on it!

@table @strong
@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.
@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
tap 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 netmask which is
just as large as the netmask of the tap device. 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 `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 Network doesn't work, syslog shows only packets of length 46

@cindex arp
@example
Jan 1 12:00:00 host tinc.net[1234]: Read packet of length 46 from tap device
Jan 1 12:00:00 host tinc.net[1234]: Trying to look up 0.0.192.168 in connection list failed!
@end example
@itemize
@item Add the `ifconfig $NETNAME -arp' to tinc-up.
@end itemize

@item Network address and subnet mask do not match!

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

@item This is a bug: net.c:253: 24: Some error

@itemize
@item This is something that should not have happened.
Please report this, and tell us exactly what went wrong before you got
this message.  In normal operation, these errors should not occur.
@end itemize

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

@itemize
@item You must specify the complete pathname.
Specifying a relative path does not make sense here.  tinc changes its
directory to / when starting (to avoid keeping a mount point busy); and
even if we built in a default directory to look for these files, the key
files are bound to be in a different directory.
@end itemize

@end table

@c ==================================================================
@node    Technical information, About us, Running tinc, Top
@chapter Technical information


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


@c ==================================================================
@node    The connection, The meta-protocol, Technical information, Technical information
@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, The meta-connection, The connection, The connection
@subsection The UDP tunnel

@cindex ethertap
@cindex frame type
The data itself is read from a character device file, the so-called
@emph{ethertap} 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.  Data to
and from the device is formatted as if it were a normal Ethernet card,
so a frame is preceded by two MAC addresses and a @emph{frame type}
field.

So when tinc reads an Ethernet frame from the device, it determines its
type.  Right now, tinc can only handle Internet Protocol version 4 (IPv4)
frames, because it needs IP headers for routing.
Plans to support other protocols and switching instead of routing are being made.
(Some code for IPv6 routing and switching is already present but nonfunctional.)
When tinc knows
which type of frame it has read, it can also read the source and
destination address from it.

Now it is time that the frame gets encrypted.  Currently the only
encryption algorithm available is blowfish.

@cindex encapsulating
@cindex UDP
When the encryption is ready, 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 does a decrypt on the contents of the UDP datagram,
and it writes the decrypted information to its own ethertap device.

To let the kernel on the receiving end accept the packet, the destination MAC
address must match that of the tap interface. Because of the routing nature
of tinc, ARP is not possible. tinc solves this by always overwriting the
destination MAC address with fe:fd:0:0:0:0. That is also the reason why you must
set the MAC address of your tap interface to that address.


@c ==================================================================
@node    The meta-connection,  , The UDP tunnel, The connection
@subsection The meta-connection

Having only an 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, Security, The connection, Technical information
@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 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
succesful 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_HOST
@cindex ADD_SUBNET
@example
daemon  message
--------------------------------------------------------------------------
origin  ADD_HOST daemon a329e18c:655 0
                    |         |      +--> options
                    |         +---------> real address:port
                    +-------------------> name of new tinc daemon
origin  ADD_SUBNET daemon 1,0a010100/ffffff00
                      |   |     |       +--> netmask
                      |   |     +----------> vpn IPv4 network address
                      |   +----------------> subnet type (1=IPv4)
                      +--------------------> owner of this subnet
--------------------------------------------------------------------------
@end example

@cindex DEL_HOST
@cindex DEL_SUBNET
In case daemons leave the VPN, DEL_HOST and DEL_SUBNET messages with exactly
the same syntax are sent to inform the other daemons of the departure.

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. If any hop on the way has already learned the key, it will
act as a proxy and forward it's copy back to the requestor.

@cindex REQ_KEY
@cindex ANS_KEY
@cindex KEY_CHANGED
@example
daemon  message
--------------------------------------------------------------------------
daemon  REQ_KEY origin destination
                   |       +--> name of the tinc daemon it wants the key from
                   +----------> name of the daemon that wants the key      
daemon  ANS_KEY origin destination e4ae0b0a82d6e0078179b5290c62c7d0
                   |       |       \______________________________/
                   |       |                      +--> 128 bits key
                   |       +--> name of the daemon that wants the key
                   +----------> name of the daemon that uses this key
daemon  KEY_CHANGED origin
                      +--> daemon that has changed it's packet key
--------------------------------------------------------------------------
@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.

@cindex PING
@cindex PONG
@example
daemon  message
--------------------------------------------------------------------------
origin  PING 9e76
             \__/
               +--> 2 bytes of salt (random data)
dest.   PONG 3b8d
             \__/
               +--> 2 bytes of salt (random data)
--------------------------------------------------------------------------
@end example

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


@c ==================================================================
@node    Security,  , The meta-protocol, Technical information
@section About tinc's encryption and other security-related issues.

@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 uses blowfish encryption in CBC mode and a small amount of salt
at the beginning of each packet to make sure eavesdroppers cannot get
any information at all from the packets they can intercept.

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


@c ==================================================================
@node    Authentication protocol, Encryption of network packets, Security, Security
@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.

@example
daemon  message
--------------------------------------------------------------------------
client  <attempts connection>

server  <accepts connection>

client  ID client 10 0
              |    | +-> options
              |    +---> version
              +--------> name of tinc daemon

server  ID server 10 0
              |    | +-> options
              |    +---> 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 encrypt outgoing traffic using S1
 - the server will 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
--------------------------------------------------------------------------
@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 send 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,  , Authentication protocol, Security
@subsection Encryption of network packet
@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 retreive 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 | salt | VPN packet | UDP trailer
                             \___________________/
                                       |
                                       V
                         Encrypted with symmetric cipher
@end example

So, the entire UDP payload is encrypted using a symmetric cipher (blowfish in CBC mode).
2 bytes of salt (random data) are added in front of the actual VPN packet,
so that two VPN packets with (almost) the same content do not seem to be
the same for eavesdroppers.
2 bytes of salt may not seem much, but you can encrypt 65536 identical packets
now without an attacker being able to see that they were identical.
Given a MTU of 1500 this means 96 Megabyte of data.

There is no @emph{extra} provision against replay attacks or alteration of packets.
However, the VPN packets, normally UDP or TCP packets themselves, contain
checksums and sequence numbers.
Since those checksums and sequence numbers are encrypted,
they automatically become @emph{cryptographically secure}.
The kernel will handle any checksum errors and duplicate packets.


@c ==================================================================
@node    About us, Concept Index, Technical information, Top
@chapter About us


@menu
* Contact Information::
* Authors::
@end menu


@c ==================================================================
@node    Contact Information, Authors, About us, About us
@section Contact information

@cindex website
tinc's website is at @url{http://tinc.nl.linux.org/},
this server is located in the Netherlands.

@cindex IRC
We have an IRC channel on the Open Projects IRC network.  Connect to
@uref{http://openprojects.nu/services/irc.html, irc.openprojects.net},
and join channel #tinc.


@c ==================================================================
@node    Authors,  , Contact Information, About us
@section Authors

@table @asis
@item Ivo Timmermans (zarq) (@email{itimmermans@@bigfoot.com})
Main coder/hacker and maintainer of the package.

@item Guus Sliepen (guus) (@email{guus@@sliepen.warande.net})
Originator of it all, co-author.

@item Wessel Dankers (Ubiq) (@email{wsl@@nl.linux.org})
For the name `tinc' and various suggestions.

@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,  , About us, Top
@c        node-name,    next, previous,        up
@unnumbered Concept Index

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


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