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

Copyright © 1998-2002 Ivo Timmermans <itimmermans@bigfoot.com>, Guus Sliepen <guus@sliepen.warande.net> and Wessel Dankers <wsl@nl.linux.org>.

$Id: tinc.texi,v 1.8.4.22 2002/03/01 13:38:02 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.

Introduction
************

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.

Virtual Private Networks
========================

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.

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 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.

This problem can be solved by using 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.

tinc
====

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.

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.

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.

Supported platforms
===================

tinc has been verified to work under Linux, FreeBSD, OpenBSD and Solaris, 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.

For an up to date list of supported platforms, please check the list on our website: http://tinc.nl.linux.org/platforms.html.

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.

FreeBSD
-------

tinc on FreeBSD relies on the universal 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.

OpenBSD
-------

tinc on OpenBSD relies on the tun driver for its data acquisition from the kernel. It has been verified to work under at least OpenBSD 2.9.

Solaris
-------

tinc on Solaris relies on the universal 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.

Preparations
************

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

Configuring the kernel
======================

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'.

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 Kernel HOWTO (http://howto.linuxberg.com/LDP/HOWTO/Kernel-HOWTO.html) first.

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:

     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

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 /etc/modules.conf:

     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 tapN ethertap
     options tapN -o tapN unit=N

Add as much alias/options lines as necessary.

Configuration of Linux kernels 2.4.0 and higher
-----------------------------------------------

Here are the options you have to turn on when configuring a new kernel:

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

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 /etc/modules.conf:

     alias char-major-10-200 tun

Configuration of FreeBSD kernels
--------------------------------

This section will contain information on how to configure your FreeBSD kernel to support the universal tun/tap device.  For 4.1 and higher versions, this is included in the default kernel configuration, for earlier systems (4.0 and earlier), you need to install the universal tun/tap driver yourself.

Unfortunately somebody still has to write the text.

Configuration of OpenBSD kernels
--------------------------------

This section will contain information on how to configure your OpenBSD kernel to support the tun device.  For 2.9 and 3.0 systems, this is included in the default kernel configuration.

Unfortunately somebody still has to write the text.

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.

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.

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 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 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.

     --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)

License
.......

Since the license under which OpenSSL is distributed is not directly compatible with the terms of the GNU GPL http://www.openssl.org/support/faq.html#LEGAL2, therefore we include an addition to the GPL (see also the file COPYING.README):

     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.

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 download page (http://tinc.nl.linux.org/download.html), 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 INSTALL, which is included in the source distribution.

Building and installing tinc
============================

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

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.

System files
============

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

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:

     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/tapN c 36 N+16
     chown 0.0 /dev/tapN

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):

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

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 /dev/misc/net/tun.

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

Other files
-----------

/etc/networks
.............

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

     myvpn 10.0.0.0

/etc/services
.............

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

     tinc            655/tcp    TINC
     tinc            655/udp    TINC
     #                          Ivo Timmermans <itimmermans@bigfoot.com>

Configuration
*************

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? 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 Linux Network Administrators Guide (http://www.linuxdoc.org/LDP/nag2/).

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.

Multiple networks
=================

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.

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.

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.

Configuration files
===================

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

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

     Variable = Value.

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 bold.

Main configuration variables
----------------------------

AddressFamily = <ipv4|ipv6|any> (ipv4) [experimental]
     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.

     Mixing IPv4 and IPv6 may not work as desired. It's best to choose one address family and use that for all tinc daemons on the VPN.

BindToInterface = <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.

BindToIP = <address> [experimental]
     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.

     This option may not work on all platforms.

ConnectTo = <name>
     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.

Device = <device> (/dev/tap0 or /dev/misc/net/tun)
     The virtual network device to use.  Note that you can only use one device per daemon.  See also Device files.

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.

Interface = <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. Currently this option only affects the Linux tun/tap device.

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

     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.

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

     hub
          In this mode every packet will be broadcast to the other daemons.

KeyExpire = <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.

Name = <name>
     This is a symbolic name for this connection.  It can be anything

PingTimeout = <seconds> (60)
     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.

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.

PrivateKey = <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.

PrivateKeyFile = <path> [recommended]
     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.

     Note that there must be exactly one of PrivateKey or PrivateKeyFile specified in the configuration file.

Host configuration variables
----------------------------

Address = <IP address|hostname> [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.

Cipher = <cipher> (blowfish)
     The symmetric cipher algorithm used to encrypt UDP packets. Any cipher supported by OpenSSL is recognized.

Compression = <level> (0)
     This option sets the level of compression used for UDP packets. Possible values are 0 (off), 1 (fast) and any integer up to 9 (best).

Digest = <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.

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

MACLength = <length> (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.

Port = <port> (655)
     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.

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

PublicKeyFile = <path> [obsolete]
     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.

     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 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.

Subnet = <address[/masklength]>
     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 masklength. 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!

     masklength 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 RFC1519 (ftp://ftp.isi.edu/in-notes/rfc1519.txt)

TCPonly = <yes|no> (no) [experimental]
     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.

How to configure
----------------

Step 1. Creating the main configuration file
............................................

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

     Name = yourname
     Device = /dev/tap0
     PrivateKeyFile = /etc/tinc/netname/rsa_key.priv

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

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 /etc/tinc/netname/hosts/yourname. Adapt the following example to create a host configuration file:

     Address = your.real.hostname.org
     Subnet = 192.168.1.0/24

You can also use an IP address instead of a hostname. The `Subnet' specifies the address range that is local for 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).

Generating keypairs
===================

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:

     tincd -n netname -K

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

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 (/dev/tun, /dev/tap0 or similar), which will also create a network interface called something like `tun0', `tap0', or, if you are using the Linux tun/tap driver, the network interface will by default have the same name as the netname.

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

An example tinc-up script:

     #!/bin/sh
     ifconfig $INTERFACE hw ether fe:fd:0:0:0:0
     ifconfig $INTERFACE 192.168.1.1 netmask 255.255.0.0
     ifconfig $INTERFACE -arp

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:0:0:0:0 for tinc to work in it's normal mode. If you configured tinc to work in `switch' or `hub' mode, the hardware address should instead be set to a unique address instead of fe:fd:0:0:0:0.

You can use the environment variable $INTERFACE to get the name of the interface. If you are using the ethertap driver however, you need to replace it with tapN, corresponding to the device file name.

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 tinc-up script. The kernel will also bring the interface up after this command. The netmask is the mask of the entire VPN network, not just your own subnet.

The last line tells the kernel not to use ARP on that interface. Again this has to do with how Ethernet and tinc work. Use this option only if you are running tinc under Linux and are using tinc's normal routing mode.

Example configuration
=====================

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.

     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

``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.

For Branch A
............

BranchA would be configured like this:

In /etc/tinc/company/tinc-up:

     # 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:0:0:0:0
     ifconfig tap0 10.1.54.1 netmask 255.0.0.0
     ifconfig tap0 -arp

and in /etc/tinc/company/tinc.conf:

     Name = BranchA
     PrivateKey = /etc/tinc/company/rsa_key.priv
     Device = /dev/tap0

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

     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-----

For Branch B
............

In /etc/tinc/company/tinc-up:

     # 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:0:0:0:0
     ifconfig tap0 10.2.1.12 netmask 255.0.0.0
     ifconfig tap0 -arp

and in /etc/tinc/company/tinc.conf:

     Name = BranchB
     ConnectTo = BranchA
     PrivateKey = /etc/tinc/company/rsa_key.priv

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 /etc/tinc/company/hosts/BranchB:

     Subnet = 10.2.0.0/16
     Address = 2.3.4.5

     -----BEGIN RSA PUBLIC KEY-----
     ...
     -----END RSA PUBLIC KEY-----

For Branch C
............

In /etc/tinc/company/tinc-up:

     # 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:0:0:0:0
     ifconfig tap1 10.3.69.254 netmask 255.0.0.0
     ifconfig tap1 -arp

and in /etc/tinc/company/tinc.conf:

     Name = BranchC
     ConnectTo = BranchA
     Device = /dev/tap1

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 /etc/tinc/company/hosts/BranchC:

     Address = 3.4.5.6
     Subnet = 10.3.0.0/16
     Port = 2000

     -----BEGIN RSA PUBLIC KEY-----
     ...
     -----END RSA PUBLIC KEY-----

For Branch D
............

In /etc/tinc/company/tinc-up:

     # 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

and in /etc/tinc/company/tinc.conf:

     Name = BranchD
     ConnectTo = BranchC
     Device = /dev/misc/net/tun
     PrivateKeyFile = /etc/tinc/company/rsa_key.priv

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 /etc/tinc/company/hosts/BranchD:

     Subnet = 10.4.0.0/16
     Address = 4.5.6.7

     -----BEGIN RSA PUBLIC KEY-----
     ...
     -----END RSA PUBLIC KEY-----

Key files
.........

A, B, C and D all have generated a public/private keypair with the following command:

     tincd -n company -K

The private key is stored in /etc/tinc/company/rsa_key.priv, the public key is put into the host configuration file in the /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 tinc.conf file (if it is available).

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.

Running tinc
************

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

     tincd -n netname

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.

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.

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

-c, --config=PATH
     Read configuration options from the directory PATH.  The default is /etc/tinc/netname/.

-d, --debug=LEVEL
     Set debug level to LEVEL.  The higher the debug level, the more gets logged.  Everything goes via syslog.

-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.

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

-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.NETNAME.pid. Use it in conjunction with the -n option to make sure you kill the right tinc daemon.

-n, --net=NETNAME
     Connect to net NETNAME.  See Multiple networks.

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

--version
     Output version information and exit.

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!

Could not open /dev/tap0: No such device

       * You forgot to `modprobe netlink_dev' or `modprobe ethertap'.

       * You forgot to compile `Netlink device emulation' in the kernel.

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

       * You forgot to `modprobe tun'.

       * You forgot to compile `Universal TUN/TAP driver' in the kernel.

Packet with destination 1.2.3.4 is looping back to us!

       * 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 netmask which is just as large as the netmask 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!

       * 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.

Network doesn't work, syslog shows only packets of length 46

          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!

       * Add the `ifconfig $INTERFACE -arp' to tinc-up.

Network address and subnet mask do not match!

       * The Subnet field must contain a network address.

       * If you only want to use one IP address, set the netmask to /32.

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

       * 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.

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

       * 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.

Technical information
*********************

The connection
==============

tinc is a daemon that takes VPN data and transmit that to another host computer over the existing Internet infrastructure.

The UDP tunnel
--------------

The data itself is read from a character device file, the so-called 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.  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 frame type field.

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. 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).

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

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 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.

To let the kernel on the receiving end accept the packet, 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 cannot be set by the sending daemons. 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.

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.

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.

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.

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 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.

     daemon	message
     --------------------------------------------------------------------------
     origin	ADD_EDGE node1 12.23.34.45 655 node2 21.32.43.54 655 222 0
                         |       |       |  \___________________/  |  +-> options
                         |       |       |             |           +----> weight
     		    |       |       |             +----------------> see below
     		    |       |       +--> UDP port
     		    |       +----------> real address
                         +------------------> name of node on one side of the edge

     origin	ADD_SUBNET node 192.168.1.0/24
                          |         |     +--> masklength
                          |         +--------> IPv4 network address
                          +------------------> owner of this subnet
     --------------------------------------------------------------------------

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.

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 its copy back to the requester.

     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 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

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

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.

     daemon	message
     --------------------------------------------------------------------------
     origin	PING
     dest.	PONG
     --------------------------------------------------------------------------

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

About tinc's encryption and other security-related issues.
==========================================================

tinc got its name from ``TINC,'' short for 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 don't want, we named the tinc project after TINC.

But in order to be ``immune'' to eavesdropping, you'll have to encrypt your data.  Because tinc is a Secure VPN (SVPN) daemon, it does exactly that: encrypt. tinc uses blowfish encryption in CBC mode, sequence numbers and message authentication codes to make sure eavesdroppers cannot get and cannot change any information at all from the packets they can intercept.

Authentication protocol
-----------------------

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.

     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 12.23.34.45 123 0
                  |       |       |  +-> options
     	     |       |       +----> estimated weight
     	     |       +------------> IP address of server as seen by client
     	     +--------------------> UDP port of client

     server  ACK 655 21.32.43.54 321 0
                  |       |       |  +-> options
     	     |       |       +----> estimated weight
     	     |       +------------> IP address of client as seen by server
     	     +--------------------> UDP port of server
     --------------------------------------------------------------------------

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.

Encryption of network packet
----------------------------

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.

The UDP packet containing the network packet from the VPN has the following layout:

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

So, the entire VPN packet is encrypted using a symmetric cipher. A 32 bits sequence number 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.

About us
********

Contact information
===================

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

We have an IRC channel on the Open Projects IRC network.  Connect to irc.openprojects.net (http://openprojects.nu/services/irc.html), and join channel #tinc.

Authors
=======

Ivo Timmermans (zarq) (itimmermans@bigfoot.com)
     Main coder/hacker and maintainer of the package.

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

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

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 THANKS in the source distribution.