                                ==============
                                The TINC HOWTO
                                ==============

                                Wessel Dankers
                               wsl@nl.linux.org

Introduction
------------
Tinc is a system to create a virtual ethernet network on top of an existing
infrastructure. This infrastructure can be anything from modem lines to
gigabit ethernet networks, as long as they talk IP. Once you install and
configure tinc, your host will get an extra IP address, just like it would
when you stick an extra ethernet card into it. Using this IP address, it can
communicate with all hosts in its virtual network using strong encryption.

If you install Tinc on a router (and pick your numbers correctly) you can
have the router forward all packets. This way you can---instead of
connecting hosts---connect entire sites together! Now you need only one
outgoing network connection for both internet and intranet.

Architecture
------------
When a few Tinc daemons are running they will try to seek contact with
eachother. A daemon is all the time connected to a few other daemons,
but if traffic is required with a daemon it doesn't know yet, it will
instantly contact it and exchange keys. These so-called meta-connections
are made over TCP, using encryption of course.

When actual traffic has to be sent, a daemon checks his connection list to
see if the addressee is known (and makes contact with it if neccessary).
All packets are then sent using UDP to the other host, just like in a real
network. If a packet gets lost, the connection layer of Linux will resend
the packet, just like it would over a normal network.

Once in a while the daemons will renegotiate keys so that even if a cracker
breaks one, it'll be of limited use.

Getting Tinc
------------
Before you fetch the latest tarball, you might want to check if there's a
package for your Linux distribution. One of the main authors is a Debian
Developer, so you can expect the Debian packages to be very up to date.

The official website for Tinc can be found at http://tinc.nl.linux.org/.
There you can find Debian packages, RPM's and of course... the tarball!
Since we run Doohickey Linux Pro 1.0, for which no package exists (or
indeed the distribution itself) we shall compile the package ourselves.

Building
--------
The Tinc source adheres to so many standards it makes you head spin.
Even the debug messages have been localized! Amazing. Tinc also comes
with a configuration script. If you like to see what is there to
configure run ./configure --help | more. If you don't have time for such
nonsense:

	./configure --sysconfdir=/etc

This will see if your system is nice enough to run tinc on, and will
create some Makefiles and other stuff which will together build tinc.

	make
	make install

The first will do the actual build, the second copies all files into place.

The kernel
----------
Next you will have to configure the kernel to support the tap device.
It is important that you run a recent kernel, but anything after 2.2.16
will do. You have to enable both the netlink device AND the ethertap
device (in that order). Enable them as modules!
Compile, install =) You don't even have to reboot.

Picking your numbers
--------------------
The first thing we should do is pick network numbers. Tinc has a very
peculiar taste for network numbers, which is caused by the way it routes
traffic. However, it turns out to be really handy if you want to use
your tinc host as a router for a site.

The numbers have to be in a range that is not yet in use in your existing,
real network! In this example we will use numbers from the 192.168.0/16
range. This is standard CIDR notation for all IP addresses from 192.168.0.0
to 192.168.255.255. The /16 means that the first 16 bits form the network
part.

It is common practice for Tinc networks to use private (RFC 1918) addresses.
This is not necessary, but it would be a waste to use official addresses
for a private network!

In the example we will connect three machines: f00f, fdiv and hlt. We will
give each an address, but not just that, also a slice of our address space
to play with.

      Host          Real address           Tinc network
      ---------------------------------------------------
      f00f          126.202.37.20          192.168.1.1/24
      fdiv          126.202.37.81          192.168.2.1/24
      hlt           103.22.1.218           192.168.3.1/24

It is very important that none of the Tinc netmasks overlap! Note how the
192.168.0/16 network covers the entire address space of the three hosts.
We will refer to the 192.168.0/16 network as the `umbrella' from now on.
As you can see we can fit 256 hosts into this umbrella this way, which is
also the practical maximum for tinc. Let's name our VPN 'fubar'.

The configuration file
----------------------
Let's create a configuration file for f00f. We have to put it in
/etc/tinc/fubar because that's how we named our VPN.

	MyOwnVPNIP = 192.168.1.1/24
	VpnMask    = 255.255.0.0
	ConnectTo  = 126.202.37.81
	ConnectTo  = 103.22.1.218
	TapDevice  = /dev/tap0

The first two lines tell Tinc about the numbers we have chosen above.
Using the ConnectTo lines, the daemon will seek contact with the rest of
the umbrella. It's possible to configure any number of ConnectTo lines,
you can even omit them so that it just sits and waits until someone else
contacts it. Until someone does, the poor daemon won't be able to send
any data because it doesn't know where everybody is.
The TapDevice is where the tinc daemon will interface with the kernel.

The passphrases
---------------
We will have to generate keys for ourselves, and get a key from everybody
we want to ConnectTo. All of these go into a directory named
/etc/tinc/fubar/passphrases. PROTECT THIS DIRECTORY!

	mkdir -m 700 /etc/tinc/fubar/passphrases

To generate our own key:

	genauth 1024 >/etc/tinc/fubar/passphrases/local

You should then proceed to give this key to anyone who wants to ConnectTo
you. DO THIS IN A SECURE MANNER! Anyone who has this number can do icky
things to the umbrella network! Encrypt it using PGP, GPG or another
program using asymmetric keys. Read it over the phone (without anyone
listening of course). Send it by snailmail. Write the key down and bring
it to your partners personally!

If you get any keys from your partners, store them under their network
number. For example, the key we get from fdiv's network administrator
will be stored in /etc/tinc/fubar/passphrases/192.168.2.0 (note the 0).

Running the daemon
------------------
If you use a package manager to install Tinc, the startup scripts use a file
called /etc/tinc/nets.boot to see which umbrella's exist. It has a line
per VPN, and lines starting with a # are ignored. Ours will contain:

	# Example VPN from the HOWTO
	fubar

In Debian, /etc/init.d/tinc start will start the daemons.

If you use Doohickey Linux just like we do, you'll have to edit the systems
startup scripts by hand. It should contain something along the lines of:

	insmod ethertap -s --name=tap0 unit=0
	ifconfig tap0 hw ether fe:fd:c0:a8:01:01
	ifconfig tap0 192.168.1.1 netmask 255.255.0.0 broadcast 192.168.255.255 -arp

There are two things to note here! First, the MAC address of the ethertap
device is very important. It must start with fe:fd, and end in the
hexadecimal representation of the VPN IP number.
Second, the netmask of the tap device is set to that of the umbrella!

--
$Id: HOWTO,v 1.2.2.3 2000/07/01 07:29:32 wsl Exp $
