175 lines
7.4 KiB
Text
175 lines
7.4 KiB
Text
==============
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The TINC HOWTO
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==============
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Wessel Dankers
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wsl@nl.linux.org
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Introduction
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------------
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Tinc is a system to create a virtual ethernet network on top of an existing
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infrastructure. This infrastructure can be anything from modem lines to
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gigabit ethernet networks, as long as they talk IP. Once you install and
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configure tinc, your host will get an extra IP address, just like it would
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when you stick an extra ethernet card into it. Using this IP address, it can
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communicate with all hosts in its virtual network using strong encryption.
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If you install Tinc on a router (and pick your numbers correctly) you can
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have the router forward all packets. This way you can---instead of
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connecting hosts---connect entire sites together! Now you need only one
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outgoing network connection for both internet and intranet.
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Architecture
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------------
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When a few Tinc daemons are running they will try to seek contact with
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eachother. A daemon is all the time connected to a few other daemons,
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but if traffic is required with a daemon it doesn't know yet, it will
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instantly contact it and exchange keys. These so-called meta-connections
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are made over TCP, using encryption of course.
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When actual traffic has to be sent, a daemon checks his connection list to
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see if the addressee is known (and makes contact with it if neccessary).
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All packets are then sent using UDP to the other host, just like in a real
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network. If a packet gets lost, the connection layer of Linux will resend
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the packet, just like it would over a normal network.
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Once in a while the daemons will renegotiate keys so that even if a cracker
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breaks one, it'll be of limited use.
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Getting Tinc
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------------
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Before you fetch the latest tarball, you might want to check if there's a
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package for your Linux distribution. One of the main authors is a Debian
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Developer, so you can expect the Debian packages to be very up to date.
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The official website for Tinc can be found at http://tinc.nl.linux.org/.
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There you can find Debian packages, RPM's and of course... the tarball!
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Since we run Doohickey Linux Pro 1.0, for which no package exists (or
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indeed the distribution itself) we shall compile the package ourselves.
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Building
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--------
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The Tinc source adheres to so many standards it makes you head spin.
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Even the debug messages have been localized! Amazing. Tinc also comes
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with a configuration script. If you like to see what is there to
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configure run ./configure --help | more. If you don't have time for such
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nonsense:
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./configure --sysconfdir=/etc
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This will see if your system is nice enough to run tinc on, and will
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create some Makefiles and other stuff which will together build tinc.
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make
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make install
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The first will do the actual build, the second copies all files into place.
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The kernel
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----------
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Next you will have to configure the kernel to support the tap device.
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It is important that you run a recent kernel, but anything after 2.2.16
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will do. You have to enable both the netlink device AND the ethertap
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device (in that order). Enable them as modules!
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Compile, install =) You don't even have to reboot.
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Picking your numbers
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--------------------
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The first thing we should do is pick network numbers. Tinc has a very
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peculiar taste for network numbers, which is caused by the way it routes
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traffic. However, it turns out to be really handy if you want to use
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your tinc host as a router for a site.
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The numbers have to be in a range that is not yet in use in your existing,
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real network! In this example we will use numbers from the 192.168.0/16
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range. This is standard CIDR notation for all IP addresses from 192.168.0.0
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to 192.168.255.255. The /16 means that the first 16 bits form the network
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part.
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It is common practice for Tinc networks to use private (RFC 1918) addresses.
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This is not necessary, but it would be a waste to use official addresses
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for a private network!
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In the example we will connect three machines: f00f, fdiv and hlt. We will
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give each an address, but not just that, also a slice of our address space
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to play with.
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Host Real address Tinc network
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---------------------------------------------------
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f00f 126.202.37.20 192.168.1.1/24
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fdiv 126.202.37.81 192.168.2.1/24
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hlt 103.22.1.218 192.168.3.1/24
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It is very important that none of the Tinc netmasks overlap! Note how the
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192.168.0/16 network covers the entire address space of the three hosts.
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We will refer to the 192.168.0/16 network as the `umbrella' from now on.
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As you can see we can fit 256 hosts into this umbrella this way, which is
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also the practical maximum for tinc. Let's name our VPN 'fubar'.
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The configuration file
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----------------------
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Let's create a configuration file for f00f. We have to put it in
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/etc/tinc/fubar because that's how we named our VPN.
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MyOwnVPNIP = 192.168.1.1/24
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VpnMask = 255.255.0.0
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ConnectTo = 126.202.37.81
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ConnectTo = 103.22.1.218
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TapDevice = /dev/tap0
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The first two lines tell Tinc about the numbers we have chosen above.
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Using the ConnectTo lines, the daemon will seek contact with the rest of
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the umbrella. It's possible to configure any number of ConnectTo lines,
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you can even omit them so that it just sits and waits until someone else
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contacts it. Until someone does, the poor daemon won't be able to send
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any data because it doesn't know where everybody is.
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The TapDevice is where the tinc daemon will interface with the kernel.
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The passphrases
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---------------
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We will have to generate keys for ourselves, and get a key from everybody
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we want to ConnectTo. All of these go into a directory named
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/etc/tinc/fubar/passphrases. PROTECT THIS DIRECTORY!
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mkdir -m 700 /etc/tinc/fubar/passphrases
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To generate our own key:
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genauth 1024 >/etc/tinc/fubar/passphrases/local
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You should then proceed to give this key to anyone who wants to ConnectTo
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you. DO THIS IN A SECURE MANNER! Anyone who has this number can do icky
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things to the umbrella network! Encrypt it using PGP, GPG or another
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program using asymmetric keys. Read it over the phone (without anyone
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listening of course). Send it by snailmail. Write the key down and bring
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it to your partners personally!
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If you get any keys from your partners, store them under their network
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number. For example, the key we get from fdiv's network administrator
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will be stored in /etc/tinc/fubar/passphrases/192.168.2.0 (note the 0).
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Running the daemon
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------------------
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If you use a package manager to install Tinc, the startup scripts use a file
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called /etc/tinc/nets.boot to see which umbrella's exist. It has a line
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per VPN, and lines starting with a # are ignored. Ours will contain:
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# Example VPN from the HOWTO
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fubar
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In Debian, /etc/init.d/tinc start will start the daemons.
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If you use Doohickey Linux just like we do, you'll have to edit the systems
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startup scripts by hand. It should contain something along the lines of:
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insmod ethertap -s --name=tap0 unit=0
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ifconfig tap0 hw ether fe:fd:c0:a8:01:01
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ifconfig tap0 192.168.1.1 netmask 255.255.0.0 broadcast 192.168.255.255 -arp
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There are two things to note here! First, the MAC address of the ethertap
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device is very important. It must start with fe:fd, and end in the
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hexadecimal representation of the VPN IP number.
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Second, the netmask of the tap device is set to that of the umbrella!
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--
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$Id: HOWTO,v 1.6 2002/04/12 08:25:01 guus Exp $
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