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.IX Title "GVPE 5"
.TH GVPE 5 "2005-03-26" "1.9" "GNU Virtual Private Ethernet"
.SH "NAME"
GNU\-VPE \- Overview of the GNU Virtual Private Ethernet suite.
.SH "DESCRIPTION"
.IX Header "DESCRIPTION"
\&\s-1GVPE\s0 is a suite designed to provide a virtual private network for multiple
nodes over an untrusted network. This document first gives an introduction
to VPNs in general and then describes the specific implementation of \s-1GVPE\s0.
.Sh "\s-1WHAT\s0 \s-1IS\s0 A \s-1VPN\s0?"
.IX Subsection "WHAT IS A VPN?"
\&\s-1VPN\s0 is an acronym, it stands for:
.IP "\(bu" 4
.IX Xref "Virtual"
Virtual means that no physical network is created (of course), but a
network is \fIemulated\fR by creating multiple tunnels between the member
nodes by encapsulating and sending data over another transport network.
.Sp
Usually the emulated network is a normal \s-1IP\s0 or Ethernet, and the transport
network is the Internet. However, using a \s-1VPN\s0 system like \s-1GVPE\s0 to connect
nodes over other untrusted networks such as Wireless \s-1LAN\s0 is not uncommon.
.IP "\(bu" 4
.IX Xref "Private"
Private means that non-participating nodes cannot decode (\*(L"sniff)\*(R" nor
inject (\*(L"spoof\*(R") packets. This means that nodes can be connected over
untrusted networks such as the public Internet without fear of being
eavesdropped while at the same time being able to trust data sent by other
nodes.
.Sp
In the case of \s-1GVPE\s0, even participating nodes cannot sniff packets
send to other nodes or spoof packets as if sent from other nodes, so
communications between any two nodes is private to those two nodes.
.IP "\(bu" 4
.IX Xref "Network"
Network means that more than two parties can participate in the network,
so for instance it's possible to connect multiple branches of a company
into a single network. Many so-called \*(L"vpn\*(R" solutions only create
point-to-point tunnels, which in turn can be used to build larger
networks.
.Sp
\&\s-1GVPE\s0 provides a true multi-point network in wich any number of nodes (at
least a few dozen in practise, the theoretical limit is 4095 nodes) can
participate.
.Sh "\s-1GVPE\s0 \s-1DESIGN\s0 \s-1GOALS\s0"
.IX Subsection "GVPE DESIGN GOALS"
.IP "\s-1SIMPLE\s0 \s-1DESIGN\s0" 4
.IX Item "SIMPLE DESIGN"
Cipher, \s-1HMAC\s0 algorithms and other key parameters must be selected
at compile time \- this makes it possible to only link in algorithms
you actually need. It also makes the crypto part of the source very
transparent and easy to inspect, and last not least this makes it possible
to hardcode the layout of all packets into the binary. \s-1GVPE\s0 goes a step
further and internally reserves blocks of the same length for all packets,
which virtually removes all possibilities of buffer overflows, as there is
only a single type of buffer and it's always of fixed length.
.IP "\s-1EASY\s0 \s-1TO\s0 \s-1SETUP\s0" 4
.IX Item "EASY TO SETUP"
A few lines of config (the config file is shared unmodified between all
hosts) and a single run of \f(CW\*(C`gvpectrl\*(C'\fR to generate the keys suffices to
make it work.
.IP "MAC-BASED \s-1SECURITY\s0" 4
.IX Item "MAC-BASED SECURITY"
Since every host has it's own private key, other hosts cannot spoof
traffic from this host. That makes it possible to filter packet by \s-1MAC\s0
address, e.g. to ensure that packets from a specific \s-1IP\s0 address come, in
fact, from a specific host that is associated with that \s-1IP\s0 and not from
another host.
.SH "PROGRAMS"
.IX Header "PROGRAMS"
Vpe comes with two programs: one daemon (\f(CW\*(C`gvpe\*(C'\fR) and one control program
(\f(CW\*(C`gvpectrl\*(C'\fR).
.IP "gvpectrl" 4
.IX Item "gvpectrl"
Is used to generate the keys, check and give an overview of of the
configuration and contorl the daemon (restarting etc.).
.IP "gvpe" 4
.IX Item "gvpe"
Is the daemon used to establish and maintain connections to the other
network members. It should be run on the gateway machine.
.SH "COMPILETIME CONFIGURATION"
.IX Header "COMPILETIME CONFIGURATION"
Please have a look at the \f(CW\*(C`gvpe.osdep(5)\*(C'\fR manpage for platform-specific
information.
.PP
Here are a few recipes for compiling your gvpe, showing the extremes
(fast, small, insecure \s-1OR\s0 slow, large, more secure), between you should
choose:
.Sh "\s-1AS\s0 \s-1LOW\s0 \s-1PACKET\s0 \s-1OVERHEAD\s0 \s-1AS\s0 \s-1POSSIBLE\s0"
.IX Subsection "AS LOW PACKET OVERHEAD AS POSSIBLE"
.Vb 1
\&   ./configure --enable-hmac-length=4 --enable-rand-length=0
.Ve
.PP
Minimize the header overhead of \s-1VPN\s0 packets (the above will result in
only 4 bytes of overhead over the raw ethernet frame). This is a insecure
configuration because a \s-1HMAC\s0 length of 4 makes collision attacks based on
the birthday paradox easy, though.
.Sh "\s-1MINIMIZE\s0 \s-1CPU\s0 \s-1TIME\s0 \s-1REQUIRED\s0"
.IX Subsection "MINIMIZE CPU TIME REQUIRED"
.Vb 1
\&   ./configure --enable-cipher=bf --enable-digest=md4
.Ve
.PP
Use the fastest cipher and digest algorithms currently available in
gvpe. \s-1MD4\s0 has been broken and is quite insecure, though.
.Sh "\s-1MAXIMIZE\s0 \s-1SECURITY\s0"
.IX Subsection "MAXIMIZE SECURITY"
.Vb 1
\&   ./configure --enable-hmac-length=16 --enable-rand-length=8 --enable-digest=sha1
.Ve
.PP
This uses a 16 byte \s-1HMAC\s0 checksum to authenticate packets (I guess 8\-12
would also be pretty secure ;) and will additionally prefix each packet
with 8 bytes of random data. In the long run, people should move to
\&\s-1SHA\-224\s0 and beyond, but support in openssl is missing as of writing this
document.
.PP
In general, remember that \s-1AES\-128\s0 seems to be more secure and faster than
\&\s-1AES\-192\s0 or \s-1AES\-256\s0, more randomness helps against sniffing and a longer
\&\s-1HMAC\s0 helps against spoofing. \s-1MD4\s0 is a fast digest, \s-1SHA1\s0 or \s-1RIPEMD160\s0 are
better, and Blowfish is a fast cipher (and also quite secure).
.SH "HOW TO SET UP A SIMPLE VPN"
.IX Header "HOW TO SET UP A SIMPLE VPN"
In this section I will describe how to get a simple \s-1VPN\s0 consisting of
three hosts up and running.
.Sh "\s-1STEP\s0 1: configuration"
.IX Subsection "STEP 1: configuration"
First you have to create a daemon configuation file and put it into the
configuration directory. This is usually \f(CW\*(C`/etc/gvpe\*(C'\fR, depending on how you
configured gvpe, and can be overwritten using the \f(CW\*(C`\-c\*(C'\fR commandline switch.
.PP
Put the following lines into \f(CW\*(C`/etc/gvpe/gvpe.conf\*(C'\fR:
.PP
.Vb 3
\&   udp-port = 50000 # the external port to listen on (configure your firewall)
\&   mtu = 1400       # minimum MTU of all outgoing interfaces on all hosts
\&   ifname = vpn0    # the local network device name
.Ve
.PP
.Vb 2
\&   node = first     # just a nickname
\&   hostname = first.example.net # the DNS name or IP address of the host
.Ve
.PP
.Vb 2
\&   node = second
\&   hostname = 133.55.82.9
.Ve
.PP
.Vb 2
\&   node = third
\&   hostname = third.example.net
.Ve
.PP
The only other file neccessary if the \f(CW\*(C`if\-up\*(C'\fR script that initializes the
local ethernet interface. Put the following lines into \f(CW\*(C`/etc/gvpe/if\-up\*(C'\fR
and make it execute (\f(CW\*(C`chmod 755 /etc/gvpe/if\-up\*(C'\fR):
.PP
.Vb 6
\&   #!/bin/sh
\&   ip link set $IFNAME address $MAC mtu $MTU up
\&   [ $NODENAME = first  ] && ip addr add 10.0.1.1 dev $IFNAME
\&   [ $NODENAME = second ] && ip addr add 10.0.2.1 dev $IFNAME
\&   [ $NODENAME = third  ] && ip addr add 10.0.3.1 dev $IFNAME
\&   ip route add 10.0.0.0/16 dev $IFNAME
.Ve
.PP
This script will give each node a different \s-1IP\s0 address in the \f(CW\*(C`10.0/16\*(C'\fR
network.  The internal network (e.g. the \f(CW\*(C`eth0\*(C'\fR interface) should then be
set to a subset of that network, e.g.  \f(CW\*(C`10.0.1.0/24\*(C'\fR on node \f(CW\*(C`first\*(C'\fR,
\&\f(CW\*(C`10.0.2.0/24\*(C'\fR on node \f(CW\*(C`second\*(C'\fR, and so on.
.PP
By enabling routing on the gateway host that runs \f(CW\*(C`gvpe\*(C'\fR all nodes will
be able to reach the other nodes. You can, of course, also use proxy arp
or other means of pseudo-bridging (or even real briding), or (best) full
routing \- the choice is yours.
.Sh "\s-1STEP\s0 2: create the \s-1RSA\s0 key pairs for all hosts"
.IX Subsection "STEP 2: create the RSA key pairs for all hosts"
Run the following command to generate all key pairs (that might take a
while):
.PP
.Vb 1
\&   gvpectrl -c /etc/gvpe -g
.Ve
.PP
This command will put the public keys into \f(CW\*(C`/etc/gvpe/pubkeys/\f(CInodename\f(CW\*(C'\fR and the private keys into \f(CW\*(C`/etc/gvpe/hostkeys/\f(CInodename\f(CW\*(C'\fR.
.Sh "\s-1STEP\s0 3: distribute the config files to all nodes"
.IX Subsection "STEP 3: distribute the config files to all nodes"
Now distribute the config files to the other nodes. This should be done in two steps, since the
private keys should not be distributed. The example uses rsync-over-ssh
.PP
First all the config files without the hostkeys should be distributed:
.PP
.Vb 3
\&   rsync -avzessh /etc/gvpe first.example.net:/etc/. --exclude hostkeys
\&   rsync -avzessh /etc/gvpe 133.55.82.9:/etc/. --exclude hostkeys
\&   rsync -avzessh /etc/gvpe third.example.net:/etc/. --exclude hostkeys
.Ve
.PP
Then the hostkeys should be copied:
.PP
.Vb 3
\&   rsync -avzessh /etc/gvpe/hostkeys/first  first.example.net:/etc/hostkey
\&   rsync -avzessh /etc/gvpe/hostkeys/second 133.55.82.9:/etc/hostkey
\&   rsync -avzessh /etc/gvpe/hostkeys/third  third.example.net:/etc/hostkey
.Ve
.PP
You should now check the configration by issuing the command \f(CW\*(C`gvpectrl \-c
/etc/gvpe \-s\*(C'\fR on each node and verify it's output.
.Sh "\s-1STEP\s0 4: starting gvpe"
.IX Subsection "STEP 4: starting gvpe"
You should then start gvpe on each node by issuing a command like:
.PP
.Vb 1
\&   gvpe -D -linfo first # first is the nodename
.Ve
.PP
This will make the gvpe stay in foreground. You should then see
\&\*(L"connection established\*(R" messages. If you don't see them check your
firewall and routing (use tcpdump ;).
.PP
If this works you should check your networking setup by pinging various
endpoints.
.PP
To make gvpe run more permanently you can either run it as a daemon
(by starting it without the \f(CW\*(C`\-D\*(C'\fR switch), or, much better, from your
inittab. I use a line like this on my systems:
.PP
.Vb 1
\&   t1:2345:respawn:/opt/gvpe/sbin/gvpe -D -L first >/dev/null 2>&1
.Ve
.Sh "\s-1STEP\s0 5: enjoy"
.IX Subsection "STEP 5: enjoy"
\&... and play around. Sending a \-HUP (\f(CW\*(C`gvpectrl \-kHUP\*(C'\fR) to the daemon
will make it try to connect to all other nodes again. If you run it from
inittab, as is recommended, \f(CW\*(C`gvpectrl \-k\*(C'\fR (or simply \f(CW\*(C`killall gvpe\*(C'\fR) will
kill the daemon, start it again, making it read it's configuration files
again.
.SH "SEE ALSO"
.IX Header "SEE ALSO"
\&\fIgvpe.osdep\fR\|(5) for OS-depedendent information, \fIgvpe.conf\fR\|(5), \fIgvpectrl\fR\|(8),
and for a description of the transports, protocol, and routing algorithm,
\&\fIgvpe.protocol\fR\|(7).
.PP
The \s-1GVPE\s0 mailinglist, at <http://lists.schmorp.de/>, or
\&\f(CW\*(C`gvpe@lists.schmorp.de\*(C'\fR.
.SH "AUTHOR"
.IX Header "AUTHOR"
Marc Lehmann <gvpe@schmorp.de>
.SH "COPYRIGHTS AND LICENSES"
.IX Header "COPYRIGHTS AND LICENSES"
\&\s-1GVPE\s0 itself is distributed under the \s-1GENERAL\s0 \s-1PUBLIC\s0 \s-1LICENSE\s0 (see the file
\&\s-1COPYING\s0 that should be part of your distribution).
.PP
In some configurations it uses modified versions of the tinc vpn suite,
which is also available under the \s-1GENERAL\s0 \s-1PUBLIC\s0 \s-1LICENSE\s0.