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Revision: 1.10
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# User Rev Content
1 pcg 1.1 =head1 NAME
2    
3     GNU-VPE - Overview of the GNU Virtual Private Ethernet suite.
4    
5     =head1 DESCRIPTION
6    
7     GVPE is a suite designed to provide a virtual private network for multiple
8 pcg 1.5 nodes over an untrusted network. This document first gives an introduction
9     to VPNs in general and then describes the specific implementation of GVPE.
10    
11     =head2 WHAT IS A VPN?
12    
13     VPN is an acronym, it stands for:
14 pcg 1.1
15 pcg 1.3 =over 4
16    
17 pcg 1.9 =item Virtual
18 pcg 1.3
19 pcg 1.5 Virtual means that no physical network is created (of course), but a
20     network is I<emulated> by creating multiple tunnels between the member
21     nodes by encapsulating and sending data over another transport network.
22    
23     Usually the emulated network is a normal IP or Ethernet, and the transport
24     network is the Internet. However, using a VPN system like GVPE to connect
25     nodes over other untrusted networks such as Wireless LAN is not uncommon.
26 pcg 1.1
27 pcg 1.9 =item Private
28 pcg 1.3
29     Private means that non-participating nodes cannot decode ("sniff)" nor
30 pcg 1.5 inject ("spoof") packets. This means that nodes can be connected over
31     untrusted networks such as the public Internet without fear of being
32     eavesdropped while at the same time being able to trust data sent by other
33     nodes.
34 pcg 1.1
35 pcg 1.5 In the case of GVPE, even participating nodes cannot sniff packets
36     send to other nodes or spoof packets as if sent from other nodes, so
37     communications between any two nodes is private to those two nodes.
38 pcg 1.1
39 pcg 1.9 =item Network
40 pcg 1.3
41     Network means that more than two parties can participate in the network,
42     so for instance it's possible to connect multiple branches of a company
43 pcg 1.8 into a single network. Many so-called "VPN" solutions only create
44 pcg 1.5 point-to-point tunnels, which in turn can be used to build larger
45     networks.
46    
47 pcg 1.8 GVPE provides a true multi-point network in which any number of nodes (at
48 pcg 1.5 least a few dozen in practise, the theoretical limit is 4095 nodes) can
49     participate.
50 pcg 1.1
51 pcg 1.3 =back
52    
53 pcg 1.5 =head2 GVPE DESIGN GOALS
54 pcg 1.1
55 root 1.10 =over 4
56 pcg 1.1
57     =item SIMPLE DESIGN
58    
59     Cipher, HMAC algorithms and other key parameters must be selected
60     at compile time - this makes it possible to only link in algorithms
61     you actually need. It also makes the crypto part of the source very
62 pcg 1.5 transparent and easy to inspect, and last not least this makes it possible
63     to hardcode the layout of all packets into the binary. GVPE goes a step
64     further and internally reserves blocks of the same length for all packets,
65     which virtually removes all possibilities of buffer overflows, as there is
66     only a single type of buffer and it's always of fixed length.
67 pcg 1.1
68     =item EASY TO SETUP
69    
70     A few lines of config (the config file is shared unmodified between all
71     hosts) and a single run of C<gvpectrl> to generate the keys suffices to
72     make it work.
73    
74     =item MAC-BASED SECURITY
75    
76     Since every host has it's own private key, other hosts cannot spoof
77     traffic from this host. That makes it possible to filter packet by MAC
78     address, e.g. to ensure that packets from a specific IP address come, in
79     fact, from a specific host that is associated with that IP and not from
80     another host.
81    
82     =back
83    
84     =head1 PROGRAMS
85    
86 pcg 1.8 Gvpe comes with two programs: one daemon (C<gvpe>) and one control program
87 pcg 1.1 (C<gvpectrl>).
88    
89     =over 4
90    
91     =item gvpectrl
92    
93 pcg 1.8 This program is used to generate the keys, check and give an overview of of the
94     configuration and to control the daemon (restarting etc.).
95 pcg 1.1
96     =item gvpe
97    
98 pcg 1.8 This is the daemon used to establish and maintain connections to the other
99     network nodes. It should be run on the gateway of each VPN subnet.
100 pcg 1.1
101     =back
102    
103     =head1 COMPILETIME CONFIGURATION
104    
105     Please have a look at the C<gvpe.osdep(5)> manpage for platform-specific
106     information.
107    
108 pcg 1.8 Gvpe hardcodes most encryption parameters. While this reduces flexibility,
109     it makes the program much simpler and helps making buffer overflows
110     impossible under most circumstances.
111    
112 pcg 1.4 Here are a few recipes for compiling your gvpe, showing the extremes
113 pcg 1.8 (fast, small, insecure OR slow, large, more secure), between which you
114     should choose:
115 pcg 1.1
116     =head2 AS LOW PACKET OVERHEAD AS POSSIBLE
117    
118     ./configure --enable-hmac-length=4 --enable-rand-length=0
119    
120 pcg 1.4 Minimize the header overhead of VPN packets (the above will result in
121     only 4 bytes of overhead over the raw ethernet frame). This is a insecure
122     configuration because a HMAC length of 4 makes collision attacks based on
123 pcg 1.8 the birthday paradox pretty easy.
124 pcg 1.1
125     =head2 MINIMIZE CPU TIME REQUIRED
126    
127     ./configure --enable-cipher=bf --enable-digest=md4
128    
129 pcg 1.4 Use the fastest cipher and digest algorithms currently available in
130 pcg 1.8 gvpe. MD4 has been broken and is quite insecure, though, so using another
131     digest algorithm is recommended.
132 pcg 1.1
133     =head2 MAXIMIZE SECURITY
134    
135 root 1.10 ./configure --enable-hmac-length=16 --enable-rand-length=16 --enable-digest=sha384
136 pcg 1.1
137     This uses a 16 byte HMAC checksum to authenticate packets (I guess 8-12
138     would also be pretty secure ;) and will additionally prefix each packet
139 root 1.10 with 16 bytes of random data.
140 pcg 1.1
141 pcg 1.8 In general, remember that AES-128 seems to be as secure but faster than
142 pcg 1.1 AES-192 or AES-256, more randomness helps against sniffing and a longer
143 pcg 1.8 HMAC helps against spoofing. MD4 is a fast digest, SHA1, RIPEMD160, SHA256
144     are consecutively better, and Blowfish is a fast cipher (and also quite
145     secure).
146 pcg 1.1
147     =head1 HOW TO SET UP A SIMPLE VPN
148    
149     In this section I will describe how to get a simple VPN consisting of
150     three hosts up and running.
151    
152     =head2 STEP 1: configuration
153    
154 pcg 1.8 First you have to create a daemon configuration file and put it into the
155 pcg 1.1 configuration directory. This is usually C</etc/gvpe>, depending on how you
156 pcg 1.8 configured gvpe, and can be overwritten using the C<-c> command line switch.
157 pcg 1.1
158     Put the following lines into C</etc/gvpe/gvpe.conf>:
159    
160     udp-port = 50000 # the external port to listen on (configure your firewall)
161     mtu = 1400 # minimum MTU of all outgoing interfaces on all hosts
162     ifname = vpn0 # the local network device name
163    
164     node = first # just a nickname
165     hostname = first.example.net # the DNS name or IP address of the host
166    
167     node = second
168     hostname = 133.55.82.9
169    
170     node = third
171     hostname = third.example.net
172    
173 pcg 1.8 The only other file necessary is the C<if-up> script that initializes the
174     virtual ethernet interface on the local host. Put the following lines into
175     C</etc/gvpe/if-up> and make it executable (C<chmod 755 /etc/gvpe/if-up>):
176 pcg 1.1
177     #!/bin/sh
178     ip link set $IFNAME address $MAC mtu $MTU up
179     [ $NODENAME = first ] && ip addr add 10.0.1.1 dev $IFNAME
180     [ $NODENAME = second ] && ip addr add 10.0.2.1 dev $IFNAME
181     [ $NODENAME = third ] && ip addr add 10.0.3.1 dev $IFNAME
182     ip route add 10.0.0.0/16 dev $IFNAME
183    
184     This script will give each node a different IP address in the C<10.0/16>
185 pcg 1.8 network. The internal network (if gvpe runs on a router) should then be
186 pcg 1.1 set to a subset of that network, e.g. C<10.0.1.0/24> on node C<first>,
187     C<10.0.2.0/24> on node C<second>, and so on.
188    
189     By enabling routing on the gateway host that runs C<gvpe> all nodes will
190 pcg 1.8 be able to reach the other nodes. You can, of course, also use proxy ARP
191     or other means of pseudo-bridging, or (best) full routing - the choice is
192     yours.
193 pcg 1.1
194     =head2 STEP 2: create the RSA key pairs for all hosts
195    
196 pcg 1.8 Run the following command to generate all key pairs for all nodes (that
197     might take a while):
198 pcg 1.1
199     gvpectrl -c /etc/gvpe -g
200    
201     This command will put the public keys into C<<
202     /etc/gvpe/pubkeys/I<nodename> >> and the private keys into C<<
203     /etc/gvpe/hostkeys/I<nodename> >>.
204    
205     =head2 STEP 3: distribute the config files to all nodes
206    
207 pcg 1.8 Now distribute the config files and private keys to the other nodes. This
208     should be done in two steps, since only the private keys meant for a node
209     should be distributed (so each node has only it's own private key).
210    
211     The example uses rsync-over-ssh
212 pcg 1.1
213     First all the config files without the hostkeys should be distributed:
214    
215     rsync -avzessh /etc/gvpe first.example.net:/etc/. --exclude hostkeys
216     rsync -avzessh /etc/gvpe 133.55.82.9:/etc/. --exclude hostkeys
217     rsync -avzessh /etc/gvpe third.example.net:/etc/. --exclude hostkeys
218    
219     Then the hostkeys should be copied:
220    
221     rsync -avzessh /etc/gvpe/hostkeys/first first.example.net:/etc/hostkey
222     rsync -avzessh /etc/gvpe/hostkeys/second 133.55.82.9:/etc/hostkey
223     rsync -avzessh /etc/gvpe/hostkeys/third third.example.net:/etc/hostkey
224    
225 pcg 1.8 You should now check the configuration by issuing the command C<gvpectrl -c
226 pcg 1.1 /etc/gvpe -s> on each node and verify it's output.
227    
228     =head2 STEP 4: starting gvpe
229    
230     You should then start gvpe on each node by issuing a command like:
231    
232 pcg 1.8 gvpe -D -l info first # first is the nodename
233 pcg 1.1
234 pcg 1.8 This will make the gvpe daemon stay in foreground. You should then see
235 pcg 1.1 "connection established" messages. If you don't see them check your
236     firewall and routing (use tcpdump ;).
237    
238     If this works you should check your networking setup by pinging various
239     endpoints.
240    
241 pcg 1.8 To make gvpe run more permanently you can either run it as a daemon (by
242     starting it without the C<-D> switch), or, much better, from your inittab
243     or equivalent. I use a line like this on all my systems:
244 pcg 1.1
245     t1:2345:respawn:/opt/gvpe/sbin/gvpe -D -L first >/dev/null 2>&1
246    
247     =head2 STEP 5: enjoy
248    
249     ... and play around. Sending a -HUP (C<gvpectrl -kHUP>) to the daemon
250     will make it try to connect to all other nodes again. If you run it from
251     inittab, as is recommended, C<gvpectrl -k> (or simply C<killall gvpe>) will
252     kill the daemon, start it again, making it read it's configuration files
253     again.
254    
255     =head1 SEE ALSO
256    
257 pcg 1.8 gvpe.osdep(5) for OS-dependent information, gvpe.conf(5), gvpectrl(8),
258 pcg 1.6 and for a description of the transports, protocol, and routing algorithm,
259     gvpe.protocol(7).
260 pcg 1.1
261 pcg 1.8 The GVPE mailing list, at L<http://lists.schmorp.de/>, or
262 pcg 1.7 C<gvpe@lists.schmorp.de>.
263    
264 pcg 1.1 =head1 AUTHOR
265    
266 pcg 1.7 Marc Lehmann <gvpe@schmorp.de>
267 pcg 1.1
268     =head1 COPYRIGHTS AND LICENSES
269    
270     GVPE itself is distributed under the GENERAL PUBLIC LICENSE (see the file
271     COPYING that should be part of your distribution).
272    
273     In some configurations it uses modified versions of the tinc vpn suite,
274     which is also available under the GENERAL PUBLIC LICENSE.
275