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Revision: 1.9
Committed: Mon Sep 1 06:06:11 2008 UTC (16 years, 1 month ago) by pcg
Branch: MAIN
CVS Tags: rel-2_21, rel-2_22
Changes since 1.8: +3 -3 lines
Log Message:
*** empty log message ***

File Contents

# 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     =over 4
56    
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     ./configure --enable-hmac-length=16 --enable-rand-length=8 --enable-digest=sha1
136    
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 pcg 1.2 with 8 bytes of random data. In the long run, people should move to
140 pcg 1.8 SHA-256 and beyond).
141 pcg 1.1
142 pcg 1.8 In general, remember that AES-128 seems to be as secure but faster than
143 pcg 1.1 AES-192 or AES-256, more randomness helps against sniffing and a longer
144 pcg 1.8 HMAC helps against spoofing. MD4 is a fast digest, SHA1, RIPEMD160, SHA256
145     are consecutively better, and Blowfish is a fast cipher (and also quite
146     secure).
147 pcg 1.1
148     =head1 HOW TO SET UP A SIMPLE VPN
149    
150     In this section I will describe how to get a simple VPN consisting of
151     three hosts up and running.
152    
153     =head2 STEP 1: configuration
154    
155 pcg 1.8 First you have to create a daemon configuration file and put it into the
156 pcg 1.1 configuration directory. This is usually C</etc/gvpe>, depending on how you
157 pcg 1.8 configured gvpe, and can be overwritten using the C<-c> command line switch.
158 pcg 1.1
159     Put the following lines into C</etc/gvpe/gvpe.conf>:
160    
161     udp-port = 50000 # the external port to listen on (configure your firewall)
162     mtu = 1400 # minimum MTU of all outgoing interfaces on all hosts
163     ifname = vpn0 # the local network device name
164    
165     node = first # just a nickname
166     hostname = first.example.net # the DNS name or IP address of the host
167    
168     node = second
169     hostname = 133.55.82.9
170    
171     node = third
172     hostname = third.example.net
173    
174 pcg 1.8 The only other file necessary is the C<if-up> script that initializes the
175     virtual ethernet interface on the local host. Put the following lines into
176     C</etc/gvpe/if-up> and make it executable (C<chmod 755 /etc/gvpe/if-up>):
177 pcg 1.1
178     #!/bin/sh
179     ip link set $IFNAME address $MAC mtu $MTU up
180     [ $NODENAME = first ] && ip addr add 10.0.1.1 dev $IFNAME
181     [ $NODENAME = second ] && ip addr add 10.0.2.1 dev $IFNAME
182     [ $NODENAME = third ] && ip addr add 10.0.3.1 dev $IFNAME
183     ip route add 10.0.0.0/16 dev $IFNAME
184    
185     This script will give each node a different IP address in the C<10.0/16>
186 pcg 1.8 network. The internal network (if gvpe runs on a router) should then be
187 pcg 1.1 set to a subset of that network, e.g. C<10.0.1.0/24> on node C<first>,
188     C<10.0.2.0/24> on node C<second>, and so on.
189    
190     By enabling routing on the gateway host that runs C<gvpe> all nodes will
191 pcg 1.8 be able to reach the other nodes. You can, of course, also use proxy ARP
192     or other means of pseudo-bridging, or (best) full routing - the choice is
193     yours.
194 pcg 1.1
195     =head2 STEP 2: create the RSA key pairs for all hosts
196    
197 pcg 1.8 Run the following command to generate all key pairs for all nodes (that
198     might take a while):
199 pcg 1.1
200     gvpectrl -c /etc/gvpe -g
201    
202     This command will put the public keys into C<<
203     /etc/gvpe/pubkeys/I<nodename> >> and the private keys into C<<
204     /etc/gvpe/hostkeys/I<nodename> >>.
205    
206     =head2 STEP 3: distribute the config files to all nodes
207    
208 pcg 1.8 Now distribute the config files and private keys to the other nodes. This
209     should be done in two steps, since only the private keys meant for a node
210     should be distributed (so each node has only it's own private key).
211    
212     The example uses rsync-over-ssh
213 pcg 1.1
214     First all the config files without the hostkeys should be distributed:
215    
216     rsync -avzessh /etc/gvpe first.example.net:/etc/. --exclude hostkeys
217     rsync -avzessh /etc/gvpe 133.55.82.9:/etc/. --exclude hostkeys
218     rsync -avzessh /etc/gvpe third.example.net:/etc/. --exclude hostkeys
219    
220     Then the hostkeys should be copied:
221    
222     rsync -avzessh /etc/gvpe/hostkeys/first first.example.net:/etc/hostkey
223     rsync -avzessh /etc/gvpe/hostkeys/second 133.55.82.9:/etc/hostkey
224     rsync -avzessh /etc/gvpe/hostkeys/third third.example.net:/etc/hostkey
225    
226 pcg 1.8 You should now check the configuration by issuing the command C<gvpectrl -c
227 pcg 1.1 /etc/gvpe -s> on each node and verify it's output.
228    
229     =head2 STEP 4: starting gvpe
230    
231     You should then start gvpe on each node by issuing a command like:
232    
233 pcg 1.8 gvpe -D -l info first # first is the nodename
234 pcg 1.1
235 pcg 1.8 This will make the gvpe daemon stay in foreground. You should then see
236 pcg 1.1 "connection established" messages. If you don't see them check your
237     firewall and routing (use tcpdump ;).
238    
239     If this works you should check your networking setup by pinging various
240     endpoints.
241    
242 pcg 1.8 To make gvpe run more permanently you can either run it as a daemon (by
243     starting it without the C<-D> switch), or, much better, from your inittab
244     or equivalent. I use a line like this on all my systems:
245 pcg 1.1
246     t1:2345:respawn:/opt/gvpe/sbin/gvpe -D -L first >/dev/null 2>&1
247    
248     =head2 STEP 5: enjoy
249    
250     ... and play around. Sending a -HUP (C<gvpectrl -kHUP>) to the daemon
251     will make it try to connect to all other nodes again. If you run it from
252     inittab, as is recommended, C<gvpectrl -k> (or simply C<killall gvpe>) will
253     kill the daemon, start it again, making it read it's configuration files
254     again.
255    
256     =head1 SEE ALSO
257    
258 pcg 1.8 gvpe.osdep(5) for OS-dependent information, gvpe.conf(5), gvpectrl(8),
259 pcg 1.6 and for a description of the transports, protocol, and routing algorithm,
260     gvpe.protocol(7).
261 pcg 1.1
262 pcg 1.8 The GVPE mailing list, at L<http://lists.schmorp.de/>, or
263 pcg 1.7 C<gvpe@lists.schmorp.de>.
264    
265 pcg 1.1 =head1 AUTHOR
266    
267 pcg 1.7 Marc Lehmann <gvpe@schmorp.de>
268 pcg 1.1
269     =head1 COPYRIGHTS AND LICENSES
270    
271     GVPE itself is distributed under the GENERAL PUBLIC LICENSE (see the file
272     COPYING that should be part of your distribution).
273    
274     In some configurations it uses modified versions of the tinc vpn suite,
275     which is also available under the GENERAL PUBLIC LICENSE.
276