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Revision: 1.8
Committed: Fri Mar 18 01:53:05 2005 UTC (19 years, 8 months ago) by pcg
Branch: MAIN
CVS Tags: rel-1_9, rel-1_8, rel-2_01, rel-3_0, rel-2_2, rel-2_0, rel-2_21, rel-2_22, rel-2_25, HEAD
Changes since 1.7: +59 -45 lines
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File Contents

# Content
1
2 ==== NAME ====
3
4 GNU-VPE - Overview of the GNU Virtual Private Ethernet suite.
5
6
7 ==== DESCRIPTION ====
8
9 GVPE is a suite designed to provide a virtual private network for
10 multiple nodes over an untrusted network. This document first gives an
11 introduction to VPNs in general and then describes the specific
12 implementation of GVPE.
13
14
15 == WHAT IS A VPN? ==
16
17 VPN is an acronym, it stands for:
18
19 : Virtual means that no physical network is created (of course), but a
20 network is *emulated* by creating multiple tunnels between the
21 member nodes by encapsulating and sending data over another
22 transport network.
23
24 Usually the emulated network is a normal IP or Ethernet, and the
25 transport network is the Internet. However, using a VPN system like
26 GVPE to connect nodes over other untrusted networks such as Wireless
27 LAN is not uncommon.
28
29 : Private means that non-participating nodes cannot decode ("sniff)"
30 nor inject ("spoof") packets. This means that nodes can be connected
31 over untrusted networks such as the public Internet without fear of
32 being eavesdropped while at the same time being able to trust data
33 sent by other nodes.
34
35 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
39 : Network means that more than two parties can participate in the
40 network, so for instance it's possible to connect multiple branches
41 of a company into a single network. Many so-called "vpn" solutions
42 only create point-to-point tunnels, which in turn can be used to
43 build larger networks.
44
45 GVPE provides a true multi-point network in wich any number of nodes
46 (at least a few dozen in practise, the theoretical limit is 4095
47 nodes) can participate.
48
49
50 == GVPE DESIGN GOALS ==
51
52 : SIMPLE DESIGN
53 Cipher, HMAC algorithms and other key parameters must be selected at
54 compile time - this makes it possible to only link in algorithms you
55 actually need. It also makes the crypto part of the source very
56 transparent and easy to inspect, and last not least this makes it
57 possible to hardcode the layout of all packets into the binary. GVPE
58 goes a step further and internally reserves blocks of the same
59 length for all packets, which virtually removes all possibilities of
60 buffer overflows, as there is only a single type of buffer and it's
61 always of fixed length.
62
63 : EASY TO SETUP
64 A few lines of config (the config file is shared unmodified between
65 all hosts) and a single run of ``gvpectrl'' to generate the keys
66 suffices to make it work.
67
68 : MAC-BASED SECURITY
69 Since every host has it's own private key, other hosts cannot spoof
70 traffic from this host. That makes it possible to filter packet by
71 MAC address, e.g. to ensure that packets from a specific IP address
72 come, in fact, from a specific host that is associated with that IP
73 and not from another host.
74
75
76 ==== PROGRAMS ====
77
78 Vpe comes with two programs: one daemon (``gvpe'') and one control
79 program (``gvpectrl'').
80
81 : gvpectrl
82 Is used to generate the keys, check and give an overview of of the
83 configuration and contorl the daemon (restarting etc.).
84
85 : gvpe
86 Is the daemon used to establish and maintain connections to the
87 other network members. It should be run on the gateway machine.
88
89
90 ==== COMPILETIME CONFIGURATION ====
91
92 Please have a look at the ``gvpe.osdep(5)'' manpage for
93 platform-specific information.
94
95 Here are a few recipes for compiling your gvpe, showing the extremes
96 (fast, small, insecure OR slow, large, more secure), between you should
97 choose:
98
99
100 == AS LOW PACKET OVERHEAD AS POSSIBLE ==
101
102 ./configure --enable-hmac-length=4 --enable-rand-length=0
103
104 Minimize the header overhead of VPN packets (the above will result in
105 only 4 bytes of overhead over the raw ethernet frame). This is a
106 insecure configuration because a HMAC length of 4 makes collision
107 attacks based on the birthday paradox easy, though.
108
109
110 == MINIMIZE CPU TIME REQUIRED ==
111
112 ./configure --enable-cipher=bf --enable-digest=md4
113
114 Use the fastest cipher and digest algorithms currently available in
115 gvpe. MD4 has been broken and is quite insecure, though.
116
117
118 == MAXIMIZE SECURITY ==
119
120 ./configure --enable-hmac-length=16 --enable-rand-length=8 --enable-digest=sha1
121
122 This uses a 16 byte HMAC checksum to authenticate packets (I guess 8-12
123 would also be pretty secure ;) and will additionally prefix each packet
124 with 8 bytes of random data. In the long run, people should move to
125 SHA-224 and beyond, but support in openssl is missing as of writing this
126 document.
127
128 In general, remember that AES-128 seems to be more secure and faster
129 than AES-192 or AES-256, more randomness helps against sniffing and a
130 longer HMAC helps against spoofing. MD4 is a fast digest, SHA1 or
131 RIPEMD160 are better, and Blowfish is a fast cipher (and also quite
132 secure).
133
134
135 ==== HOW TO SET UP A SIMPLE VPN ====
136
137 In this section I will describe how to get a simple VPN consisting of
138 three hosts up and running.
139
140
141 == STEP 1: configuration ==
142
143 First you have to create a daemon configuation file and put it into the
144 configuration directory. This is usually ``/etc/gvpe'', depending on how
145 you configured gvpe, and can be overwritten using the ``-c'' commandline
146 switch.
147
148 Put the following lines into ``/etc/gvpe/gvpe.conf'':
149
150 udp-port = 50000 # the external port to listen on (configure your firewall)
151 mtu = 1400 # minimum MTU of all outgoing interfaces on all hosts
152 ifname = vpn0 # the local network device name
153
154 node = first # just a nickname
155 hostname = first.example.net # the DNS name or IP address of the host
156
157 node = second
158 hostname = 133.55.82.9
159
160 node = third
161 hostname = third.example.net
162
163 The only other file neccessary if the ``if-up'' script that initializes
164 the local ethernet interface. Put the following lines into
165 ``/etc/gvpe/if-up'' and make it execute (``chmod 755 /etc/gvpe/if-up''):
166
167 #!/bin/sh
168 ip link set $IFNAME address $MAC mtu $MTU up
169 [ $NODENAME = first ] && ip addr add 10.0.1.1 dev $IFNAME
170 [ $NODENAME = second ] && ip addr add 10.0.2.1 dev $IFNAME
171 [ $NODENAME = third ] && ip addr add 10.0.3.1 dev $IFNAME
172 ip route add 10.0.0.0/16 dev $IFNAME
173
174 This script will give each node a different IP address in the
175 ``10.0/16'' network. The internal network (e.g. the ``eth0'' interface)
176 should then be set to a subset of that network, e.g. ``10.0.1.0/24'' on
177 node ``first'', ``10.0.2.0/24'' on node ``second'', and so on.
178
179 By enabling routing on the gateway host that runs ``gvpe'' all nodes
180 will be able to reach the other nodes. You can, of course, also use
181 proxy arp or other means of pseudo-bridging (or even real briding), or
182 (best) full routing - the choice is yours.
183
184
185 == STEP 2: create the RSA key pairs for all hosts ==
186
187 Run the following command to generate all key pairs (that might take a
188 while):
189
190 gvpectrl -c /etc/gvpe -g
191
192 This command will put the public keys into
193 ``/etc/gvpe/pubkeys/*nodename*'' and the private keys into
194 ``/etc/gvpe/hostkeys/*nodename*''.
195
196
197 == STEP 3: distribute the config files to all nodes ==
198
199 Now distribute the config files to the other nodes. This should be done
200 in two steps, since the private keys should not be distributed. The
201 example uses rsync-over-ssh
202
203 First all the config files without the hostkeys should be distributed:
204
205 rsync -avzessh /etc/gvpe first.example.net:/etc/. --exclude hostkeys
206 rsync -avzessh /etc/gvpe 133.55.82.9:/etc/. --exclude hostkeys
207 rsync -avzessh /etc/gvpe third.example.net:/etc/. --exclude hostkeys
208
209 Then the hostkeys should be copied:
210
211 rsync -avzessh /etc/gvpe/hostkeys/first first.example.net:/etc/hostkey
212 rsync -avzessh /etc/gvpe/hostkeys/second 133.55.82.9:/etc/hostkey
213 rsync -avzessh /etc/gvpe/hostkeys/third third.example.net:/etc/hostkey
214
215 You should now check the configration by issuing the command ``gvpectrl
216 -c /etc/gvpe -s'' on each node and verify it's output.
217
218
219 == STEP 4: starting gvpe ==
220
221 You should then start gvpe on each node by issuing a command like:
222
223 gvpe -D -linfo first # first is the nodename
224
225 This will make the gvpe stay in foreground. You should then see
226 "connection established" messages. If you don't see them check your
227 firewall and routing (use tcpdump ;).
228
229 If this works you should check your networking setup by pinging various
230 endpoints.
231
232 To make gvpe run more permanently you can either run it as a daemon (by
233 starting it without the ``-D'' switch), or, much better, from your
234 inittab. I use a line like this on my systems:
235
236 t1:2345:respawn:/opt/gvpe/sbin/gvpe -D -L first >/dev/null 2>&1
237
238
239 == STEP 5: enjoy ==
240
241 ... and play around. Sending a -HUP (``gvpectrl -kHUP'') to the daemon
242 will make it try to connect to all other nodes again. If you run it from
243 inittab, as is recommended, ``gvpectrl -k'' (or simply ``killall gvpe'')
244 will kill the daemon, start it again, making it read it's configuration
245 files again.
246
247
248 ==== SEE ALSO ====
249
250 gvpe.osdep(5) for OS-depedendent information, gvpe.conf(5), gvpectrl(8),
251 and for a description of the transports, protocol, and routing
252 algorithm, gvpe.protocol(7).
253
254 The GVPE mailinglist, at <http://lists.schmorp.de/>, or
255 ``gvpe@lists.schmorp.de''.
256
257
258 ==== AUTHOR ====
259
260 Marc Lehmann <gvpe@schmorp.de>
261
262
263 ==== COPYRIGHTS AND LICENSES ====
264
265 GVPE itself is distributed under the GENERAL PUBLIC LICENSE (see the
266 file COPYING that should be part of your distribution).
267
268 In some configurations it uses modified versions of the tinc vpn suite,
269 which is also available under the GENERAL PUBLIC LICENSE.
270