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Revision: 1.14
Committed: Wed Nov 2 07:06:38 2016 UTC (7 years, 6 months ago) by root
Branch: MAIN
CVS Tags: rel-3_0, HEAD
Changes since 1.13: +60 -29 lines
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File Contents

# Content
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133 .\" ========================================================================
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135 .IX Title "GVPE 5"
136 .TH GVPE 5 "2016-11-02" "2.25" "GNU Virtual Private Ethernet"
137 .\" For nroff, turn off justification. Always turn off hyphenation; it makes
138 .\" way too many mistakes in technical documents.
139 .if n .ad l
140 .nh
141 .SH "NAME"
142 GNU\-VPE \- Overview of the GNU Virtual Private Ethernet suite.
143 .SH "DESCRIPTION"
144 .IX Header "DESCRIPTION"
145 \&\s-1GVPE\s0 is a suite designed to provide a virtual private network for multiple
146 nodes over an untrusted network. This document first gives an introduction
147 to VPNs in general and then describes the specific implementation of \s-1GVPE.\s0
148 .SS "\s-1WHAT IS A VPN\s0?"
149 .IX Subsection "WHAT IS A VPN?"
150 \&\s-1VPN\s0 is an acronym, it stands for:
151 .IP "Virtual" 4
152 .IX Item "Virtual"
153 Virtual means that no physical network is created (of course), but a
154 network is \fIemulated\fR by creating multiple tunnels between the member
155 nodes by encapsulating and sending data over another transport network.
156 .Sp
157 Usually the emulated network is a normal \s-1IP\s0 or Ethernet, and the transport
158 network is the Internet. However, using a \s-1VPN\s0 system like \s-1GVPE\s0 to connect
159 nodes over other untrusted networks such as Wireless \s-1LAN\s0 is not uncommon.
160 .IP "Private" 4
161 .IX Item "Private"
162 Private means that non-participating nodes cannot decode (\*(L"sniff)\*(R" nor
163 inject (\*(L"spoof\*(R") packets. This means that nodes can be connected over
164 untrusted networks such as the public Internet without fear of being
165 eavesdropped while at the same time being able to trust data sent by other
166 nodes.
167 .Sp
168 In the case of \s-1GVPE,\s0 even participating nodes cannot sniff packets
169 send to other nodes or spoof packets as if sent from other nodes, so
170 communications between any two nodes is private to those two nodes.
171 .IP "Network" 4
172 .IX Item "Network"
173 Network means that more than two parties can participate in the network,
174 so for instance it's possible to connect multiple branches of a company
175 into a single network. Many so-called \*(L"\s-1VPN\*(R"\s0 solutions only create
176 point-to-point tunnels, which in turn can be used to build larger
177 networks.
178 .Sp
179 \&\s-1GVPE\s0 provides a true multi-point network in which any number of nodes (at
180 least a few dozen in practise, the theoretical limit is 4095 nodes) can
181 participate.
182 .SS "\s-1GVPE DESIGN GOALS\s0"
183 .IX Subsection "GVPE DESIGN GOALS"
184 .IP "\s-1SIMPLE DESIGN\s0" 4
185 .IX Item "SIMPLE DESIGN"
186 Cipher, \s-1HMAC\s0 algorithms and other key parameters must be selected
187 at compile time \- this makes it possible to only link in algorithms
188 you actually need. It also makes the crypto part of the source very
189 transparent and easy to inspect, and last not least this makes it possible
190 to hardcode the layout of all packets into the binary. \s-1GVPE\s0 goes a step
191 further and internally reserves blocks of the same length for all packets,
192 which virtually removes all possibilities of buffer overflows, as there is
193 only a single type of buffer and it's always of fixed length.
194 .IP "\s-1EASY TO SETUP\s0" 4
195 .IX Item "EASY TO SETUP"
196 A few lines of config (the config file is shared unmodified between all
197 hosts) and generating an \s-1RSA\s0 key-pair on each node suffices to make it
198 work.
199 .IP "MAC-BASED \s-1SECURITY\s0" 4
200 .IX Item "MAC-BASED SECURITY"
201 Since every host has it's own private key, other hosts cannot spoof
202 traffic from this host. That makes it possible to filter packet by \s-1MAC\s0
203 address, e.g. to ensure that packets from a specific \s-1IP\s0 address come, in
204 fact, from a specific host that is associated with that \s-1IP\s0 and not from
205 another host.
206 .SH "PROGRAMS"
207 .IX Header "PROGRAMS"
208 Gvpe comes with two programs: one daemon (\f(CW\*(C`gvpe\*(C'\fR) and one control program
209 (\f(CW\*(C`gvpectrl\*(C'\fR).
210 .IP "gvpectrl" 4
211 .IX Item "gvpectrl"
212 This program is used to generate the keys, check and give an overview of of the
213 configuration and to control the daemon (restarting etc.).
214 .IP "gvpe" 4
215 .IX Item "gvpe"
216 This is the daemon used to establish and maintain connections to the other
217 network nodes. It should be run on the gateway of each \s-1VPN\s0 subnet.
218 .SH "COMPILETIME CONFIGURATION"
219 .IX Header "COMPILETIME CONFIGURATION"
220 Please have a look at the \f(CW\*(C`gvpe.osdep(5)\*(C'\fR manpage for platform-specific
221 information.
222 .PP
223 Gvpe hardcodes most encryption parameters. While this reduces flexibility,
224 it makes the program much simpler and helps making buffer overflows
225 impossible under most circumstances.
226 .PP
227 Here are a few recipes for compiling your gvpe, showing the extremes
228 (fast, small, insecure \s-1OR\s0 slow, large, more secure), between which you
229 should choose:
230 .SS "\s-1AS LOW PACKET OVERHEAD AS POSSIBLE\s0"
231 .IX Subsection "AS LOW PACKET OVERHEAD AS POSSIBLE"
232 .Vb 1
233 \& ./configure \-\-enable\-hmac\-length=4 \-\-enable\-rand\-length=0
234 .Ve
235 .PP
236 Minimize the header overhead of \s-1VPN\s0 packets (the above will result in
237 only 4 bytes of overhead over the raw ethernet frame). This is a insecure
238 configuration because a \s-1HMAC\s0 length of 4 makes collision attacks almost
239 trivial.
240 .SS "\s-1MINIMIZE CPU TIME REQUIRED\s0"
241 .IX Subsection "MINIMIZE CPU TIME REQUIRED"
242 .Vb 1
243 \& ./configure \-\-enable\-cipher=bf \-\-enable\-digest=md4
244 .Ve
245 .PP
246 Use the fastest cipher and digest algorithms currently available in
247 gvpe. \s-1MD4\s0 has been broken and is quite insecure, though, so using another
248 digest algorithm is recommended.
249 .SS "\s-1MAXIMIZE SECURITY\s0"
250 .IX Subsection "MAXIMIZE SECURITY"
251 .Vb 1
252 \& ./configure \-\-enable\-hmac\-length=16 \-\-enable\-rand\-length=12 \-\-enable\-digest=ripemd610
253 .Ve
254 .PP
255 This uses a 16 byte \s-1HMAC\s0 checksum to authenticate packets (I guess 8\-12
256 would also be pretty secure ;) and will additionally prefix each packet
257 with 12 bytes of random data.
258 .PP
259 In general, remember that \s-1AES\-128\s0 seems to be as secure but faster than
260 \&\s-1AES\-192\s0 or \s-1AES\-256,\s0 more randomness helps against sniffing and a longer
261 \&\s-1HMAC\s0 helps against spoofing. \s-1MD4\s0 is a fast digest, \s-1SHA1, RIPEMD160, SHA256\s0
262 are consecutively better, and Blowfish is a fast cipher (and also quite
263 secure).
264 .SH "HOW TO SET UP A SIMPLE VPN"
265 .IX Header "HOW TO SET UP A SIMPLE VPN"
266 In this section I will describe how to get a simple \s-1VPN\s0 consisting of
267 three hosts up and running.
268 .SS "\s-1STEP 1:\s0 configuration"
269 .IX Subsection "STEP 1: configuration"
270 First you have to create a daemon configuration file and put it into the
271 configuration directory. This is usually \f(CW\*(C`/etc/gvpe\*(C'\fR, depending on how you
272 configured gvpe, and can be overwritten using the \f(CW\*(C`\-c\*(C'\fR command line switch.
273 .PP
274 Put the following lines into \f(CW\*(C`/etc/gvpe/gvpe.conf\*(C'\fR:
275 .PP
276 .Vb 3
277 \& udp\-port = 50000 # the external port to listen on (configure your firewall)
278 \& mtu = 1400 # minimum MTU of all outgoing interfaces on all hosts
279 \& ifname = vpn0 # the local network device name
280 \&
281 \& node = first # just a nickname
282 \& hostname = first.example.net # the DNS name or IP address of the host
283 \&
284 \& node = second
285 \& hostname = 133.55.82.9
286 \&
287 \& node = third
288 \& hostname = third.example.net
289 .Ve
290 .PP
291 The only other file necessary is the \f(CW\*(C`if\-up\*(C'\fR script that initializes the
292 virtual ethernet interface on the local host. Put the following lines into
293 \&\f(CW\*(C`/etc/gvpe/if\-up\*(C'\fR and make it executable (\f(CW\*(C`chmod 755 /etc/gvpe/if\-up\*(C'\fR):
294 .PP
295 .Vb 6
296 \& #!/bin/sh
297 \& ip link set $IFNAME address $MAC mtu $MTU up
298 \& [ $NODENAME = first ] && ip addr add 10.0.1.1 dev $IFNAME
299 \& [ $NODENAME = second ] && ip addr add 10.0.2.1 dev $IFNAME
300 \& [ $NODENAME = third ] && ip addr add 10.0.3.1 dev $IFNAME
301 \& ip route add 10.0.0.0/16 dev $IFNAME
302 .Ve
303 .PP
304 This script will give each node a different \s-1IP\s0 address in the \f(CW\*(C`10.0/16\*(C'\fR
305 network. The internal network (if gvpe runs on a router) should then be
306 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,
307 \&\f(CW\*(C`10.0.2.0/24\*(C'\fR on node \f(CW\*(C`second\*(C'\fR, and so on.
308 .PP
309 By enabling routing on the gateway host that runs \f(CW\*(C`gvpe\*(C'\fR all nodes will
310 be able to reach the other nodes. You can, of course, also use proxy \s-1ARP\s0
311 or other means of pseudo-bridging, or (best) full routing \- the choice is
312 yours.
313 .SS "\s-1STEP 2:\s0 create the \s-1RSA\s0 key pair for each node"
314 .IX Subsection "STEP 2: create the RSA key pair for each node"
315 Next you have to generate the \s-1RSA\s0 keys for the nodes. While you can set
316 up \s-1GVPE\s0 so you can generate all keys on a single host and centrally
317 distribute all keys, it is safer to generate the key for each node on the
318 node, so that the secret/private key does not have to be copied over the
319 network.
320 .PP
321 To do so, run the following command to generate a key pair:
322 .PP
323 .Vb 1
324 \& gvpectrl \-c /etc/gvpe \-g nodekey
325 .Ve
326 .PP
327 This will create two files, \fInodekey\fR and \fInodekey.privkey\fR. The former
328 should be copied to \fI/etc/gvpe/pubkey/\fInodename\fI\fR on the host where
329 your config file is (you will have to create the \fIpubkey\fR directory
330 first):
331 .PP
332 .Vb 1
333 \& scp nodekey confighost:/etc/gvpe/pubkey/nodename
334 .Ve
335 .PP
336 The private key \fInodekey.privkey\fR should be moved to \fI/etc/gvpe/hostkey\fR:
337 .PP
338 .Vb 2
339 \& mkdir \-p /etc/gvpe
340 \& mv nodekey.privkey /etc/gvpe/hostkey
341 .Ve
342 .SS "\s-1STEP 3:\s0 distribute the config files to all nodes"
343 .IX Subsection "STEP 3: distribute the config files to all nodes"
344 Now distribute the config files and public keys to the other nodes.
345 .PP
346 The example uses rsync-over-ssh to copy the config file and all the public
347 keys:
348 .PP
349 .Vb 3
350 \& rsync \-avzessh /etc/gvpe first.example.net:/etc/. \-\-exclude hostkey
351 \& rsync \-avzessh /etc/gvpe 133.55.82.9:/etc/. \-\-exclude hostkey
352 \& rsync \-avzessh /etc/gvpe third.example.net:/etc/. \-\-exclude hostkey
353 .Ve
354 .PP
355 You should now check the configuration by issuing the command \f(CW\*(C`gvpectrl
356 \&\-c /etc/gvpe \-s\*(C'\fR on each node and verify it's output.
357 .SS "\s-1STEP 4:\s0 starting gvpe"
358 .IX Subsection "STEP 4: starting gvpe"
359 You should then start gvpe on each node by issuing a command like:
360 .PP
361 .Vb 1
362 \& gvpe \-D \-l info first # first is the nodename
363 .Ve
364 .PP
365 This will make the gvpe daemon stay in foreground. You should then see
366 \&\*(L"connection established\*(R" messages. If you don't see them check your
367 firewall and routing (use tcpdump ;).
368 .PP
369 If this works you should check your networking setup by pinging various
370 endpoints.
371 .PP
372 To make gvpe run more permanently you can either run it as a daemon (by
373 starting it without the \f(CW\*(C`\-D\*(C'\fR switch), or, much better, from your inittab
374 or equivalent. I use a line like this on all my systems:
375 .PP
376 .Vb 1
377 \& t1:2345:respawn:/opt/gvpe/sbin/gvpe \-D \-L first >/dev/null 2>&1
378 .Ve
379 .SS "\s-1STEP 5:\s0 enjoy"
380 .IX Subsection "STEP 5: enjoy"
381 \&... and play around. Sending a \-HUP (\f(CW\*(C`gvpectrl \-kHUP\*(C'\fR) to the daemon
382 will make it try to connect to all other nodes again. If you run it from
383 inittab \f(CW\*(C`gvpectrl \-k\*(C'\fR (or simply \f(CW\*(C`killall gvpe\*(C'\fR) will kill the daemon,
384 start it again, making it read it's configuration files again.
385 .PP
386 To run the \s-1GVPE\s0 daemon permanently from your SysV init, you can add it to
387 your \fIinittab\fR, e.g.:
388 .PP
389 .Vb 1
390 \& t1:2345:respawn:/bin/sh \-c "exec nice \-n\-20 /path/to/gvpe \-D node >/var/log/gvpe.log 2>&1"
391 .Ve
392 .PP
393 For systems using systemd, you can use a unit file similar to this one:
394 .PP
395 .Vb 4
396 \& [Unit]
397 \& Description=gvpe
398 \& After=network.target
399 \& Before=remote\-fs.target
400 \&
401 \& [Service]
402 \& ExecStart=/path/to/gvpe \-D node
403 \& KillMode=process
404 \& Restart=always
405 \&
406 \& [Install]
407 \& WantedBy=multi\-user.target
408 .Ve
409 .SH "SEE ALSO"
410 .IX Header "SEE ALSO"
411 \&\fIgvpe.osdep\fR\|(5) for OS-dependent information, \fIgvpe.conf\fR\|(5), \fIgvpectrl\fR\|(8),
412 and for a description of the transports, protocol, and routing algorithm,
413 \&\fIgvpe.protocol\fR\|(7).
414 .PP
415 The \s-1GVPE\s0 mailing list, at <http://lists.schmorp.de/>, or
416 \&\f(CW\*(C`gvpe@lists.schmorp.de\*(C'\fR.
417 .SH "AUTHOR"
418 .IX Header "AUTHOR"
419 Marc Lehmann <gvpe@schmorp.de>
420 .SH "COPYRIGHTS AND LICENSES"
421 .IX Header "COPYRIGHTS AND LICENSES"
422 \&\s-1GVPE\s0 itself is distributed under the \s-1GENERAL PUBLIC LICENSE \s0(see the file
423 \&\s-1COPYING\s0 that should be part of your distribution).
424 .PP
425 In some configurations it uses modified versions of the tinc vpn suite,
426 which is also available under the \s-1GENERAL PUBLIC LICENSE.\s0