[ViewVC] Annotation of: cvs/gvpe/README


==== NAME ====

    GNU-VPE - Overview of the GNU Virtual Private Ethernet suite.


==== DESCRIPTION ====

    GVPE 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 GVPE.


==   WHAT IS A VPN?   ==

    VPN is an acronym, it stands for:

:       Virtual means that no physical network is created (of course), but a
        network is *emulated* by creating multiple tunnels between the
        member nodes by encapsulating and sending data over another
        transport network.

        Usually the emulated network is a normal IP or Ethernet, and the
        transport network is the Internet. However, using a VPN system like
        GVPE to connect nodes over other untrusted networks such as Wireless
        LAN is not uncommon.

:       Private means that non-participating nodes cannot decode ("sniff)"
        nor inject ("spoof") 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.

        In the case of GVPE, 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.

:       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 "vpn" solutions
        only create point-to-point tunnels, which in turn can be used to
        build larger networks.

        GVPE 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.


==   GVPE DESIGN GOALS   ==

:   SIMPLE DESIGN
        Cipher, HMAC 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. GVPE
        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.

:   EASY TO SETUP
        A few lines of config (the config file is shared unmodified between
        all hosts) and a single run of ``gvpectrl'' to generate the keys
        suffices to make it work.

:   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
        MAC address, e.g. to ensure that packets from a specific IP address
        come, in fact, from a specific host that is associated with that IP
        and not from another host.


==== PROGRAMS ====

    Vpe comes with two programs: one daemon (``gvpe'') and one control
    program (``gvpectrl'').

:   gvpectrl
        Is used to generate the keys, check and give an overview of of the
        configuration and contorl the daemon (restarting etc.).

:   gvpe
        Is the daemon used to establish and maintain connections to the
        other network members. It should be run on the gateway machine.


==== COMPILETIME CONFIGURATION ====

    Please have a look at the ``gvpe.osdep(5)'' manpage for
    platform-specific information.

    Here are a few recipes for compiling your gvpe, showing the extremes
    (fast, small, insecure OR slow, large, more secure), between you should
    choose:


==   AS LOW PACKET OVERHEAD AS POSSIBLE   ==

       ./configure --enable-hmac-length=4 --enable-rand-length=0

    Minimize the header overhead of VPN packets (the above will result in
    only 4 bytes of overhead over the raw ethernet frame). This is a
    insecure configuration because a HMAC length of 4 makes collision
    attacks based on the birthday paradox easy, though.


==   MINIMIZE CPU TIME REQUIRED   ==

       ./configure --enable-cipher=bf --enable-digest=md4

    Use the fastest cipher and digest algorithms currently available in
    gvpe. MD4 has been broken and is quite insecure, though.


==   MAXIMIZE SECURITY   ==

       ./configure --enable-hmac-length=16 --enable-rand-length=8 --enable-digest=sha1

    This uses a 16 byte HMAC 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
    SHA-224 and beyond, but support in openssl is missing as of writing this
    document.

    In general, remember that AES-128 seems to be more secure and faster
    than AES-192 or AES-256, more randomness helps against sniffing and a
    longer HMAC helps against spoofing. MD4 is a fast digest, SHA1 or
    RIPEMD160 are better, and Blowfish is a fast cipher (and also quite
    secure).


==== HOW TO SET UP A SIMPLE VPN ====

    In this section I will describe how to get a simple VPN consisting of
    three hosts up and running.


==   STEP 1: configuration   ==

    First you have to create a daemon configuation file and put it into the
    configuration directory. This is usually ``/etc/gvpe'', depending on how
    you configured gvpe, and can be overwritten using the ``-c'' commandline
    switch.

    Put the following lines into ``/etc/gvpe/gvpe.conf'':

       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

       node = first     # just a nickname
       hostname = first.example.net # the DNS name or IP address of the host

       node = second
       hostname = 133.55.82.9

       node = third
       hostname = third.example.net

    The only other file neccessary if the ``if-up'' script that initializes
    the local ethernet interface. Put the following lines into
    ``/etc/gvpe/if-up'' and make it execute (``chmod 755 /etc/gvpe/if-up''):

       #!/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

    This script will give each node a different IP address in the
    ``10.0/16'' network. The internal network (e.g. the ``eth0'' interface)
    should then be set to a subset of that network, e.g. ``10.0.1.0/24'' on
    node ``first'', ``10.0.2.0/24'' on node ``second'', and so on.

    By enabling routing on the gateway host that runs ``gvpe'' 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.


==   STEP 2: create the RSA key pairs for all hosts   ==

    Run the following command to generate all key pairs (that might take a
    while):

       gvpectrl -c /etc/gvpe -g

    This command will put the public keys into
    ``/etc/gvpe/pubkeys/*nodename*'' and the private keys into
    ``/etc/gvpe/hostkeys/*nodename*''.


==   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

    First all the config files without the hostkeys should be distributed:

       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

    Then the hostkeys should be copied:

       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

    You should now check the configration by issuing the command ``gvpectrl
    -c /etc/gvpe -s'' on each node and verify it's output.


==   STEP 4: starting gvpe   ==

    You should then start gvpe on each node by issuing a command like:

       gvpe -D -linfo first # first is the nodename

    This will make the gvpe stay in foreground. You should then see
    "connection established" messages. If you don't see them check your
    firewall and routing (use tcpdump ;).

    If this works you should check your networking setup by pinging various
    endpoints.

    To make gvpe run more permanently you can either run it as a daemon (by
    starting it without the ``-D'' switch), or, much better, from your
    inittab. I use a line like this on my systems:

       t1:2345:respawn:/opt/gvpe/sbin/gvpe -D -L first >/dev/null 2>&1


==   STEP 5: enjoy   ==

    ... and play around. Sending a -HUP (``gvpectrl -kHUP'') to the daemon
    will make it try to connect to all other nodes again. If you run it from
    inittab, as is recommended, ``gvpectrl -k'' (or simply ``killall gvpe'')
    will kill the daemon, start it again, making it read it's configuration
    files again.


==== SEE ALSO ====

    gvpe.osdep(5) for OS-depedendent information, gvpe.conf(5), gvpectrl(8),
    and for a description of the transports, protocol, and routing
    algorithm, gvpe.protocol(7).

    The GVPE mailinglist, at <http://lists.schmorp.de/>, or
    ``gvpe@lists.schmorp.de''.


==== AUTHOR ====

    Marc Lehmann <gvpe@schmorp.de>


==== COPYRIGHTS AND LICENSES ====

    GVPE itself is distributed under the GENERAL PUBLIC LICENSE (see the
    file COPYING that should be part of your distribution).

    In some configurations it uses modified versions of the tinc vpn suite,
    which is also available under the GENERAL PUBLIC LICENSE.

Revision:	1.8
Committed:	Fri Mar 18 01:53:05 2005 UTC (19 years, 1 month 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
Log Message:	* empty log message *
#	User	Rev	Content
1	pcg	1.1
2	pcg	1.2	==== NAME ====
3
4	pcg	1.6	GNU-VPE - Overview of the GNU Virtual Private Ethernet suite.
5	pcg	1.2
6
7			==== DESCRIPTION ====
8
9	pcg	1.7	GVPE is a suite designed to provide a virtual private network for
10	pcg	1.8	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	pcg	1.2
14	pcg	1.4
15	pcg	1.8	== WHAT IS A VPN? ==
16	pcg	1.4
17	pcg	1.8	VPN is an acronym, it stands for:
18	pcg	1.4
19	pcg	1.8	: 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	pcg	1.2
24	pcg	1.8	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	pcg	1.2
29	pcg	1.8	: 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	pcg	1.2
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	pcg	1.8	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	pcg	1.2
63			: EASY TO SETUP
64			A few lines of config (the config file is shared unmodified between
65	pcg	1.7	all hosts) and a single run of ``gvpectrl'' to generate the keys
66	pcg	1.2	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	pcg	1.7	traffic from this host. That makes it possible to filter packet by
71	pcg	1.2	MAC address, e.g. to ensure that packets from a specific IP address
72	pcg	1.7	come, in fact, from a specific host that is associated with that IP
73			and not from another host.
74	pcg	1.2
75
76			==== PROGRAMS ====
77
78	pcg	1.7	Vpe comes with two programs: one daemon (``gvpe'') and one control
79			program (``gvpectrl'').
80	pcg	1.2
81	pcg	1.7	: gvpectrl
82	pcg	1.3	Is used to generate the keys, check and give an overview of of the
83			configuration and contorl the daemon (restarting etc.).
84	pcg	1.2
85	pcg	1.7	: gvpe
86			Is the daemon used to establish and maintain connections to the
87	pcg	1.2	other network members. It should be run on the gateway machine.
88
89
90	pcg	1.3	==== COMPILETIME CONFIGURATION ====
91	pcg	1.2
92	pcg	1.7	Please have a look at the ``gvpe.osdep(5)'' manpage for
93			platform-specific information.
94	pcg	1.6
95	pcg	1.8	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	pcg	1.2
99
100			== AS LOW PACKET OVERHEAD AS POSSIBLE ==
101
102	pcg	1.3	./configure --enable-hmac-length=4 --enable-rand-length=0
103	pcg	1.2
104	pcg	1.3	Minimize the header overhead of VPN packets (the above will result in
105	pcg	1.8	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	pcg	1.2
109
110			== MINIMIZE CPU TIME REQUIRED ==
111
112	pcg	1.3	./configure --enable-cipher=bf --enable-digest=md4
113	pcg	1.2
114	pcg	1.7	Use the fastest cipher and digest algorithms currently available in
115	pcg	1.8	gvpe. MD4 has been broken and is quite insecure, though.
116	pcg	1.2
117
118			== MAXIMIZE SECURITY ==
119
120	pcg	1.3	./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	pcg	1.8	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	pcg	1.2
128			In general, remember that AES-128 seems to be more secure and faster
129	pcg	1.3	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	pcg	1.2
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	pcg	1.7	configuration directory. This is usually ``/etc/gvpe'', depending on how
145			you configured gvpe, and can be overwritten using the ``-c'' commandline
146	pcg	1.2	switch.
147
148	pcg	1.7	Put the following lines into ``/etc/gvpe/gvpe.conf'':
149	pcg	1.2
150	pcg	1.3	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	pcg	1.2
154	pcg	1.3	node = first # just a nickname
155			hostname = first.example.net # the DNS name or IP address of the host
156	pcg	1.2
157	pcg	1.3	node = second
158			hostname = 133.55.82.9
159	pcg	1.2
160	pcg	1.3	node = third
161			hostname = third.example.net
162	pcg	1.2
163			The only other file neccessary if the ``if-up'' script that initializes
164			the local ethernet interface. Put the following lines into
165	pcg	1.7	``/etc/gvpe/if-up'' and make it execute (``chmod 755 /etc/gvpe/if-up''):
166	pcg	1.2
167	pcg	1.3	#!/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	pcg	1.2
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	pcg	1.7	By enabling routing on the gateway host that runs ``gvpe'' all nodes
180	pcg	1.2	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	pcg	1.7	gvpectrl -c /etc/gvpe -g
191	pcg	1.2
192			This command will put the public keys into
193	pcg	1.7	``/etc/gvpe/pubkeys/nodename'' and the private keys into
194			``/etc/gvpe/hostkeys/nodename''.
195	pcg	1.2
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	pcg	1.7	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	pcg	1.2
209			Then the hostkeys should be copied:
210
211	pcg	1.7	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	pcg	1.2
215	pcg	1.7	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	pcg	1.2
218
219	pcg	1.7	== STEP 4: starting gvpe ==
220	pcg	1.2
221	pcg	1.7	You should then start gvpe on each node by issuing a command like:
222	pcg	1.2
223	pcg	1.7	gvpe -D -linfo first # first is the nodename
224	pcg	1.2
225	pcg	1.7	This will make the gvpe stay in foreground. You should then see
226	pcg	1.2	"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	pcg	1.7	To make gvpe run more permanently you can either run it as a daemon (by
233	pcg	1.2	starting it without the ``-D'' switch), or, much better, from your
234			inittab. I use a line like this on my systems:
235
236	pcg	1.7	t1:2345:respawn:/opt/gvpe/sbin/gvpe -D -L first >/dev/null 2>&1
237	pcg	1.2
238
239			== STEP 5: enjoy ==
240
241	pcg	1.7	... and play around. Sending a -HUP (``gvpectrl -kHUP'') to the daemon
242	pcg	1.2	will make it try to connect to all other nodes again. If you run it from
243	pcg	1.7	inittab, as is recommended, ``gvpectrl -k'' (or simply ``killall gvpe'')
244	pcg	1.2	will kill the daemon, start it again, making it read it's configuration
245			files again.
246
247
248			==== SEE ALSO ====
249
250	pcg	1.7	gvpe.osdep(5) for OS-depedendent information, gvpe.conf(5), gvpectrl(8),
251	pcg	1.8	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	pcg	1.2
257
258			==== AUTHOR ====
259
260	pcg	1.8	Marc Lehmann <gvpe@schmorp.de>
261	pcg	1.6
262
263			==== COPYRIGHTS AND LICENSES ====
264
265	pcg	1.8	GVPE itself is distributed under the GENERAL PUBLIC LICENSE (see the
266			file COPYING that should be part of your distribution).
267	pcg	1.6
268			In some configurations it uses modified versions of the tinc vpn suite,
269			which is also available under the GENERAL PUBLIC LICENSE.
270