x SuSE Linux 13.1-RELEASE x
x SuSE Linux 13.1-RELEASEx
OPENVPN EXAMPLES(5) Configuration files OPENVPN EXAMPLES(5)
NAME
openvpn examples - Secure IP tunnel daemon
INTRODUCTION
This man page gives a few simple examples to create OpenVPN setups and
configuration files.
SMALL OPENVPN SETUP WITH PEER-FINGERPRINT
This section consists of instructions how to build a small OpenVPN set-
up with the peer-fingerprint option. This has the advantage of being
easy to setup and should be suitable for most small lab and home setups
without the need for a PKI. For bigger scale setup setting up a PKI
(e.g. via easy-rsa) is still recommended.
Both server and client configuration can be further modified to cus-
tomise the setup.
Server setup
1. Install openvpn
Compile from source-code (see INSTALL file) or install via a distri-
bution (apt/yum/ports) or via installer (Windows).
2. Generate a self-signed certificate for the server:
openssl req -x509 -newkey ec:<(openssl ecparam -name secp384r1) -keyout server.key -out server.crt -nodes -sha256 -days 3650 -subj '/CN=server'
3. Generate SHA256 fingerprint of the server certificate
Use the OpenSSL command line utility to view the fingerprint of just
created certificate:
openssl x509 -fingerprint -sha256 -in server.crt -noout
This output something similar to:
SHA256 Fingerprint=00:11:22:33:44:55:66:77:88:99:aa:bb:cc:dd:ee:ff:00:11:22:33:44:55:66:77:88:99:aa:bb:cc:dd:ee:ff
4. Write a server configuration (server.conf):
# The server certificate we created in step 1
cert server.crt
key server.key
dh none
dev tun
# Listen on IPv6+IPv4 simultaneously
proto udp6
# The ip address the server will distribute
server 10.8.0.0 255.255.255.0
server-ipv6 fd00:6f76:706e::/64
# A tun-mtu of 1400 avoids problems of too big packets after VPN encapsulation
tun-mtu 1400
# The fingerprints of your clients. After adding/removing one here restart the
# server
<peer-fingerprint>
</peer-fingerprint>
# Notify clients when you restart the server to reconnect quickly
explicit-exit-notify 1
# Ping every 60s, restart if no data received for 5 minutes
keepalive 60 300
5. Add at least one client as described in the client section.
6.
Start the server.
o On systemd based distributions move server.crt, server.key
and server.conf to /etc/openvpn/server and start it via
systemctl
sudo mv server.conf server.key server.crt /etc/openvpn/server
sudo systemctl start openvpn-server@server
Adding a client
1. Install OpenVPN
2. Generate a self-signed certificate for the client. In this example
the client name is alice. Each client should have a unique name.
Replace alice with a different name for each client.
openssl req -x509 -newkey ec:<(openssl ecparam -name secp384r1) -nodes -sha256 -days 3650 -subj '/CN=alice'
This generate a certificate and a key for the client. The output of
the command will look something like this:
-----BEGIN PRIVATE KEY-----
[base64 content]
-----END PRIVATE KEY-----
-----
-----BEGIN CERTIFICATE-----
[base 64 content]
-----END CERTIFICATE-----
3. Create a new client configuration file. In this example we will name
the file alice.ovpn:
# The name of your server to connect to
remote yourserver.example.net
client
# use a random source port instead the fixed 1194
nobind
# Uncomment the following line if you want to route
# all traffic via the VPN
# redirect-gateway def1 ipv6
# To set a DNS server
# dhcp-option DNS 192.168.234.1
<key>
-----BEGIN PRIVATE KEY-----
[Insert here the key created in step 2]
-----END PRIVATE KEY-----
</key>
<cert>
-----BEGIN CERTIFICATE-----
[Insert here the certificate created in step 2]
-----END CERTIFICATE-----
</cert>
# This is the fingerprint of the server that we trust. We generated this fingerprint
# in step 2 of the server setup
peer-fingerprint 00:11:22:33:44:55:66:77:88:99:aa:bb:cc:dd:ee:ff:00:11:22:33:44:55:66:77:88:99:aa:bb:cc:dd:ee:ff
# The tun-mtu of the client should match the server MTU
tun-mtu 1400
dev tun
4. Generate the fingerprint of the client certificate. For that we will
let OpenSSL read the client configuration file as the x509 command
will ignore anything that is not between the begin and end markers
of the certificate:
openssl x509 -fingerprint -sha256 -noout -in alice.ovpn
This will again output something like
SHA256 Fingerprint=ff:ee:dd:cc:bb:aa:99:88:77:66:55:44:33:22:11:00:ff:ee:dd:cc:bb:aa:99:88:77:66:55:44:33:22:11:00
5. Edit the server.conf configuration file and add this new client fin-
gerprint as additional line between <peer-fingerprint> and
</peer-fingerprint>
After adding two clients the part of configuration would look like
this:
<peer-fingerprint>
ff:ee:dd:cc:bb:aa:99:88:77:66:55:44:33:22:11:00:ff:ee:dd:cc:bb:aa:99:88:77:66:55:44:33:22:11:00
99:88:77:66:55:44:33:22:11:00:ff:ee:dd:cc:bb:aa:99:88:77:66:55:44:33:22:11:00:88:77:66:55:44:33
</peer-fingperint>
6. (optional) if the client is an older client that does not support
the peer-fingerprint (e.g. OpenVPN 2.5 and older, OpenVPN Connect
3.3 and older), the client config alice.ovpn can be modified to
still work with these clients.
Remove the line starting with peer-fingerprint. Then add a new <ca>
section at the end of the configuration file with the contents of
the server.crt created in step 2 of the server setup. The end of
alice.ovpn file should like:
[...] # Beginning of the file skipped
</cert>
# The tun-mtu of the client should match the server MTU
tun-mtu 1400
dev tun
<ca>
[contents of the server.crt]
</ca>
Note that we put the <ca> section after the <cert> section to make
the fingerprint generation from step 4 still work since it will only
use the first certificate it finds.
7. Import the file into the OpenVPN client or just use the openvpn
alice.ovpn to start the VPN.
EXAMPLES
Prior to running these examples, you should have OpenVPN installed on
two machines with network connectivity between them. If you have not
yet installed OpenVPN, consult the INSTALL file included in the OpenVPN
distribution.
Firewall Setup:
If firewalls exist between the two machines, they should be set to for-
ward the port OpenVPN is configured to use, in both directions. The
default for OpenVPN is 1194/udp. If you do not have control over the
firewalls between the two machines, you may still be able to use Open-
VPN by adding --ping 15 to each of the openvpn commands used below in
the examples (this will cause each peer to send out a UDP ping to its
remote peer once every 15 seconds which will cause many stateful fire-
walls to forward packets in both directions without an explicit fire-
wall rule).
Please see your operating system guides for how to configure the fire-
wall on your systems.
VPN Address Setup:
For purposes of our example, our two machines will be called bob.exam-
ple.com and alice.example.com. If you are constructing a VPN over the
internet, then replace bob.example.com and alice.example.com with the
internet hostname or IP address that each machine will use to contact
the other over the internet.
Now we will choose the tunnel endpoints. Tunnel endpoints are private
IP addresses that only have meaning in the context of the VPN. Each
machine will use the tunnel endpoint of the other machine to access it
over the VPN. In our example, the tunnel endpoint for bob.example.com
will be 10.4.0.1 and for alice.example.com, 10.4.0.2.
Once the VPN is established, you have essentially created a secure
alternate path between the two hosts which is addressed by using the
tunnel endpoints. You can control which network traffic passes between
the hosts (a) over the VPN or (b) independently of the VPN, by choosing
whether to use (a) the VPN endpoint address or (b) the public internet
address, to access the remote host. For example if you are on bob.exam-
ple.com and you wish to connect to alice.example.com via ssh without
using the VPN (since ssh has its own built-in security) you would use
the command ssh alice.example.com. However in the same scenario, you
could also use the command telnet 10.4.0.2 to create a telnet session
with alice.example.com over the VPN, that would use the VPN to secure
the session rather than ssh.
You can use any address you wish for the tunnel endpoints but make sure
that they are private addresses (such as those that begin with 10 or
192.168) and that they are not part of any existing subnet on the net-
works of either peer, unless you are bridging. If you use an address
that is part of your local subnet for either of the tunnel endpoints,
you will get a weird feedback loop.
Example 1: A simple tunnel without security (not recommended)
On bob:
openvpn --remote alice.example.com --dev tun1 \
--ifconfig 10.4.0.1 10.4.0.2 --verb 9
On alice:
openvpn --remote bob.example.com --dev tun1 \
--ifconfig 10.4.0.2 10.4.0.1 --verb 9
Now verify the tunnel is working by pinging across the tunnel.
On bob:
ping 10.4.0.2
On alice:
ping 10.4.0.1
The --verb 9 option will produce verbose output, similar to the tcp-
dump(8) program. Omit the --verb 9 option to have OpenVPN run quietly.
Example 2: A tunnel with self-signed certificates and fingerprint
First build a self-signed certificate on bob and display its finger-
print.
openssl req -x509 -newkey ec:<(openssl ecparam -name secp384r1) -keyout bob.pem -out bob.pem -nodes -sha256 -days 3650 -subj '/CN=bob'
openssl x509 -noout -sha256 -fingerprint -in bob.pem
and the same on alice:
openssl req -x509 -newkey ec:<(openssl ecparam -name secp384r1) -keyout alice.pem -out alice.pem -nodes -sha256 -days 3650 -subj '/CN=alice'
openssl x509 -noout -sha256 -fingerprint -in alice.pem
These commands will build a text file called bob.pem or alice.pem (in
ascii format) that contain both self-signed certificate and key and
show the fingerprint of the certificates. Transfer the fingerprints
over a secure medium such as by using the scp(1) or ssh(1) program.
On bob:
openvpn --ifconfig 10.4.0.1 10.4.0.2 --tls-server --dev tun --dh none \
--cert bob.pem --key bob.pem --cipher AES-256-GCM \
--peer-fingerprint "$fingerprint_of_alices_cert"
On alice:
openvpn --remote bob.example.com --tls-client --dev tun1 \
--ifconfig 10.4.0.2 10.4.0.1 --cipher AES-256-GCM \
--cert alice.pem --key alice.pem \
--peer-fingerprint "$fingerprint_of_bobs_cert"
Now verify the tunnel is working by pinging across the tunnel.
On bob:
ping 10.4.0.2
On alice:
ping 10.4.0.1
Note: This example use a elliptic curve (secp384), which allows --dh to
be set to none.
Example 3: A tunnel with full PKI and TLS-based security
For this test, we will designate bob as the TLS client and alice as the
TLS server.
Note: The client or server designation only has meaning for the TLS
subsystem. It has no bearing on OpenVPN's peer-to-peer,
UDP-based communication model.*
First, build a separate certificate/key pair for both bob and alice
(see above where --cert is discussed for more info). Then construct
Diffie Hellman parameters (see above where --dh is discussed for more
info). You can also use the included test files client.crt, client.key,
server.crt, server.key and ca.crt. The .crt files are certificates/pub-
lic-keys, the .key files are private keys, and ca.crt is a certifica-
tion authority who has signed both client.crt and server.crt. For
Diffie Hellman parameters you can use the included file dh2048.pem.
WARNING:
All client, server, and certificate authority certificates and
keys included in the OpenVPN distribution are totally insecure
and should be used for testing only.
On bob:
openvpn --remote alice.example.com --dev tun1 \
--ifconfig 10.4.0.1 10.4.0.2 \
--tls-client --ca ca.crt \
--cert client.crt --key client.key \
--reneg-sec 60 --verb 5
On alice:
openvpn --remote bob.example.com --dev tun1 \
--ifconfig 10.4.0.2 10.4.0.1 \
--tls-server --dh dh1024.pem --ca ca.crt \
--cert server.crt --key server.key \
--reneg-sec 60 --verb 5
Now verify the tunnel is working by pinging across the tunnel.
On bob:
ping 10.4.0.2
On alice:
ping 10.4.0.1
Notice the --reneg-sec 60 option we used above. That tells OpenVPN to
renegotiate the data channel keys every minute. Since we used --verb 5
above, you will see status information on each new key negotiation.
For production operations, a key renegotiation interval of 60 seconds
is probably too frequent. Omit the --reneg-sec 60 option to use Open-
VPN's default key renegotiation interval of one hour.
Routing:
Assuming you can ping across the tunnel, the next step is to route a
real subnet over the secure tunnel. Suppose that bob and alice have two
network interfaces each, one connected to the internet, and the other
to a private network. Our goal is to securely connect both private net-
works. We will assume that bob's private subnet is 10.0.0.0/24 and
alice's is 10.0.1.0/24.
First, ensure that IP forwarding is enabled on both peers. On Linux,
enable routing:
echo 1 > /proc/sys/net/ipv4/ip_forward
This setting is not persistent. Please see your operating systems doc-
umentation how to properly configure IP forwarding, which is also per-
sistent through system boots.
If your system is configured with a firewall. Please see your operat-
ing systems guide on how to configure the firewall. You typically want
to allow traffic coming from and going to the tun/tap adapter OpenVPN
is configured to use.
On bob:
route add -net 10.0.1.0 netmask 255.255.255.0 gw 10.4.0.2
On alice:
route add -net 10.0.0.0 netmask 255.255.255.0 gw 10.4.0.1
Now any machine on the 10.0.0.0/24 subnet can access any machine on the
10.0.1.0/24 subnet over the secure tunnel (or vice versa).
In a production environment, you could put the route command(s) in a
script and execute with the --up option.
OPENVPN EXAMPLES(5)
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