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.
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 ma-
chine 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 al-
ternate path between the two hosts which is addressed by using the tun-
nel 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
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 static-key security (i.e. using a pre-shared se-
cret)
First build a static key on bob.
openvpn --genkey --secret key
This command will build a key file called key (in ascii format). Now
copy key to alice.example.com over a secure medium such as by using the
scp(1) program.
On bob:
openvpn --remote alice.example.com --dev tun1 \
--ifconfig 10.4.0.1 10.4.0.2 --verb 5 \
--secret key
On alice:
openvpn --remote bob.example.com --dev tun1 \
--ifconfig 10.4.0.2 10.4.0.1 --verb 5 \
--secret key
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
Example 3: A tunnel with full 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 al-
ice'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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