Difference between revisions of "OpenVPN"
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{{Accuracy|Investigate if a routing protocol like RIP, QUAGGA, BIRD, etc can be used}} | {{Accuracy|Investigate if a routing protocol like RIP, QUAGGA, BIRD, etc can be used}} | ||
| − | By default, all IP packets on a LAN addressed to a different subnet get sent to the default gateway. If the LAN/VPN gateway is also the default gateway, there is no problem and the packets get properly forwarded | + | By default, all IP packets on a LAN addressed to a different subnet get sent to the default gateway. If the LAN/VPN gateway is also the default gateway, there is no problem and the packets get properly forwarded. If not, the gateway has no way of knowing where to send the packets. There are a couple of solutions to this problem. |
| − | * Add a static route to the default gateway routing the VPN subnet to the LAN/VPN gateway. | + | * Add a static route to the default gateway routing the VPN subnet to the LAN/VPN gateway's IP address. |
* Add a static route on each host on the LAN that needs to send IP packets back to the VPN. | * Add a static route on each host on the LAN that needs to send IP packets back to the VPN. | ||
| − | * Use iptables' NAT feature on the LAN/VPN gateway to masquerade the IP packets. | + | * Use [[iptables]]' NAT feature on the LAN/VPN gateway to masquerade the incoming VPN IP packets. |
===Route a server side LAN to a client=== | ===Route a server side LAN to a client=== | ||
Revision as of 08:06, 27 August 2012
This article describes a basic installation and configuration of OpenVPN, suitable for private and small business use. For more detailed information, please see the official OpenVPN 2.2 man page and the OpenVPN documentation.
OpenVPN is a robust and highly flexible VPN daemon. OpenVPN supports SSL/TLS security, ethernet bridging, TCP or UDP tunnel transport through proxies or NAT, support for dynamic IP addresses and DHCP, scalability to hundreds or thousands of users, and portability to most major OS platforms.
OpenVPN is tightly bound to the OpenSSL library, and derives much of its crypto capabilities from it.
OpenVPN supports conventional encryption using a pre-shared secret key (Static Key mode) or public key security (SSL/TLS mode) using client & server certificates. OpenVPN also supports non-encrypted TCP/UDP tunnels.
OpenVPN is designed to work with the TUN/TAP virtual networking interface that exists on most platforms.
Overall, OpenVPN aims to offer many of the key features of IPSec but with a relatively lightweight footprint.
OpenVPN was written by James Yonan and is published under the GNU General Public License (GPL).
Contents
- 1 Install OpenVPN
- 2 Configure the system for TUN/TAP support
- 3 Connect to a VPN provided by a third party
- 4 Create a Public Key Infrastructure (PKI) from scratch
- 5 A basic L3 IP routing configuration
- 6 Starting OpenVPN
- 7 Advanced L3 IP routing
- 8 L2 Ethernet bridging
- 9 Contributions that do not yet fit into the main article
Install OpenVPN
Install openvpn from the official repositories.
Configure the system for TUN/TAP support
OpenVPN requires TUN/TAP support. Make sure to load the TUN module.
/etc/modules-load.d/tun.conf
# Load tun.ko at boot tun
Connect to a VPN provided by a third party
To connect to a VPN provided by a third party, most of the following can most likely be ignored. Use the certificates and instructions given by your provider, for instance see: Airvpn.
Create a Public Key Infrastructure (PKI) from scratch
If you are setting up OpenVPN from scratch, you will need to create a Public Key Infrastructure (PKI).
Create the needed certificates and keys by following: Create a Public Key Infrastructure Using the easy-rsa Scripts.
The final step of the key creation process is to copy the files needed to the correct machines through a secure channel.
The public ca.crt certificate is needed on all servers and clients. The private ca.key key is secret and only needed on the key generating machine.
A server needs server.crt, and dh2048.pem (public), and server.key and ta.key (private).
A client needs client.crt (public), and client.key and ta.key (private).
A basic L3 IP routing configuration
OpenVPN is an extremely versatile piece of software and many configurations are possible, in fact machines can be both "servers" and "clients", blurring the distinction between server and client.
What really distinguishes a server from a client (apart from the type of certificate used) is the configuration file itself. The openvpn daemon startup script reads all the .conf configuration files it finds in /etc/openvpn on startup and acts accordingly. In fact if it finds more than one configuration file, it will start one OpenVPN processes per configuration file.
This article explains how to setup a server called elmer, and a client that connects to it called bugs. More servers and clients can easily be added, by creating more key/certificate pairs and adding more server and client configuration files.
The OpenVPN package comes with a collection of example configuration files for different purposes. The sample server and client configuration files make an ideal starting point for a basic OpenVPN setup with the following features:
- Uses Public Key Infrastructure (PKI) for authentication.
- Creates a VPN using a virtual TUN network interface (OSI L3 IP routing).
- Listens for client connections on UDP port 1194 (OpenVPN's official IANA port number).
- Distributes virtual addresses to connecting clients from the 10.8.0.0/24 subnet.
For more advanced configurations, please see the official OpenVPN 2.2 man page and the OpenVPN documentation.
The server configuration file
Copy the example server configuration file to /etc/openvpn/server.conf
# cp /usr/share/openvpn/examples/server.conf /etc/openvpn/server.conf
Edit the following:
- The ca, cert, key, and dh parameters to reflect the path and names of the keys and certificates. Specifying the paths will allow you to run the OpenVPN executable from any directory for testing purposes.
- Enable the SSL/TLS HMAC handshake protection. Note the use of the parameter 0 for a server.
- It is recommended to run OpenVPN with reduced privileges once it has initialized, do this by uncommenting the user and group directives.
/etc/openvpn/server.conf
ca /etc/openvpn/ca.crt cert /etc/openvpn/elmer.crt key /etc/openvpn/elmer.key dh /etc/openvpn/dh2048.pem . . tls-auth /etc/openvpn/ta.key 0 . . user nobody group nobody
The client configuration file
Copy the example client configuration file to /etc/openvpn/client.conf
# cp /usr/share/openvpn/examples/client.conf /etc/openvpn/client.conf
Edit the following:
- The remote directive to reflect the server's Fully Qualified Domain Name, hostname (as known to the client) or IP address.
- Uncomment the user and group directives to drop privileges.
- The ca, cert, and key parameters to reflect the path and names of the keys and certificates.
- Enable the SSL/TLS HMAC handshake protection. Note the use of the parameter 1 for a client.
/etc/openvpn/client.conf
remote elmer.acmecorp.org 1194 . . user nobody group nobody . . ca /etc/openvpn/ca.crt cert /etc/openvpn/bugs.crt key /etc/openvpn/bugs.key . . tls-auth /etc/openvpn/ta.key 1
Testing the OpenVPN configuration
Run # openvpn /etc/openvpn/server.conf on the server, and # openvpn /etc/openvpn/client.conf on the client. You should see something similar to this:
# openvpn /etc/openvpn/server.conf
Wed Dec 28 14:41:26 2011 OpenVPN 2.2.1 x86_64-unknown-linux-gnu [SSL] [LZO2] [EPOLL] [eurephia] built on Aug 13 2011 Wed Dec 28 14:41:26 2011 NOTE: OpenVPN 2.1 requires '--script-security 2' or higher to call user-defined scripts or executables Wed Dec 28 14:41:26 2011 Diffie-Hellman initialized with 2048 bit key Wed Dec 28 14:41:26 2011 TLS-Auth MTU parms [ L:1542 D:138 EF:38 EB:0 ET:0 EL:0 ] Wed Dec 28 14:41:26 2011 Socket Buffers: R=[126976->131072] S=[126976->131072] Wed Dec 28 14:41:26 2011 ROUTE default_gateway=10.66.0.1 Wed Dec 28 14:41:26 2011 TUN/TAP device tun0 opened Wed Dec 28 14:41:26 2011 TUN/TAP TX queue length set to 100 Wed Dec 28 14:41:26 2011 /usr/sbin/ip link set dev tun0 up mtu 1500 Wed Dec 28 14:41:26 2011 /usr/sbin/ip addr add dev tun0 local 10.8.0.1 peer 10.8.0.2 Wed Dec 28 14:41:26 2011 /usr/sbin/ip route add 10.8.0.0/24 via 10.8.0.2 Wed Dec 28 14:41:26 2011 Data Channel MTU parms [ L:1542 D:1450 EF:42 EB:135 ET:0 EL:0 AF:3/1 ] Wed Dec 28 14:41:26 2011 GID set to nobody Wed Dec 28 14:41:26 2011 UID set to nobody Wed Dec 28 14:41:26 2011 UDPv4 link local (bound): [undef]:1194 Wed Dec 28 14:41:26 2011 UDPv4 link remote: [undef] Wed Dec 28 14:41:26 2011 MULTI: multi_init called, r=256 v=256 Wed Dec 28 14:41:26 2011 IFCONFIG POOL: base=10.8.0.4 size=62 Wed Dec 28 14:41:26 2011 IFCONFIG POOL LIST Wed Dec 28 14:41:26 2011 Initialization Sequence Completed Wed Dec 28 14:41:51 2011 MULTI: multi_create_instance called Wed Dec 28 14:41:51 2011 95.126.136.73:48904 Re-using SSL/TLS context Wed Dec 28 14:41:51 2011 95.126.136.73:48904 LZO compression initialized Wed Dec 28 14:41:51 2011 95.126.136.73:48904 Control Channel MTU parms [ L:1542 D:138 EF:38 EB:0 ET:0 EL:0 ] Wed Dec 28 14:41:51 2011 95.126.136.73:48904 Data Channel MTU parms [ L:1542 D:1450 EF:42 EB:135 ET:0 EL:0 AF:3/1 ] Wed Dec 28 14:41:51 2011 95.126.136.73:48904 Local Options hash (VER=V4): '530fdded' Wed Dec 28 14:41:51 2011 95.126.136.73:48904 Expected Remote Options hash (VER=V4): '41690919' Wed Dec 28 14:41:51 2011 95.126.136.73:48904 TLS: Initial packet from 95.126.136.73:48904, sid=163f4a5e e0399137 Wed Dec 28 14:41:53 2011 95.126.136.73:48904 VERIFY OK: depth=1, /C=US/ST=CA/L=Acme Acres/O=Acme/CN=Acme-CA/name=Acme-CA/emailAddress=roadrunner@acmecorp.org Wed Dec 28 14:41:53 2011 95.126.136.73:48904 VERIFY OK: depth=0, /C=US/ST=CA/L=Acme Acres/O=Acme/CN=bugs/name=Acme-CA/emailAddress=roadrunner@acmecorp.org Wed Dec 28 14:41:54 2011 95.126.136.73:48904 Data Channel Encrypt: Cipher 'BF-CBC' initialized with 128 bit key Wed Dec 28 14:41:54 2011 95.126.136.73:48904 Data Channel Encrypt: Using 160 bit message hash 'SHA1' for HMAC authentication Wed Dec 28 14:41:54 2011 95.126.136.73:48904 Data Channel Decrypt: Cipher 'BF-CBC' initialized with 128 bit key Wed Dec 28 14:41:54 2011 95.126.136.73:48904 Data Channel Decrypt: Using 160 bit message hash 'SHA1' for HMAC authentication Wed Dec 28 14:41:54 2011 95.126.136.73:48904 Control Channel: TLSv1, cipher TLSv1/SSLv3 DHE-RSA-AES256-SHA, 2048 bit RSA Wed Dec 28 14:41:54 2011 95.126.136.73:48904 [bugs] Peer Connection Initiated with 95.126.136.73:48904 Wed Dec 28 14:41:54 2011 bugs/95.126.136.73:48904 MULTI: Learn: 10.8.0.6 -> bugs/95.126.136.73:48904 Wed Dec 28 14:41:54 2011 bugs/95.126.136.73:48904 MULTI: primary virtual IP for bugs/95.126.136.73:48904: 10.8.0.6 Wed Dec 28 14:41:57 2011 bugs/95.126.136.73:48904 PUSH: Received control message: 'PUSH_REQUEST' Wed Dec 28 14:41:57 2011 bugs/95.126.136.73:48904 SENT CONTROL [bugs]: 'PUSH_REPLY,route 10.8.0.1,topology net30,ping 10,ping-restart 120,ifconfig 10.8.0.6 10.8.0.5' (status=1)
# openvpn /etc/openvpn/client.conf
Wed Dec 28 14:41:50 2011 OpenVPN 2.2.1 i686-pc-linux-gnu [SSL] [LZO2] [EPOLL] [eurephia] built on Aug 13 2011 Wed Dec 28 14:41:50 2011 NOTE: OpenVPN 2.1 requires '--script-security 2' or higher to call user-defined scripts or executables Wed Dec 28 14:41:50 2011 LZO compression initialized Wed Dec 28 14:41:50 2011 Control Channel MTU parms [ L:1542 D:138 EF:38 EB:0 ET:0 EL:0 ] Wed Dec 28 14:41:50 2011 Socket Buffers: R=[114688->131072] S=[114688->131072] Wed Dec 28 14:41:51 2011 Data Channel MTU parms [ L:1542 D:1450 EF:42 EB:135 ET:0 EL:0 AF:3/1 ] Wed Dec 28 14:41:51 2011 Local Options hash (VER=V4): '41690919' Wed Dec 28 14:41:51 2011 Expected Remote Options hash (VER=V4): '530fdded' Wed Dec 28 14:41:51 2011 NOTE: UID/GID downgrade will be delayed because of --client, --pull, or --up-delay Wed Dec 28 14:41:51 2011 UDPv4 link local: [undef] Wed Dec 28 14:41:51 2011 UDPv4 link remote: 85.93.204.250:1194 Wed Dec 28 14:41:51 2011 TLS: Initial packet from 85.93.204.250:1194, sid=5f379f35 50c9ab11 Wed Dec 28 14:41:52 2011 VERIFY OK: depth=1, /C=US/ST=CA/L=Acme Acres/O=Acme/CN=Acme-CA/name=Acme-CA/emailAddress=roadrunner@acmecorp.org Wed Dec 28 14:41:52 2011 VERIFY OK: nsCertType=SERVER Wed Dec 28 14:41:52 2011 VERIFY OK: depth=0, /C=US/ST=CA/L=Acme Acres/O=Acme/CN=elmer/name=Acme-CA/emailAddress=roadrunner@acmecorp.org Wed Dec 28 14:41:54 2011 Data Channel Encrypt: Cipher 'BF-CBC' initialized with 128 bit key Wed Dec 28 14:41:54 2011 Data Channel Encrypt: Using 160 bit message hash 'SHA1' for HMAC authentication Wed Dec 28 14:41:54 2011 Data Channel Decrypt: Cipher 'BF-CBC' initialized with 128 bit key Wed Dec 28 14:41:54 2011 Data Channel Decrypt: Using 160 bit message hash 'SHA1' for HMAC authentication Wed Dec 28 14:41:54 2011 Control Channel: TLSv1, cipher TLSv1/SSLv3 DHE-RSA-AES256-SHA, 2048 bit RSA Wed Dec 28 14:41:54 2011 [elmer] Peer Connection Initiated with 85.93.204.250:1194 Wed Dec 28 14:41:57 2011 SENT CONTROL [elmer]: 'PUSH_REQUEST' (status=1) Wed Dec 28 14:41:57 2011 PUSH: Received control message: 'PUSH_REPLY,route 10.8.0.1,topology net30,ping 10,ping-restart 120,ifconfig 10.8.0.6 10.8.0.5' Wed Dec 28 14:41:57 2011 OPTIONS IMPORT: timers and/or timeouts modified Wed Dec 28 14:41:57 2011 OPTIONS IMPORT: --ifconfig/up options modified Wed Dec 28 14:41:57 2011 OPTIONS IMPORT: route options modified Wed Dec 28 14:41:57 2011 ROUTE default_gateway=10.64.64.64 Wed Dec 28 14:41:57 2011 TUN/TAP device tun1 opened Wed Dec 28 14:41:57 2011 TUN/TAP TX queue length set to 100 Wed Dec 28 14:41:57 2011 /usr/sbin/ip link set dev tun1 up mtu 1500 Wed Dec 28 14:41:57 2011 /usr/sbin/ip addr add dev tun1 local 10.8.0.6 peer 10.8.0.5 Wed Dec 28 14:41:57 2011 /usr/sbin/ip route add 10.8.0.1/32 via 10.8.0.5 Wed Dec 28 14:41:57 2011 GID set to nobody Wed Dec 28 14:41:57 2011 UID set to nobody Wed Dec 28 14:41:57 2011 Initialization Sequence Completed
On the server, find the IP assigned to the tunX device:
# ip addr show
.
.
.
40: tun0: <POINTOPOINT,MULTICAST,NOARP,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UNKNOWN qlen 100
link/none
inet 10.8.0.1 peer 10.8.0.2/32 scope global tun0
Here we see that the server end of the tunnel has been given the IP address 10.8.0.1.
Do the same on the client:
# ip addr show
.
.
.
37: tun1: <POINTOPOINT,MULTICAST,NOARP,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UNKNOWN qlen 100
link/none
inet 10.8.0.6 peer 10.8.0.5/32 scope global tun1
And the client side has been given the IP 10.8.0.6.
Now try pinging the interfaces.
On the server:
# ping 10.8.0.6
PING 10.8.0.6 (10.8.0.6) 56(84) bytes of data. 64 bytes from 10.8.0.6: icmp_req=1 ttl=64 time=238 ms 64 bytes from 10.8.0.6: icmp_req=2 ttl=64 time=237 ms 64 bytes from 10.8.0.6: icmp_req=3 ttl=64 time=205 ms ^C --- 10.8.0.6 ping statistics --- 3 packets transmitted, 3 received, 0% packet loss, time 2002ms rtt min/avg/max/mdev = 205.862/227.266/238.788/15.160 ms
On the client:
# ping 10.8.0.1
PING 10.8.0.1 (10.8.0.1) 56(84) bytes of data. 64 bytes from 10.8.0.1: icmp_req=1 ttl=64 time=158 ms 64 bytes from 10.8.0.1: icmp_req=2 ttl=64 time=158 ms 64 bytes from 10.8.0.1: icmp_req=3 ttl=64 time=157 ms ^C --- 10.8.0.1 ping statistics --- 3 packets transmitted, 3 received, 0% packet loss, time 2001ms rtt min/avg/max/mdev = 157.426/158.278/158.940/0.711 ms
You now have a working OpenVPN installation, and your client (bugs) will be able to use services on the server (elmer), and vice versa.
Starting OpenVPN
To manually start OpenVPN (both server and client), run:
# rc.d start openvpn
To have your system run OpenVPN automatically at system start, add openvpn to the daemon array in /etc/rc.conf.
Advanced L3 IP routing
Prerequisites for routing a LAN
IPv4 forwarding
For a host to be able to forward IPv4 packets between the LAN and VPN, it must be able to forward the packets between its NIC and its tun/tap device.
Edit etc/sysctl.conf to permanently enable ipv4 packet forwarding (takes effect at the next boot):
/etc/sysctl.conf
# Enable packet forwarding net.ipv4.ip_forward=1
To temporarily enable without rebooting: # echo 1 > /proc/sys/net/ipv4/ip_forward
Promiscious LAN inteface
The forwarding host's NIC (eth0 in the following examples) must also be able to accept packets for a different IP address than it is configured for, something known as promiscious mode. To enable, add the following to /etc/rc.local (takes effect at the next boot):
/etc/rc.local
ip link set dev eth0 promisc on
To temporarily enable without rebooting: # ip link set dev eth0 promisc on
Routing tables
By default, all IP packets on a LAN addressed to a different subnet get sent to the default gateway. If the LAN/VPN gateway is also the default gateway, there is no problem and the packets get properly forwarded. If not, the gateway has no way of knowing where to send the packets. There are a couple of solutions to this problem.
- Add a static route to the default gateway routing the VPN subnet to the LAN/VPN gateway's IP address.
- Add a static route on each host on the LAN that needs to send IP packets back to the VPN.
- Use iptables' NAT feature on the LAN/VPN gateway to masquerade the incoming VPN IP packets.
Route a server side LAN to a client
Prerequisites:
- The server is on a LAN using the 10.66.0.0/24 private network range.
- The client is assigned an ip address out of the address pool 10.8.0.0/24.
/etc/openvpn/server.conf
server 10.8.0.0 255.255.255.0To inform the client about the available subnet, add a push directive to the server configuration file:
/etc/openvpn/server.conf
push "route 10.66.0.0 255.255.255.0"
To route more LANs from the server to the client, add more push directives to the server configuration file, but keep in mind that the server side LANs will need to know how to route to the client.
Route a client side LAN to a server
Prerequisites:
- Any subnets used on the client side, must be unique and not in use on the server or by any other client. In this example we will use 192.168.4.0/24 for the clients LAN.
- Each client's certificate has a unique Common Name, in this case bugs.
- The server may not use the duplicate-cn directive in its config file.
Create a client configuration directory on the server. It will be searched for a file named the same as the client's common name, and the directives will be applied to the client when it connects.
# mkdir -p /etc/openvpn/ccd
Create a file in the client configuration directory called bugs, containing the iroute 192.168.4.0 255.255.255.0 directive. It tells the server what subnet should be routed to the client:
/etc/openvpn/ccd/bugs
iroute 192.168.4.0 255.255.255.0
Add the client-config-dir and the route 192.168.4.0 255.255.255.0 directive to the server configuration file. It tells the server what subnet should be routed from the tun device to the server LAN:
/etc/openvpn/server.conf
client-config-dir ccd route 192.168.4.0 255.255.255.0
L2 Ethernet bridging
For now see: OpenVPN Bridge
Contributions that do not yet fit into the main article
Routing client traffic through the server
Append the following to your server's openvpn.conf configuration file:
push "redirect-gateway def1" push "dhcp-option DNS 192.168.1.1"
Change "192.168.1.1" to your preferred DNS IP address.
If you have problems with non responsive DNS after connecting to server, install BIND as simple DNS forwarder and push openvpn ip address of server as DNS to clients.
Configure ufw for routing
Configure your ufw settings to enable routing traffic from clients through server.
You must change default forward policy, edit /etc/sysctl.conf to permanently enable ipv4 packet forwarding. Takes effect at the next boot.
/etc/sysctl.conf
# Enable packet forwarding net.ipv4.ip_forward=1
And then configure ufw in /etc/default/ufw
/etc/default/ufw
DEFAULT_FORWARD_POLICY=”ACCEPT”
Now change /etc/ufw/before.rules, add following code after header and before *filter line, don't forget to change ip range to yours
/etc/ufw/before.rules
# nat Table rules *nat :POSTROUTING ACCEPT [0:0] # Allow traffic from clients to eth0 -A POSTROUTING -s 192.168.1.0/24 -o eth0 -j MASQUERADE # don.t delete the .COMMIT. line or these nat table rules won.t be processed COMMIT
Open openvpn port 1194
ufw allow 1194
usage of iptables
Use an iptable for NAT forwarding:
echo 1 > /proc/sys/net/ipv4/ip_forward iptables -t nat -A POSTROUTING -s 10.8.0.0/24 -o eth0 -j MASQUERADE
If running ArchLinux in a OpenVZ VPS environment [1]:
iptables -t nat -A POSTROUTING -s 10.8.0.0/24 -o venet0 -j SNAT --to (venet0 ip)
If all is well, make the changes permanent:
Edit /etc/conf.d/iptables and change IPTABLES_FORWARD=1
/etc/rc.d/iptables save
Configuring LDAP authorization
You may also want to install openvpn-authldap-pluginAUR, available in the Arch User Repository.
Deprecated older wiki content
Using PAM and passwords to authenticate
port 1194 proto udp dev tap ca /etc/openvpn/easy-rsa/keys/ca.crt cert /etc/openvpn/easy-rsa/keys/<MYSERVER>.crt key /etc/openvpn/easy-rsa/keys/<MYSERVER>.key dh /etc/openvpn/easy-rsa/keys/dh2048.pem server 192.168.56.0 255.255.255.0 ifconfig-pool-persist ipp.txt ;learn-address ./script client-to-client ;duplicate-cn keepalive 10 120 ;tls-auth ta.key 0 comp-lzo ;max-clients 100 ;user nobody ;group nobody persist-key persist-tun status /var/log/openvpn-status.log verb 3 client-cert-not-required username-as-common-name plugin /usr/lib/openvpn/openvpn-auth-pam.so login
Using certs to authenticate
port 1194 proto tcp dev tun0 ca /etc/openvpn/easy-rsa/keys/ca.crt cert /etc/openvpn/easy-rsa/keys/<MYSERVER>.crt key /etc/openvpn/easy-rsa/keys/<MYSERVER>.key dh /etc/openvpn/easy-rsa/keys/dh2048.pem server 10.8.0.0 255.255.255.0 ifconfig-pool-persist ipp.txt keepalive 10 120 comp-lzo user nobody group nobody persist-key persist-tun status /var/log/openvpn-status.log verb 3 log-append /var/log/openvpn status /tmp/vpn.status 10
Routing traffic through the server
Append the following to your server's openvpn.conf configuration file:
push "dhcp-option DNS 192.168.1.1" push "redirect-gateway def1"
Change "192.168.1.1" to your external DNS IP address.
Use an iptable for NAT forwarding:
echo 1 > /proc/sys/net/ipv4/ip_forward iptables -t nat -A POSTROUTING -s 10.8.0.0/24 -o eth0 -j MASQUERADE
If running ArchLinux in a OpenVZ VPS environment [2]:
iptables -t nat -A POSTROUTING -s 10.8.0.0/24 -o venet0 -j SNAT --to (venet0 ip)
If all is well, make the changes permanent:
Edit /etc/conf.d/iptables and change IPTABLES_FORWARD=1
/etc/rc.d/iptables save
Setting up the Client
The clientside .conf file
With password authentication
client dev tap proto udp remote <address> 1194 resolv-retry infinite nobind persist-tun comp-lzo verb 3 auth-user-pass passwd ca ca.crt
passwd file (referenced by auth-user-pass) must contain two lines:
- first line - username
- second - password
Certs authentication
client remote <MYSERVER> 1194 dev tun0 proto tcp resolv-retry infinite nobind persist-key persist-tun verb 2 ca ca.crt cert client1.crt key client1.key comp-lzo
Copy three files from server to remote computer.
ca.crt client1.crt client1.key
Install the tunnel/tap module:
# sudo modprobe tun
To have the tun module loaded automatically at boot time add it to the Modules line in /etc/rc.conf
DNS
The DNS servers used by the system are defined in /etc/resolv.conf. Traditionally, this file is the responsibility of whichever program deals with connecting the system to the network (e.g. Wicd, NetworkManager, etc...) However, OpenVPN will need to modify this file if you want to be able to resolve names on the remote side. To achieve this in a sensible way, install openresolv, which makes it possible for more than one program to modify resolv.conf without stepping on each-other's toes. Before continuing, test openresolv by restarting your network connection and ensuring that resolv.conf states that it was generated by "resolvconf", and that your DNS resolution still works as before. You should not need to configure openresolv; it should be automatically detected and used by your network system.
Next, save the following script at /usr/share/openvpn/update-resolv-conf:
#!/bin/bash
#
# Parses DHCP options from openvpn to update resolv.conf
# To use set as 'up' and 'down' script in your openvpn *.conf:
# up /etc/openvpn/update-resolv-conf
# down /etc/openvpn/update-resolv-conf
#
# Used snippets of resolvconf script by Thomas Hood <jdthood@yahoo.co.uk>
# and Chris Hanson
# Licensed under the GNU GPL. See /usr/share/common-licenses/GPL.
#
# 05/2006 chlauber@bnc.ch
#
# Example envs set from openvpn:
# foreign_option_1='dhcp-option DNS 193.43.27.132'
# foreign_option_2='dhcp-option DNS 193.43.27.133'
# foreign_option_3='dhcp-option DOMAIN be.bnc.ch'
[ -x /usr/sbin/resolvconf ] || exit 0
case $script_type in
up)
for optionname in ${!foreign_option_*} ; do
option="${!optionname}"
echo $option
part1=$(echo "$option" | cut -d " " -f 1)
if [ "$part1" == "dhcp-option" ] ; then
part2=$(echo "$option" | cut -d " " -f 2)
part3=$(echo "$option" | cut -d " " -f 3)
if [ "$part2" == "DNS" ] ; then
IF_DNS_NAMESERVERS="$IF_DNS_NAMESERVERS $part3"
fi
if [ "$part2" == "DOMAIN" ] ; then
IF_DNS_SEARCH="$part3"
fi
fi
done
R=""
if [ "$IF_DNS_SEARCH" ] ; then
R="${R}search $IF_DNS_SEARCH
"
fi
for NS in $IF_DNS_NAMESERVERS ; do
R="${R}nameserver $NS
"
done
echo -n "$R" | /usr/sbin/resolvconf -a "${dev}.inet"
;;
down)
/usr/sbin/resolvconf -d "${dev}.inet"
;;
esac
Remember to make the file executable with:
$ chmod +x /usr/share/openvpn/update-resolv-conf
Next, add the following lines to your OpenVPN client configuration file:
script-security 2 up /usr/share/openvpn/update-resolv-conf down /usr/share/openvpn/update-resolv-conf
Now, when your launch your OpenVPN connection, you should find that your resolv.conf file is updated accordingly, and also returns to normal when your close the connection.
Connecting to the Server
You need to start the service on the server
/etc/rc.d/openvpn start
You can add it to rc.conf to make it permanet.
On the client, in the home directory create a folder that will hold your OpenVPN client config files along with the .crt/.key files. Assuming your OpenVPN config folder is called .openvpn and your client config file is vpn1.conf, to connect to the server issue the following command:
cd ~/.openvpn && sudo openvpn vpn1.conf