Difference between revisions of "OpenVPN"
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[[Category:Virtual Private Network]] | [[Category:Virtual Private Network]] | ||
+ | [[de:OpenVPN]] | ||
[[zh-CN:OpenVPN]] | [[zh-CN:OpenVPN]] | ||
{{Expansion|(at least) add support for ipv6 and L2 ethernet bridging}} | {{Expansion|(at least) add support for ipv6 and L2 ethernet bridging}} | ||
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==Configure the system for TUN/TAP support== | ==Configure the system for TUN/TAP support== | ||
− | OpenVPN requires TUN/TAP support. Make sure to load the | + | OpenVPN requires TUN/TAP support. Make sure to load at boot the {{ic|tun}} module. |
− | {{ | + | Read [[Kernel Modules]] for more information. |
− | + | ||
− | + | The default kernel is already properly configured, but if you use another kernel make sure to enable the TUN/TAP module. If {{ic|$ zgrep CONFIG_TUN /proc/config.gz}} returns {{ic|<nowiki>CONFIG_TUN=n</nowiki>}}, make the following change to the kernel config file and rebuild the kernel. | |
+ | |||
+ | {{hc|Kernel config file| | ||
+ | Device Drivers | ||
+ | --> Network device support | ||
+ | [M] Universal TUN/TAP device driver support}} | ||
==Connect to a VPN provided by a third party== | ==Connect to a VPN provided by a third party== | ||
Line 106: | Line 112: | ||
Edit the following: | Edit the following: | ||
− | * The remote directive to reflect the server's [[Wikipedia:Fully qualified domain name|Fully Qualified Domain Name]] | + | * The remote directive to reflect either the server's [[Wikipedia:Fully qualified domain name|Fully Qualified Domain Name]] hostname (as known to the client) or its IP address. |
* Uncomment the user and group directives to drop privileges. | * 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. | * The ca, cert, and key parameters to reflect the path and names of the keys and certificates. | ||
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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 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 Diffie-Hellman initialized with 2048 bit key | ||
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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 14:41:54 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 PUSH: Received control message: 'PUSH_REQUEST' | ||
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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 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 LZO compression initialized | ||
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Wed Dec 28 14:41:57 2011 GID set to nobody | 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 UID set to nobody | ||
Line 215: | Line 162: | ||
{{hc|# ip addr show|<nowiki> | {{hc|# ip addr show|<nowiki> | ||
− | |||
. | . | ||
. | . | ||
Line 229: | Line 175: | ||
. | . | ||
. | . | ||
− | + | 37: tun0: <POINTOPOINT,MULTICAST,NOARP,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UNKNOWN qlen 100 | |
− | 37: | ||
link/none | link/none | ||
− | inet 10.8.0.6 peer 10.8.0.5/32 scope global | + | inet 10.8.0.6 peer 10.8.0.5/32 scope global tun0</nowiki>}} |
And the client side has been given the IP 10.8.0.6. | And the client side has been given the IP 10.8.0.6. | ||
Line 240: | Line 185: | ||
On the server: | On the server: | ||
− | {{hc|# ping 10.8.0.6|<nowiki> | + | {{hc|# ping -c3 10.8.0.6|<nowiki> |
PING 10.8.0.6 (10.8.0.6) 56(84) bytes of data. | 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=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=2 ttl=64 time=237 ms | ||
64 bytes from 10.8.0.6: icmp_req=3 ttl=64 time=205 ms | 64 bytes from 10.8.0.6: icmp_req=3 ttl=64 time=205 ms | ||
− | + | ||
--- 10.8.0.6 ping statistics --- | --- 10.8.0.6 ping statistics --- | ||
3 packets transmitted, 3 received, 0% packet loss, time 2002ms | 3 packets transmitted, 3 received, 0% packet loss, time 2002ms | ||
Line 253: | Line 198: | ||
On the client: | On the client: | ||
− | {{hc|# ping 10.8.0.1|<nowiki> | + | {{hc|# ping -c3 10.8.0.1|<nowiki> |
PING 10.8.0.1 (10.8.0.1) 56(84) bytes of data. | 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=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=2 ttl=64 time=158 ms | ||
64 bytes from 10.8.0.1: icmp_req=3 ttl=64 time=157 ms | 64 bytes from 10.8.0.1: icmp_req=3 ttl=64 time=157 ms | ||
− | + | ||
--- 10.8.0.1 ping statistics --- | --- 10.8.0.1 ping statistics --- | ||
3 packets transmitted, 3 received, 0% packet loss, time 2001ms | 3 packets transmitted, 3 received, 0% packet loss, time 2001ms | ||
Line 265: | Line 210: | ||
You now have a working OpenVPN installation, and your client (bugs) will be able to use services on the server (elmer), and vice versa. | You now have a working OpenVPN installation, and your client (bugs) will be able to use services on the server (elmer), and vice versa. | ||
+ | |||
+ | {{Note|If using a firewall, make sure that ip packets on the TUN device are not blocked.}} | ||
+ | |||
+ | ===Configure the MTU with Fragment and MSS=== | ||
+ | |||
+ | {{Note|If you do not configure MTU then you will notice that small packets like ping and DNS will work, however web browsing will not work.}} | ||
+ | |||
+ | Now it is time to configure the maximum segment size (MSS). In order to do this we need to discover what is the smallest MTU along the path between the client and server. In order to do this you can ping the server and disable fragmentation. Then specify the max packetsize. | ||
+ | |||
+ | {{hc|# ping -c5 -M do -s 1500 elmer.acmecorp.org|<nowiki> | ||
+ | PING elmer.acmecorp.org (99.88.77.66) 1500(1528) bytes of data. | ||
+ | From 1.2.3.4 (99.88.77.66) icmp_seq=1 Frag needed and DF set (mtu = 576) | ||
+ | From 1.2.3.4 (99.88.77.66) icmp_seq=1 Frag needed and DF set (mtu = 576) | ||
+ | From 1.2.3.4 (99.88.77.66) icmp_seq=1 Frag needed and DF set (mtu = 576) | ||
+ | From 1.2.3.4 (99.88.77.66) icmp_seq=1 Frag needed and DF set (mtu = 576) | ||
+ | From 1.2.3.4 (99.88.77.66) icmp_seq=1 Frag needed and DF set (mtu = 576) | ||
+ | |||
+ | --- core.myrelay.net ping statistics --- | ||
+ | 0 packets transmitted, 0 received, +5 errors | ||
+ | </nowiki>}} | ||
+ | |||
+ | We received an ICMP message telling us the MTU is 576 bytes. The means we need to fragment the UDP packets smaller then 576 bytes to allow for some UDP overhead. | ||
+ | |||
+ | {{hc|# ping -c5 -M do -s 548 elmer.acmecorp.org|<nowiki> | ||
+ | PING elmer.acmecorp.org (99.88.77.66) 548(576) bytes of data. | ||
+ | 556 bytes from 99.88.77.66: icmp_seq=1 ttl=48 time=206 ms | ||
+ | 556 bytes from 99.88.77.66: icmp_seq=2 ttl=48 time=224 ms | ||
+ | 556 bytes from 99.88.77.66: icmp_seq=3 ttl=48 time=206 ms | ||
+ | 556 bytes from 99.88.77.66: icmp_seq=4 ttl=48 time=207 ms | ||
+ | 556 bytes from 99.88.77.66: icmp_seq=5 ttl=48 time=208 ms | ||
+ | |||
+ | --- myrelay.net ping statistics --- | ||
+ | 5 packets transmitted, 5 received, 0% packet loss, time 4001ms | ||
+ | rtt min/avg/max/mdev = 206.027/210.603/224.158/6.832 ms | ||
+ | </nowiki>}} | ||
+ | |||
+ | After some trial and error..., we discover that we need to fragment packets on 548 bytes. In order to do this we specify this fragment size in the configuration and instruct OpenVPN to fix the Maximum Segment Size (MSS). | ||
+ | |||
+ | {{hc|/etc/openvpn/client.conf| | ||
+ | remote elmer.acmecorp.org 1194 | ||
+ | . | ||
+ | . | ||
+ | fragment 548 | ||
+ | mssfix | ||
+ | . | ||
+ | . | ||
+ | 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''' | ||
+ | }} | ||
+ | |||
+ | |||
+ | {{Note|This will add about 3min's to OpenVPN start time. It is advisable to configure the fragment size unless your client is a laptop that will be connecting over many different networks and the bottle neck is on the client side.}} | ||
+ | |||
+ | You can also allow OpenVPN to do this for you by having OpenVPN do the ping testing every time the client connects to the VPN. | ||
+ | {{hc|/etc/openvpn/client.conf| | ||
+ | remote elmer.acmecorp.org 1194 | ||
+ | . | ||
+ | . | ||
+ | mtu-test | ||
+ | . | ||
+ | . | ||
+ | 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''' | ||
+ | }} | ||
==Starting OpenVPN== | ==Starting OpenVPN== | ||
− | |||
− | + | ===Manual startup=== | |
− | To | + | To troubleshoot a vpn connection, start the daemon manually with: {{ic|# openvpn /etc/openvpn/client.conf}}. |
=== Systemd service configuration === | === Systemd service configuration === | ||
− | |||
− | |||
− | |||
− | |||
− | |||
− | |||
− | [ | + | To start openvpn automatically at system boot, [[Daemon|enable]] {{ic|openvpn@''<configuration>''.service}}. |
− | + | ||
− | + | For example, if the configuration file is {{ic|/etc/openvpn/client.conf}}, the service name is {{ic|openvpn@client.service}}. | |
− | |||
− | |||
− | |||
− | {{ | ||
− | |||
− | |||
− | |||
− | {{ | ||
− | |||
==Advanced L3 IP routing== | ==Advanced L3 IP routing== | ||
Line 311: | Line 320: | ||
To temporarily enable without rebooting: {{ic|# echo 1 > /proc/sys/net/ipv4/ip_forward}} | To temporarily enable without rebooting: {{ic|# echo 1 > /proc/sys/net/ipv4/ip_forward}} | ||
− | ==== | + | ====Promiscuous LAN interface==== |
− | + | ||
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 [[Wikipedia:Promiscuous_mode|promiscious mode]]. To enable, add the following to {{ic|/etc/rc.local}} (takes effect at the next boot): | 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 [[Wikipedia:Promiscuous_mode|promiscious mode]]. To enable, add the following to {{ic|/etc/rc.local}} (takes effect at the next boot): | ||
Line 318: | Line 327: | ||
To temporarily enable without rebooting: {{ic|# ip link set dev eth0 promisc on}} | To temporarily enable without rebooting: {{ic|# ip link set dev eth0 promisc on}} | ||
+ | |||
+ | To set the {{ic|eth0}} in promiscuous mode using systemd use [[ Systemd/Services#Set_network_interface_in_promiscuous_mode | this service file ]] and enable it using: | ||
+ | |||
+ | # systemctl enable promiscuous@eth0.service | ||
====Routing tables==== | ====Routing tables==== | ||
Line 329: | Line 342: | ||
* Use [[iptables]]' NAT feature on the LAN/VPN gateway to masquerade the incoming VPN IP packets. | * Use [[iptables]]' NAT feature on the LAN/VPN gateway to masquerade the incoming VPN IP packets. | ||
− | === | + | ===Connect the server LAN to a client=== |
The server is on a LAN using the 10.66.0.0/24 subnet. To inform the client about the available subnet, add a push directive to the server configuration file:{{hc|/etc/openvpn/server.conf|push "route 10.66.0.0 255.255.255.0"}} | The server is on a LAN using the 10.66.0.0/24 subnet. To inform the client about the available subnet, add a push directive to the server configuration file:{{hc|/etc/openvpn/server.conf|push "route 10.66.0.0 255.255.255.0"}} | ||
Line 337: | Line 350: | ||
{{Note|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.}} | {{Note|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.}} | ||
− | === | + | ===Connect the client LAN to a server=== |
Prerequisites: | Prerequisites: | ||
Line 362: | Line 375: | ||
{{Note|Remember to enable ipv4 forwarding and to make the LAN interface promiscuous on the client. Make sure the client LAN knows how to reach the VPN server.}} | {{Note|Remember to enable ipv4 forwarding and to make the LAN interface promiscuous on the client. Make sure the client LAN knows how to reach the VPN server.}} | ||
− | {{Note| To route more LANs from the client to the server, add more iroute and route directives to the appropriate configuration files, but keep in mind that the client side LANs will need to know how to route to the server.}} | + | {{Note|To route more LANs from the client to the server, add more iroute and route directives to the appropriate configuration files, but keep in mind that the client side LANs will need to know how to route to the server.}} |
+ | |||
+ | ===Connect both the client and server LANs=== | ||
+ | |||
+ | Combine the two previous sections: | ||
+ | |||
+ | {{hc|/etc/openvpn/server.conf| | ||
+ | push "route 10.66.0.0 255.255.255.0" | ||
+ | . | ||
+ | . | ||
+ | client-config-dir ccd | ||
+ | route 192.168.4.0 255.255.255.0 | ||
+ | }} | ||
+ | |||
+ | |||
+ | {{hc|/etc/openvpn/ccd/bugs|iroute 192.168.4.0 255.255.255.0}} | ||
+ | |||
+ | |||
+ | {{Note|Remember to enable ipv4 forwarding and to make the LAN interfaces promiscuous on both the client and the server. Make sure that all the LANs or the needed hosts can route to all the destinations.}} | ||
+ | |||
+ | ===Connect clients and client LANs=== | ||
+ | |||
+ | By default clients will not see each other, to allow ip packets to flow between clients and/or client LANs add a client-to-client directive to the server configuration file: {{hc|/etc/openvpn/server.conf|client-to-client}} | ||
+ | |||
+ | In order for another client or client LAN to see a specific client LAN you will need to add a push directive for each client subnet to the server configuration file (this will make the server announce the available subnet(s) to other clients): | ||
+ | |||
+ | {{hc|/etc/openvpn/server.conf| | ||
+ | client-to-client | ||
+ | push "route 192.168.4.0 255.255.255.0" | ||
+ | push "route 192.168.5.0 255.255.255.0" | ||
+ | . | ||
+ | . | ||
+ | }} | ||
+ | |||
+ | {{Note|As always, make sure that the routing is properly configured.}} | ||
==L2 Ethernet bridging== | ==L2 Ethernet bridging== | ||
Line 397: | Line 444: | ||
{{hc|/etc/default/ufw|<nowiki> | {{hc|/etc/default/ufw|<nowiki> | ||
− | DEFAULT_FORWARD_POLICY= | + | DEFAULT_FORWARD_POLICY="ACCEPT" |
</nowiki>}} | </nowiki>}} | ||
− | Now change '''/etc/ufw/before.rules''', add following code after header and before *filter line | + | Now change '''/etc/ufw/before.rules''', and add the following code after the header and before the "*filter" line. Don't forget to change the IP/subnet mask to match the one in '''/etc/openvpn/server.conf'''. |
{{hc|/etc/ufw/before.rules|<nowiki> | {{hc|/etc/ufw/before.rules|<nowiki> | ||
− | # | + | # NAT (Network Address Translation) table rules |
*nat | *nat | ||
:POSTROUTING ACCEPT [0:0] | :POSTROUTING ACCEPT [0:0] | ||
# Allow traffic from clients to eth0 | # Allow traffic from clients to eth0 | ||
− | -A POSTROUTING -s | + | -A POSTROUTING -s 10.8.0.0/8 -o eth0 -j MASQUERADE |
− | # don | + | # don't delete the "COMMIT" line or the NAT table rules above won't be processed |
COMMIT | COMMIT | ||
</nowiki>}} | </nowiki>}} | ||
Line 420: | Line 467: | ||
}} | }} | ||
− | ==== | + | ====Using iptables==== |
Use an iptable for NAT forwarding: | Use an iptable for NAT forwarding: | ||
Line 435: | Line 482: | ||
If all is well, make the changes permanent: | If all is well, make the changes permanent: | ||
− | Edit /etc/conf.d/iptables and change IPTABLES_FORWARD=1 | + | Edit '''/etc/conf.d/iptables''' and change IPTABLES_FORWARD=1 |
{{bc| | {{bc| | ||
Line 455: | Line 502: | ||
port 1194 | port 1194 | ||
proto udp | proto udp | ||
+ | mtu-test | ||
dev tap | dev tap | ||
ca /etc/openvpn/easy-rsa/keys/ca.crt | ca /etc/openvpn/easy-rsa/keys/ca.crt | ||
Line 541: | Line 589: | ||
dev tap | dev tap | ||
proto udp | proto udp | ||
+ | mtu-test | ||
remote <address> 1194 | remote <address> 1194 | ||
resolv-retry infinite | resolv-retry infinite | ||
Line 622: | Line 671: | ||
fi | fi | ||
if [ "$part2" == "DOMAIN" ] ; then | if [ "$part2" == "DOMAIN" ] ; then | ||
− | IF_DNS_SEARCH="$part3" | + | IF_DNS_SEARCH="$IF_DNS_SEARCH $part3" |
fi | fi | ||
fi | fi | ||
Line 653: | Line 702: | ||
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. | 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. | ||
+ | |||
+ | =====Webmin===== | ||
+ | |||
+ | {{AUR|webmin-plugin-openvpn}} is available in the [[AUR]]. | ||
+ | {{Note|You must add "openvpn" to the end of /etc/webmin/webmin.acl.}} | ||
====Connecting to the Server==== | ====Connecting to the Server==== | ||
Line 659: | Line 713: | ||
/etc/rc.d/openvpn start | /etc/rc.d/openvpn start | ||
}} | }} | ||
− | You can add it to rc.conf to make it | + | You can add it to rc.conf to make it permanent. |
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: | 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: |
Revision as of 10:10, 20 April 2013
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 at boot the tun
module.
Read Kernel Modules for more information.
The default kernel is already properly configured, but if you use another kernel make sure to enable the TUN/TAP module. If $ zgrep CONFIG_TUN /proc/config.gz
returns CONFIG_TUN=n
, make the following change to the kernel config file and rebuild the kernel.
Kernel config file
Device Drivers --> Network device support [M] Universal TUN/TAP device driver support
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 either the server's Fully Qualified Domain Name hostname (as known to the client) or its 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 14:41:54 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 14:41:57 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: tun0: <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 tun0
And the client side has been given the IP 10.8.0.6.
Now try pinging the interfaces.
On the server:
# ping -c3 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 --- 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 -c3 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 --- 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.
Configure the MTU with Fragment and MSS
Now it is time to configure the maximum segment size (MSS). In order to do this we need to discover what is the smallest MTU along the path between the client and server. In order to do this you can ping the server and disable fragmentation. Then specify the max packetsize.
# ping -c5 -M do -s 1500 elmer.acmecorp.org
PING elmer.acmecorp.org (99.88.77.66) 1500(1528) bytes of data. From 1.2.3.4 (99.88.77.66) icmp_seq=1 Frag needed and DF set (mtu = 576) From 1.2.3.4 (99.88.77.66) icmp_seq=1 Frag needed and DF set (mtu = 576) From 1.2.3.4 (99.88.77.66) icmp_seq=1 Frag needed and DF set (mtu = 576) From 1.2.3.4 (99.88.77.66) icmp_seq=1 Frag needed and DF set (mtu = 576) From 1.2.3.4 (99.88.77.66) icmp_seq=1 Frag needed and DF set (mtu = 576) --- core.myrelay.net ping statistics --- 0 packets transmitted, 0 received, +5 errors
We received an ICMP message telling us the MTU is 576 bytes. The means we need to fragment the UDP packets smaller then 576 bytes to allow for some UDP overhead.
# ping -c5 -M do -s 548 elmer.acmecorp.org
PING elmer.acmecorp.org (99.88.77.66) 548(576) bytes of data. 556 bytes from 99.88.77.66: icmp_seq=1 ttl=48 time=206 ms 556 bytes from 99.88.77.66: icmp_seq=2 ttl=48 time=224 ms 556 bytes from 99.88.77.66: icmp_seq=3 ttl=48 time=206 ms 556 bytes from 99.88.77.66: icmp_seq=4 ttl=48 time=207 ms 556 bytes from 99.88.77.66: icmp_seq=5 ttl=48 time=208 ms --- myrelay.net ping statistics --- 5 packets transmitted, 5 received, 0% packet loss, time 4001ms rtt min/avg/max/mdev = 206.027/210.603/224.158/6.832 ms
After some trial and error..., we discover that we need to fragment packets on 548 bytes. In order to do this we specify this fragment size in the configuration and instruct OpenVPN to fix the Maximum Segment Size (MSS).
/etc/openvpn/client.conf
remote elmer.acmecorp.org 1194 . . fragment 548 mssfix . . 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
You can also allow OpenVPN to do this for you by having OpenVPN do the ping testing every time the client connects to the VPN.
/etc/openvpn/client.conf
remote elmer.acmecorp.org 1194 . . mtu-test . . 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
Starting OpenVPN
Manual startup
To troubleshoot a vpn connection, start the daemon manually with: # openvpn /etc/openvpn/client.conf
.
Systemd service configuration
To start openvpn automatically at system boot, enable openvpn@<configuration>.service
.
For example, if the configuration file is /etc/openvpn/client.conf
, the service name is openvpn@client.service
.
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
Promiscuous LAN interface
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
To set the eth0
in promiscuous mode using systemd use this service file and enable it using:
# systemctl enable promiscuous@eth0.service
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.
Connect the server LAN to a client
The server is on a LAN using the 10.66.0.0/24 subnet. To 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"
Connect the client 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
Connect both the client and server LANs
Combine the two previous sections:
/etc/openvpn/server.conf
push "route 10.66.0.0 255.255.255.0" . . client-config-dir ccd route 192.168.4.0 255.255.255.0
/etc/openvpn/ccd/bugs
iroute 192.168.4.0 255.255.255.0
Connect clients and client LANs
By default clients will not see each other, to allow ip packets to flow between clients and/or client LANs add a client-to-client directive to the server configuration file:/etc/openvpn/server.conf
client-to-client
In order for another client or client LAN to see a specific client LAN you will need to add a push directive for each client subnet to the server configuration file (this will make the server announce the available subnet(s) to other clients):
/etc/openvpn/server.conf
client-to-client push "route 192.168.4.0 255.255.255.0" push "route 192.168.5.0 255.255.255.0" . .
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, and add the following code after the header and before the "*filter" line. Don't forget to change the IP/subnet mask to match the one in /etc/openvpn/server.conf.
/etc/ufw/before.rules
# NAT (Network Address Translation) table rules *nat :POSTROUTING ACCEPT [0:0] # Allow traffic from clients to eth0 -A POSTROUTING -s 10.8.0.0/8 -o eth0 -j MASQUERADE # don't delete the "COMMIT" line or the NAT table rules above won't be processed COMMIT
Open openvpn port 1194
ufw allow 1194
Using 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 mtu-test 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 mtu-test 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="$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.
Webmin
webmin-plugin-openvpnAUR is available in the AUR.
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 permanent.
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