OpenVPN

OpenVPN

For more information, see https://community.openvpn.net/.

Security note

The configuration snippets here will produce a working server and client config. But take certain precautions if you want to use this approach in a production environment. Important things to avoid are:

• Do not store the easy-rsa CA files on the OpenVPN server.
  • The server only needs ca.crt, server.crt, server.key and dh*.pem files
  • The client only needs ca.crt, client.crt and client.key
• Avoid creating the encryption keys in a virtualized environment, as the random entropy may not be random enough to guarantee safe keys.

Working with systemd

With the transition to systemd, OpenVPN no longer has a single monolithic init script, where every connection with a configuration file in /etc/openvpn/ is started automatically. Instead, individual connections can be started and stopped with systemctl.

For example, to start a connection, run systemctl start openvpn@foo.service, where the connection is defined in /etc/openvpn/foo.conf.

For more information, see Systemd#How_do_I_start.2Fstop_or_enable.2Fdisable_services.3F.

Setting up an OpenVPN server

1. yum install openvpn easy-rsa
2. Copy /usr/share/easy-rsa/2.0 somewhere (like root's home directory with cp -ai /usr/share/easy-rsa/2.0 ~/easy-rsa).
3. cd ~/easy-rsa
4. Edit vars appropriately.
5. . vars
6. ./clean-all
7. Before continuing, make sure the system time is correct. Preferably, set up NTP .
8. ./build-ca
9. ./build-key-server $( hostname | cut -d. -f1 )
10. ./build-dh
11. mkdir /etc/openvpn/keys
12. cp -ai keys/$( hostname | cut -d. -f1 ).{crt,key} keys/ca.crt keys/dh*.pem /etc/openvpn/keys/
13. cp -ai /usr/share/doc/openvpn*/sample/sample-config-files/roadwarrior-server.conf /etc/openvpn/server.conf
14. Edit /etc/openvpn/server.conf appropriately to set your configuration and key paths, which are found in /etc/openvpn/keys/.
15. Fix selinux context of files: restorecon -Rv /etc/openvpn
16. ln -s /lib/systemd/system/openvpn\@.service /etc/systemd/system/multi-user.target.wants/openvpn\@server.service (Note that 'server' corresponds with the configuration name in /etc/openvpn/ such as server.conf; that is, 'server' corresponds to whatever name your configuration file has)
17. systemctl -f enable openvpn@server.service
18. systemctl start openvpn@server.service
19. Verify that firewall rules allow traffic in from tun+, out from the LAN to tun+, and in from the outside on UDP port 1194.

The following should work (assuming an outside interface is eth1 and an inside interface is eth0):

iptables -A INPUT -i eth1 -p udp --dport 1194 -j ACCEPT
iptables -A INPUT -i tun+ -j ACCEPT
iptables -A FORWARD -i tun+ -j ACCEPT
iptables -A FORWARD -i eth0 -o tun+ -j ACCEPT
iptables -A FORWARD -i eth1 -o tun+ -m state --state ESTABLISHED,RELATED -j ACCEPT

Or for genfw (my firewall-generation script, not currently available in Fedora), this in /etc/sysconfig/genfw/rules:

append INPUT -i eth1 -p udp --dport 1194 -j ACCEPT
append INPUT -i tun+ -j ACCEPT
append FORWARD -i tun+ -j ACCEPT
append FORWARD -i eth0 -o tun+ -j ACCEPT
append FORWARD -i eth1 -o tun+ -j established

Or for system-config-firewall, you can add these custom rules:

-A INPUT -i eth1 -p udp --dport 1194 -j ACCEPT
-A INPUT -i tun+ -j ACCEPT
-A FORWARD -i tun+ -j ACCEPT
-A FORWARD -i eth0 -o tun+ -j ACCEPT
-A FORWARD -i eth1 -o tun+ -m state --state ESTABLISHED,RELATED -j ACCEPT

Create a file iptables-rules in /etc/sysconfig and add the above contents, then in system-config-firewall, choose the "Custom Rules" choice, click "Add", choose IPV4 for the protocol type, and filter for the firewall table. Then select /etc/sysconfig/iptables-rules for the File: choice. Then Apply the changes.

Setting up a Linux OpenVPN client

You need to generate new keys (or use existing other client/username keys) for the new client/username

On the server:

1. cd easy-rsa
2. . vars
3. ./build-key username

On the client:

• In the following, replace MyClient with a descriptive vpn connection name.

1. Copy username.key, username.crt and ca.crt from server to /etc/openvpn/keys/.
2. cp -ai /usr/share/doc/openvpn*/sample-config-files/client.conf /etc/openvpn/MyClient.conf
3. Edit /etc/openvpn/MyClient.conf appropriately to set your configuration (just like server configuration, port, compression,..) and key paths.
4. cd /lib/systemd/system
5. ln openvpn@.service openvpn@MyClient.service
6. systemctl enable openvpn@MyClient.service
7. systemctl start openvpn@MyClient.service

check /var/log/messages if things didn't work as expected

Alternatively, on the client, after copying the keys onto the client machine, you can use NetworkManager to add a vpn connection. Make sure you have the NetworkManager-openvpn package installed. Then just add a new VPN connection.

Should also test automatic starting at boot up, with password protected key files and maybe even --auth-user-pass. OpenVPN supports systemd's password passing if build with --enable-systemd via ./configure

Setting up a Windows OpenVPN client

On the server:

1. cd easy-rsa
2. . vars
3. ./build-key username

On the client:

1. Install the the OpenVPN Windows client.
2. Copy username.crt, username.key, and ca.crt to C:\Program Files\OpenVPN\config\ on the client.
3. Drop roadwarrior-client.conf into C:\Program Files\OpenVPN\config\ as whatever.ovpn and edit appropriately.
4. Either use the GUI to start the connection, start the OpenVPN service manually, or set the OpenVPN service to start automatically.

Ideally the client should do some verification on the server key with tls-remote in the whatever.ovpn configuration file.

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