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OpenVPN
OpenVPN (Open Virtual Private Network) is software that enables the creation of secure point-to-point or site-to-site connections.
Installation
Kernel
Device Drivers ---> [*] Network device support ---> [*] Network core driver support <*> Universal TUN/TAP device driver support
USE flags
USE flags for net-vpn/openvpn Robust and highly flexible tunneling application compatible with many OSes
+lz4
|
Enable support for lz4 compression (as implemented in app-arch/lz4) |
+lzo
|
Enable support for lzo compression |
+openssl
|
Use OpenSSL as the backend crypto library |
+plugins
|
Enable the OpenVPN plugin system |
dco
|
Enable support for kernel data channel offload |
down-root
|
Enable the down-root plugin |
examples
|
Install examples, usually source code |
inotify
|
Enable inotify filesystem monitoring support |
iproute2
|
Enabled iproute2 support instead of net-tools |
mbedtls
|
Use mbed TLS as the backend crypto library |
pam
|
Add support for PAM (Pluggable Authentication Modules) - DANGEROUS to arbitrarily flip |
pkcs11
|
Enable PKCS#11 smartcard support |
selinux
|
!!internal use only!! Security Enhanced Linux support, this must be set by the selinux profile or breakage will occur |
systemd
|
Enable use of systemd-specific libraries and features like socket activation or session tracking |
test
|
Enable dependencies and/or preparations necessary to run tests (usually controlled by FEATURES=test but can be toggled independently) |
Emerge
Install the OpenVPN package:
root #
emerge -v net-vpn/openvpn
Also consider installing net-dns/openresolv.
Configuration
Server side
If this is the first time setting up an openvpn server, we will need to create a PKI (Public Key Infrastructure) from scratch.
In this example place all generated keys into /etc/openvpn/example/
The example will just setup a single server. For multiple OpenVPN instances see the 'Gentoo specifics' section.
Write a server-side openvpn configuration.
# server binding port port 12112 # openvpn protocol, could be tcp / udp / tcp6 / udp6 proto udp # tun/tap device dev tun0 # keys configuration, use generated keys ca example/ca.crt cert example/example.crt key example/example.key dh example/dh2048.pem # optional tls-auth key to secure identifying # tls-auth example/ta.key 0 # OpenVPN 'virtual' network infomation, network and mask server 10.100.0.0 255.255.255.0 # persistent device and key settings persist-key persist-tun ifconfig-pool-persist ipp.txt # pushing route tables push "route 192.168.1.0 255.255.255.0" # push "dhcp-option DNS 192.168.1.1" # connection keepalive 10 120 comp-lzo user nobody group nobody # logging status openvpn-status.log log /etc/openvpn/openvpn.log verb 4
Start openvpn server, run
root #
/etc/init.d/openvpn start
Client side
Copy the necessary key files to client, via a secure way (such as SSH), including
- ca.crt
- client1.csr (in this example)
- client1.crt (in this example)
- client1.key (in this example)
- ta.key (if using tls-auth)
Write a client-side openvpn configuration file:
{{FileBox|filename=/etc/openvpn/openvpn.conf|title=client-side udp openvpn configuration|1=
- specify client-side
client
- tun/tap device
dev tun0
- protocol, according to server
proto udp
- server address
remote address.to.server 12112
- connection
comp-lzo resolv-retry 30 nobind
- persistent device and keys
persist-key persist-tun
- keys settings
ca example/ca.crt cert example/client1.crt key example/client1.key
- optional tls-auth
- tls-auth exmaple/ta.key 1
- pull dns settings from the server
script-security 2
- These scripts are defaults within the service script. To specify custom scripts,
- use /etc/openvpn/${SVCNAME}-{up,down}.sh as suggested by the service script.
- If you use systemd, SVCNAME will not get set automatically.
- Add `setenv SVCNAME my_svc_name` to set it, where my_svc_name is determined by
- /etc/openvpn/client/my_svc_name.conf
up /etc/openvpn/up.sh down /etc/openvpn/down.sh
- logging
log /etc/openvpn/openvpn.log verb 4}}
To automatically provide username and password, or just username with the password still prompted, add the following option, where auth is the file name containing 1 line with a username, or 2 lines with a username and password.
auth-user-pass /etc/openvpn/auth
To start client, run
OpenRC
root #
/etc/init.d/openvpn start
systemd
root #
systemctl start openvpn
If all goes well, this would give you a working OpenVPN server and client connection.
Monitoring
While the service is running, there are ways to monitor it.
Syslog
Assuming that syslog is enabled, OpenVPN's output is available, along with other services, on syslog.
Additionally, you can send signal to have it displaying status.
root #
killall -USR2 openvpn ; tail -f /var/log/syslog
This command does nothing but requesting statistic info. Nevertheless, be careful when using killall command!
Gentoo specifics
The init script allows multiple tunnels. Decide on a name for the tunnel - eg EXAMPLE
Using OpenRC
root #
ln -s /etc/init.d/openvpn /etc/init.d/openvpn.EXAMPLE
Now create your config as /etc/openvpn/EXAMPLE.conf
root #
/etc/init.d/openvpn.EXAMPLE start
Using systemd
Due to dependencies server and client operations are separated into two units.
Create your server config as /etc/openvpn/server/EXAMPLE.conf
root #
systemctl start openvpn-server@EXAMPLE
Create your client config as /etc/openvpn/client/EXAMPLE.conf
root #
systemctl start openvpn-client@EXAMPLE
You can then create more tunnels by replacing EXAMPLE with more names. Each one has its own configuration and can be stopped and started individually. The default is simply to use openvpn.conf and not symlink the service. You can of course use both methods.
Troubleshooting
/etc/resolv.conf doesn't get updated
Ensure that the option up and down on the configuration file points to the right path for the script.
Also, dhcpcd is known to overwrite pre-existing file when service is ran (e.g. either automatically called by other script, or manually called thru net-misc/netifrc).
In most cases, the conflict between different network programs can be resolved by installing net-dns/openresolv. The configuration would work out-of-box. Most networking scripts (including Gentoo's OpenVPN up & down script; along with dhcpcd) would regard its presence.
If disabling dhcpcd's resolv.conf update is necessary (most likely not), add the line below to /etc/dhcpcd.conf:
nohook resolv.conf