Set Up OpenConnect VPN Server (ocserv) on Ubuntu 20.04 with Let’s Encrypt
This tutorial is going to show you how to run your own VPN server by installing OpenConnect VPN server on Ubuntu 20.04. OpenConnect VPN server, aka ocserv, is an open-source implementation of Cisco AnyConnnect VPN protocol, which is widely used in businesses and universities. AnyConnect is an SSL-based VPN protocol that allows individual users to connect to a remote network.
Note: This tutorial also works on Ubuntu 20.10 and Ubuntu 21.04.
Why Set Up Your Own VPN Server?
- Maybe you are a VPN service provider or a system administrator, which behooves you to set up our own VPN server.
- You don’t trust the no-logging policy of VPN service providers, so you go the self-host route.
- You can use VPN to implement network security policy. For example, if you run your own email server, you can require users to log in only from the IP address of the VPN server by creating an IP address whitelist in the firewall. Thus, your email server is hardened to prevent hacking activities.
- Perhaps you are just curious to know how VPN server works.
Features of OpenConnect VPN Server
- Lightweight and fast. In my test, I can watch YouTube 4K videos with OpenConnect VPN. YouTube is blocked in my country (China).
- Runs on Linux and most BSD servers.
- Compatible with Cisco AnyConnect client
- There are OpenConnect client software for Linux, MacOS, Windows and OpenWRT. For Android and iOS, you can use the Cisco AnyConnect Client.
- Supports password authentication and certificate authentication
- Supports RADIUS accounting.
- Supports virtual hosting (multiple domains).
- Easy to set up
I particularly like the fact that compared to other VPN technologies, it is very easy and convenient for the end-user to use OpenConnect VPN. Whenever I install a Linux distro on my computer and want to quickly unblock websites or hide my IP address, I install OpenConnect client and connect to the server with just two lines of commands:
sudo apt install openconnect sudo openconnect -b vpn.mydomain.com
There is also OpenConnect VPN client for Fedora, RHEL, CentOS, Arch Linux and OpenSUSE. You can easily install it with your package manager.
sudo dnf install openconnect sudo yum install openconnect sudo pacman -S openconnect
Prerequisites
To follow this tutorial, you will need a VPS (Virtual Private Server) that can access blocked websites freely (Outside of your country or Internet filtering system). I recommend Vultr VPS (This is my referral link. You can get $50 free credit by creating an account at Vultr via my referral link). They offer 512M memory high-performance KVM VPS for just $2.5 per month, which is perfect for your private VPN server. Once you have a VPS, install Ubuntu 20.04 on it and follow the instructions below.
You also need a domain name. I registered my domain name from NameCheap because the price is low and they give whois privacy protection free for life.
Update: The new Vultr $2.5/month plan includes IPv6 address only. You can select the $3.5/month plan at the New York (NJ) data center to have both IPv4 and IPv6 addresses.
Step 1: Install OpenConnect VPN Server on Ubuntu 20.04
Log into your Ubuntu 20.04 server. Then use apt to install the ocserv package from the default Ubuntu repository.
sudo apt update sudo apt install ocserv
Once installed, the OpenConnect VPN server is automatically started. You can check its status with:
systemctl status ocserv
Sample output:
● ocserv.service - OpenConnect SSL VPN server
Loaded: loaded (/lib/systemd/system/ocserv.service; enabled; vendor preset: enabled)
Active: active (running) since Sun 2020-04-12 19:57:08 HKT; 12s ago
Docs: man:ocserv(8)
Main PID: 216409 (ocserv-main)
Tasks: 2 (limit: 9451)
Memory: 1.6M
CGroup: /system.slice/ocserv.service
├─216409 ocserv-main
└─216429 ocserv-sm
Hint: If the above command doesn’t quit immediately, you can press the Q key to gain back control of the terminal.
If it’s not running, then you can start it with:
sudo systemctl start ocserv
By default OpenConnect VPN server listens on TCP and UDP port 443. If it’s being used by web server, then the VPN server would probably fail to start. We will see how to change the port in OpenConnect VPN configuration file later.
If there’s a firewall running on your server, then you will need to open port 80 and 443. For example, if you use UFW, then run the following command.
sudo ufw allow 80,443/tcp
Step 2: Install Let’s Encrypt Client (Certbot) on Ubuntu 20.04 Server
The gnutls-bin package installed along with ocserv provides tools to create your own CA and server certificate, but we will obtain and install Let’s Encrypt certificate. The advantage of using Let’s Encrypt certificate is that it’s free, easier to set up and trusted by VPN client software.
Run the following commands to install Let’s Encrypt client (certbot) from the default Ubuntu repository.
sudo apt install certbot
To check the version number, run
certbot --version
Sample output:
certbot 0.40.0
Step 3: Obtain a Trusted TLS Certificate from Let’s Encrypt
I recommend using the standalone or webroot plugin to obtain TLS certificate for ocserv.
Standalone Plugin
If there’s no web server running on your Ubuntu 20.04 server and you want OpenConnect VPN server to use port 443, then you can use the standalone plugin to obtain TLS certificate from Let’s Encrypt. Run the following command. Don’t forget to set A record for your domain name.
sudo certbot certonly --standalone --preferred-challenges http --agree-tos --email you@example.com -d vpn.example.com
Where:
certonly: Obtain a certificate but don’t install it.--standalone: Use the standalone plugin to obtain a certificate--preferred-challenges http: Perform http-01 challenge to validate our domain, which will use port 80.--agree-tos: Agree to Let’s Encrypt terms of service.--email: Email address is used for account registration and recovery.-d: Specify your domain name.
As you can see the from the following screenshot, I successfully obtained the certificate.
Using webroot Plugin
If your Ubuntu 20.04 server has a web server listening on port 80 and 443, then it’s a good idea to use the webroot plugin to obtain a certificate because the webroot plugin works with pretty much every web server and we don’t need to install the certificate in the web server.
First, you need to create a virtual host for vpn.example.com.
Apache
If you are using Apache, then
sudo nano /etc/apache2/sites-available/vpn.example.com.conf
And paste the following lines into the file.
<VirtualHost *:80>
ServerName vpn.example.com
DocumentRoot /var/www/ocserv
</VirtualHost>
Save and close the file. Then create the web root directory.
sudo mkdir /var/www/ocserv
Set www-data (Apache user) as the owner of the web root.
sudo chown www-data:www-data /var/www/ocserv -R
Enable this virtual host.
sudo a2ensite vpn.example.com
Reload Apache for the changes to take effect.
sudo systemctl reload apache2
Once virtual host is created and enabled, run the following command to obtain Let’s Encrypt certificate using webroot plugin.
sudo certbot certonly --webroot --agree-tos --email you@exmaple.com -d vpn.example.com -w /var/www/ocserv
Nginx
If you are using Nginx, then
sudo nano /etc/nginx/conf.d/vpn.example.com.conf
Paste the following lines into the file.
server {
listen 80;
server_name vpn.example.com;
root /var/www/ocserv/;
location ~ /.well-known/acme-challenge {
allow all;
}
}
Save and close the file. Then create the web root directory.
sudo mkdir -p /var/www/ocserv
Set www-data (Nginx user) as the owner of the web root.
sudo chown www-data:www-data /var/www/ocserv -R
Reload Nginx for the changes to take effect.
sudo systemctl reload nginx
Once virtual host is created and enabled, run the following command to obtain Let’s Encrypt certificate using webroot plugin.
sudo certbot certonly --webroot --agree-tos --email you@exmaple.com -d vpn.example.com -w /var/www/ocserv
Step 4: Edit OpenConnect VPN Server Configuration File
Edit ocserv main configuration file.
sudo nano /etc/ocserv/ocserv.conf
First, we need to configure password authentication. By default, password authentication through PAM (Pluggable Authentication Modules) is enabled, which allows you to use Ubuntu system accounts to login from VPN clients. This behavior can be disabled by commenting out the following line.
auth = "pam[gid-min=1000]"
If we want users to use separate VPN accounts instead of system accounts to login, we need to add the following line to enable password authentication with a password file.
auth = "plain[passwd=/etc/ocserv/ocpasswd]"
After finishing editing this config file, we will see how to use ocpasswd tool to generate the /etc/ocserv/ocpasswd file, which contains a list of usernames and encoded passwords.
Note: Ocserv supports client certificate authentication, but Let’s Encrypt does not issue client certificate. You need to set up your own CA to issue client certificate.
Next, if you don’t want ocserv to use TCP and UDP port 443, then find the following two lines and change the port number. Otherwise leave them alone.
tcp-port = 443 udp-port = 443
Then find the following two lines. We need to change them.
server-cert = /etc/ssl/certs/ssl-cert-snakeoil.pem server-key = /etc/ssl/private/ssl-cert-snakeoil.key
Replace the default setting with the path of Let’s Encrypt server certificate and server key file.
server-cert = /etc/letsencrypt/live/vpn.example.com/fullchain.pem server-key = /etc/letsencrypt/live/vpn.example.com/privkey.pem
Then, set the maximal number of clients. Default is 128. Set to zero for unlimited.
max-clients = 128
Set the number of devices a user is able to log in from at the same time. Default is 2. Set to zero for unlimited.
max-same-clients = 2
By default, keepalive packets are sent every 300 seconds (5 minutes). I prefer to use a short time (30 seconds) to reduce the chance of VPN connection dropout.
keepalive = 30
Next, find the following line. Change false to true to enable MTU discovery, which can optimize VPN performance.
try-mtu-discovery = false
You can set the time that a client is allowed to stay idle before being disconnected via the following two parameters. If you prefer the client to stay connected indefinitely, then comment out these two parameters.
idle-timeout=1200 mobile-idle-timeout=1800
After that, set the default domain to vpn.example.com.
default-domain = vpn.example.com
The IPv4 network configuration is as follows by default. This will cause problems because many home routers also set the IPv4 network range to 192.168.1.0/24.
ipv4-network = 192.168.1.0 ipv4-netmask = 255.255.255.0
We can use another private IP address range (10.10.10.0/24) to avoid IP address collision, so change the value of ipv4-network to
ipv4-network = 10.10.10.0
Now uncomment the following line to tunnel all DNS queries via the VPN.
tunnel-all-dns = true
The default DNS resolver addresses are as follows, which is fine.
dns = 8.8.8.8 dns = 1.1.1.1
Note: If you are a VPN service provider, then it’s a good practice to run your own DNS resolver on the same server. If there’s a DNS resolver running on the same server, then specify the DNS as
dns = 10.10.10.1
10.10.10.1 is the IP address of OpenConnect VPN server in the VPN LAN. This will speed up DNS lookups a little bit for clients because the network latency between the VPN server and the DNS resolver is eliminated.
Then comment out all the route parameters (add # symbol at the beginning of the following four lines), which will set the server as the default gateway for the clients.
route = 10.0.0.0/8 route = 172.16.0.0/12 route = 192.168.0.0/16 no-route = 192.168.5.0/255.255.255.0
Save and close the file Then restart the VPN server for the changes to take effect.
sudo systemctl restart ocserv
Step 5: Create VPN Accounts
Now use the ocpasswd tool to generate VPN accounts.
sudo ocpasswd -c /etc/ocserv/ocpasswd username
You will be asked to set a password for the user and the information will be saved to /etc/ocserv/ocpasswd file. To reset password, simply run the above command again.
Step 6: Enable IP Forwarding
In order for the VPN server to route packets between VPN clients and the Internet, we need to enable IP forwarding. Edit sysctl.conf file.
sudo nano /etc/sysctl.conf
Add the following line at the end of this file.
net.ipv4.ip_forward = 1
Save and close the file. Then apply the changes with the below command. The -p option will load sysctl settings from /etc/sysctl.conf file. This command will preserve our changes across system reboots.
sudo sysctl -p
Step 7: Configure IP Masquerading in Firewall
We need to set up IP masquerading in the server firewall, so that the server becomes a virtual router for VPN clients. I will use UFW, which is a front end to the iptables firewall. Install UFW on Ubuntu with:
sudo apt install ufw
First, you need to allow SSH traffic.
sudo ufw allow 22/tcp
Then find the name of your server’s main network interface.
ip addr
As you can see, it’s named ens3 on my Ubuntu server.
To configure IP masquerading, we have to add iptables command in a UFW configuration file.
sudo nano /etc/ufw/before.rules
By default, there are some rules for the filter table. Add the following lines at the end of this file. Replace ens3 with your own network interface name.
# NAT table rules *nat :POSTROUTING ACCEPT [0:0] -A POSTROUTING -s 10.10.10.0/24 -o ens3 -j MASQUERADE # End each table with the 'COMMIT' line or these rules won't be processed COMMIT
In Nano text editor, you can go to the end of the file by pressing Ctrl+W, then pressing Ctrl+V.
The above lines will append (-A) a rule to the end of of POSTROUTING chain of nat table. It will link your virtual private network with the Internet. And also hide your network from the outside world. So the Internet can only see your VPN server’s IP, but can’t see your VPN client’s IP, just like your home router hides your private home network.
By default, UFW forbids packet forwarding. We can allow forwarding for our private network. Find the ufw-before-forward chain in this file and add the following 3 lines, which will accept packet forwarding if the source IP or destination IP is in the 10.10.10.0/24 range.
# allow forwarding for trusted network -A ufw-before-forward -s 10.10.10.0/24 -j ACCEPT -A ufw-before-forward -d 10.10.10.0/24 -j ACCEPT
Save and close the file. Then enable UFW.
sudo ufw enable
If you have enabled UFW before, then you can use systemctl to restart UFW.
sudo systemctl restart ufw
Now if you list the rules in the POSTROUTING chain of the NAT table by using the following command:
sudo iptables -t nat -L POSTROUTING
You can see the Masquerade rule.
It can take some time for UFW to process the firewall rules. If the masquerade rule doesn’t show up, then restart UFW again (sudo systemctl restart ufw).
Step 8: Open Port 443 in Firewall
Run the following command to open TCP and UDP port 443. If you configured a different port for ocserv, then change 443 to your configured port.
sudo ufw allow 443/tcp sudo ufw allow 443/udp
Now OpenConnect VPN server is ready to accept client connections.
If you run a local DNS Resolver
For those of you who run a local DNS resolver, if you specified 10.10.10.1 as the DNS server for VPN clients, then you must allow VPN clients to connect to port 53 with the following UFW rule.
sudo ufw insert 1 allow in from 10.10.10.0/24
You also need to edit the BIND DNS server’s configuration file (/etc/bind/named.conf.options) to allow VPN clients to send recursive DNS queries like below.
allow-recursion { 127.0.0.1; 10.10.10.0/24; };
Then restart BIND.
sudo systemctl restart named
How to Install and Use OpenConnect VPN client on Ubuntu 20.04 Desktop
Run the following command to install OpenConnect VPN command line client on Ubuntu desktop.
sudo apt install openconnect
You can Connect to VPN from the command line like below. -b flag will make it run in the background after connection is established.
sudo openconnect -b vpn.example.com:port-number
You will be asked to enter VPN username and password. If connection is successfully established, you will see the following message.
Got CONNECT response: HTTP/1.1 200 CONNECTED CSTP connected. DPD 90, Keepalive 32400 Connected tun0 as 192.168.1.139, using SSL Established DTLS connection (using GnuTLS). Ciphersuite (DTLS1.2)-(RSA)-(AES-256-GCM).
To stop the connection, run:
sudo pkill openconnect
To run the client non-interactively, use the following syntax.
echo -n password | sudo openconnect -b vpn.example.com -u username --passwd-on-stdin
If you want to use Network Manager to manage VPN connection, then you also need to install these packages.
sudo apt install network-manager-openconnect network-manager-openconnect-gnome
If you are successfully connected to the VPN server, but your public IP address doesn’t change, that’s because IP forwarding or IP masquerading is not working. I once had a typo in my iptables command (using a wrong IP address range), which caused my computer not being able to browse the Internet.
Auto-Connect on System Startup
To let OpenConnect VPN client automatically connect to the server at boot time, we can create a systemd service unit.
sudo nano /etc/systemd/system/openconnect.service
Put the following lines to the file. Replace the red text.
[Unit] Description=OpenConnect VPN Client After=network-online.target systemd-resolved.service Wants=network-online.target [Service] Type=simple ExecStart=/bin/bash -c '/bin/echo -n password | /usr/sbin/openconnect vpn.example.com -u username --passwd-on-stdin' KillSignal=SIGINT Restart=always RestartSec=2 [Install] WantedBy=multi-user.target
Save and close the file. Then enable this service so that it will start at boot time.
sudo systemctl enable openconnect.service
Explanation of the file content:
After=network-online.target systemd-resolved.serviceandWants=network-online.targetmake this service run after network is up. We want theopenconnect.servicestart after thesystemd-resolved.servicebecause that will ensure the DNS server address set by OpenConnect won’t be overridden bysystemd-resolved.service.- In reality, this service can still run before network is up. We add
Restart=alwaysandRestartSec=2to restart this service after 2 seconds if this service fails. - Systemd doesn’t recognise pipe redirection, so in the
ExecStartdirective, we wrap the comand in single quotes and run it with the Bash shell. - Since OpenConnect VPN client will run as a systemd service, which runs in the background, there’s no need to add
-bflag to theopenconnectcommand. - The
KillSignaldirective tells Systemd to send theSIGINTsignal when thesystemctl stop openconnectcommand is issued. This will performs a clean shutdown by logging the session off, and restoring DNS server settings and the Linux kernel routing table.
To start this Systemd service immediately, run
sudo systemctl start openconnect
To stop this Systemd service, run
sudo systemctl stop openconnect
How to Automatically Restart OpenConnect Client When Resuming from Suspend
If your Ubuntu desktop goes into suspend state, the OpenConnect client would lose connection to the VPN server. To make it automatically restart when resuming from suspend, we need to create another systemd service unit.
sudo nano /etc/systemd/system/openconnect-restart.service
Add the following lines in the file.
[Unit] Description=Restart OpenConnect client when resuming from suspend After=suspend.target [Service] Type=simple ExecStart=/bin/systemctl --no-block restart openconnect.service [Install] WantedBy=suspend.target
Save and close the file. Then enable this service.
sudo systemctl enable openconnect-restart.service
Automatic-Restart When VPN Connection Drops
Sometimes the VPN connection would drop due to other reasons. You can run the following command to check if the VPN client can ping the VPN server’s private IP address (10.10.10.1). If the ping is unsuccessful, then the command on the right will be executed to restart the VPN client. || is the OR operator in Bash. It executes the command on the right only if the command on the left returned an error.
ping -c9 10.10.10.1 || systemctl restart openconnect
The ping will be done 9 times, i.e 9 seconds. You can use an infinite loop in the Bash shell to make the whole command run forever. Press Ctrl+C to stop it.
for ((; ; )) do (ping -c9 10.10.10.1 || systemctl restart openconnect) done
Now we can create a systemd service for this task.
sudo nano /etc/systemd/system/openconnect-check.service
Add the following lines to this file. We specify that this service should run after the openconnect.service.
[Unit] Description=OpenConnect VPN Connectivity Checker After=openconnect.service [Service] Type=simple ExecStart=/bin/bash -c 'for ((; ; )) do (ping -c9 10.10.10.1 || systemctl restart openconnect) done' [Install] WantedBy=multi-user.target
Save and close the file. Then start this service.
sudo systemctl start openconnect-check
Enable auto-start at boot time.
sudo systemctl enable openconnect-check
Once this service is started, the ping command will run forever. If the VPN connection drops, it will automatically restart openconnect.service.
OpenConnect GUI Client for Windows and macOS
They can be downloaded from OpenConnect GUI Github Page.
Speed
OpenConnect VPN is pretty fast. I can use it to watch 4k videos on YouTube. As you can see, my connection speed is 63356 Kbps, which translates to 61 Mbit/s.
And here’s the test results on speedtest.net.
Speed Optimization
OpenConnect by default uses TLS over UDP protocol (DTLS) to achieve faster speed, but UDP can’t provide reliable transmission. TCP is slower than UDP but can provide reliable transmission. One optimization tip I can give you is to disable DTLS, use standard TLS (over TCP), then enable TCP BBR to boost TCP speed.
To disable DTLS, comment out (add # symbol at the beginning) the following line in ocserv configuration file.
udp-port = 443
Save and close the file. Then restart ocserv service.
sudo systemctl restart ocserv.service
To enable TCP BBR, please check out the following tutorial. Note that you need to disable DTLS in ocserv, or TCP BBR won’t work.
In my test, standard TLS with TCP BBR enabled is two times faster than DTLS.
Another very important factor affecting speed is how good the connection between your local computer and the VPN server is. If you live in the middle east and the VPN server is located in the U.S, the speed would be slow. Choose a data center that’s close to where you live.
Auto-Renew Let’s Encrypt Certificate
Edit root user’s crontab file.
sudo crontab -e
Add the following line at the end of the file. It’s necessary to reload ocserv service for the VPN server to pick up new certificate and key file.
@daily certbot renew --quiet && systemctl reload ocserv
Troubleshooting Tips
OpenVZ
Note that if you are using OpenVZ VPS, make sure you enable the TUN virtual networking device in VPS control panel. (If you use Vultr VPS, then you have KVM-based VPS, so you don’t have to worry about this.)
Log File
If you encounter any problem, then check OpenConnect VPN server log.
sudo journalctl -eu ocserv.service
I found that if I change port 443 to a different port, the great firewall of China will block this VPN connection.
Debugging Mode
If ocserv tells you that it can’t load the /etc/ocserv/ocserv.conf file, you can stop ocserv.
sudo systemctl stop ocserv
Then run it in the foreground with debugging enabled.
sudo /usr/sbin/ocserv --foreground --pid-file /run/ocserv.pid --config /etc/ocserv/ocserv.conf --debug=10
Then output might give you some clues why ocserv isn’t working.
Can’t browse the Internet
If you are successfully connected to the VPN server, but you can’t browse the Internet, that’s because IP forwarding or IP masquerading is not working. I remember my VPS provider once did a platform upgrade, which changed the name of the main network interface from ens3 to enp3s0, so I had to update the name in the UFW file (/etc/ufw/before.rules).
Syntax Error
If you see the following error when trying to establish VPN connection, it’s probably because there’s a syntax error in your ocserv config file. Check the journal (sudo journalctl -eu ocserv) to find out.
Got inappropriate HTTP CONNECT response: HTTP/1.1 401 Cookie is not acceptable
TLS connection was non-properly terminated
If you see the following error on the client when trying to establish a VPN connection,
SSL connection failure: The TLS connection was non-properly terminated.
you probably should restart the ocserv service on the VPN server.
sudo systemctl restart ocserv
You can create a cron job to automatically restart ocserv once per day at 4 AM.
sudo crontab -e
Add the following line.
0 4 * * * systemctl restart ocserv
Save and close the file.
Make OpenConnect VPN server and web server use port 443 at the same time
Please read the following article:
How to Disable TLS 1.0 and TLS 1.1 in ocserv
The PCI council deprecated TLS 1.0 in June 30, 2018 and main stream web browsers are going to disable TLS 1.0 and TLS 1.1 in 2020. We should do the same with VPN server. Edit the main configuration file.
sudo nano /etc/ocserv/ocserv.conf
Find the following line:
tls-priorities = "NORMAL:%SERVER_PRECEDENCE:%COMPAT:-RSA:-VERS-SSL3.0:-ARCFOUR-128"
To disable TLS 1.0 and TLS 1.1 in OpenConnect VPN server, just add -VERS-TLS1.0 and -VERS-TLS1.1 in the line.
tls-priorities = "NORMAL:%SERVER_PRECEDENCE:%COMPAT:-RSA:-VERS-SSL3.0:-ARCFOUR-128:-VERS-TLS1.0:-VERS-TLS1.1"
Save and close the file. Then restart ocserv.
sudo systemctl restart ocserv
Now ocserv will only accept TLS 1.3 and TLS 1.2. For further information on configuring the TLS parameter in ocserv, please see GnuTLS priority strings.
To check if TLS 1.0 is supported in your OpenConnect VPN server, run the following command.
openssl s_client -connect vpn.your-domain.com:443 -tls1
And check TLS 1.1
openssl s_client -connect vpn.your-domain.com:443 -tls1_1
If you see the following message in the output, that means the TLS version is not supported.
New, (NONE), Cipher is (NONE) Secure Renegotiation IS NOT supported
Per-User or Per Group Configuration
Ocserv allows per user and per group configurations. To enable this feature, uncomment the following two lines in /etc/ocserv/ocserv.conf file.
config-per-user = /etc/ocserv/config-per-user/ config-per-group = /etc/ocserv/config-per-group/
Save and close the file. Then create the per user and per-group config directory.
sudo mkdir /etc/ocserv/config-per-user/ sudo mkdir /etc/ocserv/config-per-group/
Next, you can create a file under these two directories. For example, create the user1 file to allow custom configuration for user1.
sudo nano /etc/ocserv/config-per-user/user1
You can also create the group1 file to allow custom configuration for the group named group1.
sudo nano /etc/ocserv/config-per-group/group1
You can add something like below in the file to enable split tunneling.
route = 10.10.10.0/255.255.255.0 tunnel-all-dns = false dns = 8.8.8.8 dns = 1.1.1.1
Where:
- The first line means that after
user1or users ingroup1connect to this VPN server, only traffic to the10.10.10.0/24network will be routed via VPN server. Traffic to other IP addresses are routed via the original gateway. - The second line disables tunneling DNS queries.
- The third and fourth line set DNS servers for VPN clients.
I use this trick to allow my another VPS (virtual private server) to connect to this VPN server without disrupting normal traffic, so the TUN device (vpns0) of my VPN server is always turned on, which means my VPN server will always have the private IP address 10.10.10.1.
Save and close the file. Restart ocserv for the changes to take effect.
sudo systemctl restart ocserv
Note that if you enable IPv6 in ocserv, then you also need to add the IPv6 network range in order to use split tunneling.
route = 10.10.10.0/255.255.255.0 route = fda9:4efe:7e3b:03ea::/48 tunnel-all-dns = false dns = 8.8.8.8 dns = 1.1.1.1
If you want to exclude an IP address from the default route, then use no-route.
no-route = 12.34.56.78/32
This means all other traffic will go through the VPN tunnel except traffic to IP 12.34.56.78. route and no-route paramater accept both netmask notation (10.10.10.0/255.255.255.0) and CIDR notation (12.34.56.78/32)
If you see the following error after enabling split tunneling, it’s probably because you didn’t use the netmask or CIDR notation.
could not parse proxy protocol header; discarding connection
Split Tunneling by Country
Let’s say you only want traffic to foreign counties to be tunneled by the VPN. Traffic to your own country should use the normal route. You can use the no-route directive in ocserv configuration file to achieve this.
First, you need to download the IP range for your country by going to this web page: https://www.ip2location.com/free/visitor-blocker, which allows you to download the IP address range in CIDR format.
Save the IP range in a text file ip2location.txt, and run the following command in your Linux terminal to add the no-route = directive to the beginning of each line.
sed 's/^/no-route = /' -i ip2localtion.txt
Now open the file in a text editor and copy all the lines in it. We need to add these lines in the ocserv configuration file. If there are too many lines, you can and add these lines to the the per-user configuration file.
sudo nano /etc/ocserv/config-per-user/user1
You can also add them to the per-group configuration file, then add users to the group.
Restart ocserv for the changes to take effect.
sudo systemctl restart ocserv
How to Enable IPv6 in OpenConnect VPN
If your VPN server has a public IPv6 address, you can enable IPv6 in OpenConnect VPN. Edit ocserv configuariton file.
sudo nano /etc/ocserv/ocserv.conf
Find the following two lines and uncomment them.
ipv6-network = fda9:4efe:7e3b:03ea::/48 ipv6-subnet-prefix = 64
Save and close the file. Restart ocserv for the change to take effect.
sudo systemctl restart ocserv
Then we need to enable IP forwarding for IPv6. Edit sysctl.conf file.
sudo nano /etc/sysctl.conf
Add the following line at the end of this file.
net.ipv6.conf.all.forwarding=1
Save and close the file. Then apply the changes with the below command.
sudo sysctl -p
Next, we need to set up IPv6 masquerading in the server firewall, so that the server becomes a virtual router for VPN clients.
sudo nano /etc/ufw/before6.rules
By default, there are some rules for the filter table. Add the following lines at the end of this file. Replace ens3 with your own network interface name.
# NAT table rules *nat :POSTROUTING ACCEPT [0:0] -A POSTROUTING -o ens3 -j MASQUERADE # End each table with the 'COMMIT' line or these rules won't be processed COMMIT
In Nano text editor, you can go to the end of the file by pressing Ctrl+W, then pressing Ctrl+V.
By default, UFW forbids packet forwarding. We can allow forwarding for our private IPv6 network. Find the ufw6-before-forward chain in this file and add the following 3 lines, which will accept packet forwarding if the source IP or destination IP is in the fda9:4efe:7e3b:03ea::/48 range.
Save and close the file. Restart UFW for the change to take effect.
sudo systemctl restart ufw
Now if you list the rules in the POSTROUTING chain of the NAT table by using the following command:
sudo ip6tables -t nat -L POSTROUTING
You can see the Masquerade rule.
Disconnect the current VPN connection, add an AAAA record for vpn.example.com and re-establish VPN connection. Then go to https://test-ipv6.com/ to check your IPv6 connectivity.
If you run your own BIND DNS resolver on the VPN server, you can add the following line in /etc/ocserv/ocserv.conf file to set the VPN server as the DNS resolver for VPN clients.
dns = fda9:4efe:7e3b::1
Save and close the file. To query DNS names in IPv6, we need to configure BIND to allow IPv6 VPN clients.
sudo nano /etc/bind/named.conf.options
Find the allow-recursion parameter and change it to:
allow-recursion { 127.0.0.1; 10.10.10.0/24; fda9:4efe:7e3b:03ea::/48; };
Save and close the file. Restart BIND9.
sudo systemctl restart named
We also need to allow IPv6 VPN client in the firewall.
sudo ufw allow in from fda9:4efe:7e3b:03ea::/48
Virtual Hosting
Note: If you just want to have the ability to use multiple hostnames for the VPN server, you can use certbot to obtain a multi-domain certificate. Then restart ocserv and you are done.
To add a new virtual host in ocserv, first you need to use the method in step 3 to obtain a TLS certificate for the new virtual host. Then edit ocserv configuration file.
sudo nano /etc/ocserv/ocserv.conf
Go to the bottom of this file. In Nano text editor, you can press Ctrl+W, then Ctrl+V to jump to the bottom of a file. Add the following lines. Replace vpn2.example.com with the hostname of the second virtual host.
[vhost:vpn2.example.com] #Allow password authentication and certificate authentication enable-auth = "plain[passwd=/etc/ocserv/ocpasswd]" auth = "certificate" tcp-port = 443 #uncomment the two lines if ocserv runs behind HAProxy. #listen-host = 127.0.0.1 #listen-proxy-proto = true # SSL/TLS configuration ca-cert = /etc/ocserv/ssl/ca-cert.pem server-cert = /etc/letsencrypt/live/vpn2.example.com/fullchain.pem server-key = /etc/letsencrypt/live/vpn2.example.com/privkey.pem cert-user-oid = 0.9.2342.19200300.100.1.1 #Networking configuration. Use a different network range for this virtual host. device = vpns ipv4-network = 10.10.20.0 ipv4-netmask = 255.255.255.0 route = default dns = 8.8.8.8 tunnel-all-dns = true compression = true max-clients = 0 max-same-clients = 0 try-mtu-discovery = true idle-timeout=1200 mobile-idle-timeout=2400 config-per-user = /etc/ocserv/config-per-user/ config-per-group = /etc/ocserv/config-per-group/
Save and close the file. Then restart ocserv.
sudo systemctl restart ocserv
Edit the UFW configuration file.
sudo nano /etc/ufw/before.rules
Find the ufw-before-forward chain in this file and add the following 2 lines, which will accept packet forwarding if the source IP or destination IP is in the 10.10.20.0/24 range.
-A ufw-before-forward -s 10.10.20.0/24 -j ACCEPT -A ufw-before-forward -d 10.10.20.0/24 -j ACCEPT
Save and close the file. Then restart UFW.
sudo systemctl restart ufw
Note that the ocserv daemon might tell you some parameters will be ignored for virtual host. However, I found that some of the ignored parameters are actually needed. For example, if you delete the device = vpns line from the virtual host, you might encounter the following error when establishing VPN connection to the virtual host.
VPN service unavailable; reason: Server configuration error
And the VPN server would produce the following error message in the log.
no networks are configured; rejecting client
Also Note that the AnyConnect VPN client on iOS doesn’t support TLS SNI, so iOS users will connect to the default virtual host.
How to Run Multiple Instances of ocserv
One ocserv process can bind to only one TCP or UDP port on your server. If you want to allow ocserv to bind to multiple TCP or UDP ports, then you need to run multiple ocserv processes. It’s very simple. Copy the /lib/systemd/system/ocserv.service to a new file.
sudo cp /lib/systemd/system/ocserv.service /etc/systemd/system/ocserv2.service
Then edit the new file.
sudo nano /etc/systemd/system/ocserv2.service
Change
/etc/ocserv/ocserv.conf
to
/etc/ocserv/ocserv2.conf
Save and close the file. Next, you can edit the /etc/ocserv/ocserv2.conf file and add your custom configurations. Once you are done, start the second ocserv service.
sudo systemctl start ocserv2