Set Up OpenConnect VPN Server (ocserv) on Ubuntu 22.04 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 22.04. 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.

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
• Resistant to deep packet inspection (DPI)

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

Requirements

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 Kamatera VPS, which features:

• 30 days free trial.
• Starts at $4/month (1GB RAM)
• High-performance KVM-based VPS
• 9 data centers around the world, including United States, Canada, UK, Germany, The Netherlands, Hong Kong, and Isreal.

Follow the tutorial linked below to create your Linux VPS server at Kamatera.

• How to Create a Linux VPS Server on Kamatera

Once you have a VPS running Ubuntu 22.04, follow the instructions below.

You also need a domain name to enable HTTPS for OpenConnect VPN. I registered my domain name from NameCheap because the price is low and they give whois privacy protection free for life.

Step 1: Install OpenConnect VPN Server on Ubuntu 22.04

Log into your Ubuntu 22.04 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 22.04 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 1.21.0

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 22.04 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 [email protected] -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 22.04 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 [email protected] -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 [email protected] -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, find the following two lines.

tcp-port = 443
udp-port = 443

Comment out the UDP port. (We will use TCP BBR algorithm to boost TCP speed.)

tcp-port = 443 
#udp-port = 443

If you don’t want ocserv to use TCP port 443 (there’s a web server using port 443?), then change the TCP port number. Otherwise leave it alone.

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.

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

Find the following two lines and uncomment them, so VPN clients will be given private IPv6 addresses.

ipv6-network = fda9:4efe:7e3b:03ea::/48
ipv6-subnet-prefix = 64

If you see the following line

ipv6-network = fda9:4efe:7e3b:03ea::/64

Please change it to:

ipv6-network = fda9:4efe:7e3b:03ea::/48

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 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
#route = fd00::/8
#route = default

#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 by running the following command.

echo "net.ipv4.ip_forward = 1" | sudo tee /etc/sysctl.d/60-custom.conf

Also, run the following two commands to enable TCP BBR algorithm to boost TCP speed.

echo "net.core.default_qdisc=fq" | sudo tee -a /etc/sysctl.d/60-custom.conf

echo "net.ipv4.tcp_congestion_control=bbr" | sudo tee -a /etc/sysctl.d/60-custom.conf

Then apply the changes with the below command. The -p option will load sysctl settings from /etc/sysctl.d/60-custom.conf file. This command will preserve our changes across system reboots.

sudo sysctl -p /etc/sysctl.d/60-custom.conf

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

Step 9: Fix Futex Error

Run the following command to check the ocserv systemd journals.

sudo journalctl -eu ocserv

If your server has the following error, you need to install the latest ocserv version to fix the futex error.

The futex facility returned an unexpected error code.

Check your current ocserv version.

ocserv -v

Ubuntu 22.04 repository currently ships with ocserv 1.1.3. It might update ocserv in the future, but right now you need to follow the instructions below to install the latest ocserv version.

Install build dependency packages.

sudo apt install -y git ruby-ronn libbsd-dev libsystemd-dev libpcl-dev libwrap0-dev libgnutls28-dev libev-dev libpam0g-dev liblz4-dev libseccomp-dev libreadline-dev libnl-route-3-dev libkrb5-dev libradcli-dev libcurl4-gnutls-dev libcjose-dev libjansson-dev libprotobuf-c-dev libtalloc-dev libhttp-parser-dev protobuf-c-compiler gperf nuttcp lcov libuid-wrapper libpam-wrapper libnss-wrapper libsocket-wrapper gss-ntlmssp haproxy iputils-ping freeradius gawk gnutls-bin iproute2 yajl-tools tcpdump

Clone the ocserv Git repository.

git clone https://gitlab.com/openconnect/ocserv.git

Generate configuration scripts.

cd ocserv

autoreconf -fvi

Compile the source code. If you see deprecated warnings, you can ignore them.

./configure && make

Install the binaries.

sudo make install

The files will be install to /usr/loca/bin/ and /usr/local/sbin/. Next, we need to copy the systemd service file.

sudo cp /lib/systemd/system/ocserv.service /etc/systemd/system/ocserv.service

Edit this file.

sudo nano /etc/systemd/system/ocserv.service

Because the compiled version of ocserv binary is located at /usr/local/sbin/ocserv, we need to change

ExecStart=/usr/sbin/ocserv --foreground --pid-file /run/ocserv.pid --config /etc/ocserv/ocserv.conf

to

ExecStart=/usr/local/sbin/ocserv --foreground --pid-file /run/ocserv.pid --config /etc/ocserv/ocserv.conf

Save and close the file. Then reload systemd.

sudo systemctl daemon-reload

Restart ocserv service.

sudo systemctl restart ocserv

How to Install and Use OpenConnect VPN client on Ubuntu 22.04 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 the 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.

If you encounter the following error, then you should disable the UDP port in ocserv, which is explained later in the speed optimization section.

DTLS handshake failed: Resource temporarily unavailable, try again

If you have the following error, it’s likely that your VPN username or password is wrong.

fgets (stdin): Inappropriate ioctl for device

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.service and Wants=network-online.target make this service run after network is up. We want the openconnect.service start after the systemd-resolved.service because that will ensure the DNS server address set by OpenConnect won’t be overridden by systemd-resolved.service.
• In reality, this service can still run before network is up. We add Restart=always and RestartSec=2 to restart this service after 2 seconds if this service fails.
• Systemd doesn’t recognise pipe redirection, so in the ExecStart directive, 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 -b flag to the openconnect command.
• The KillSignal directive tells Systemd to send the SIGINT signal when the systemctl stop openconnect command 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.

• How to Easily boost Ubuntu Network Performance by enabling TCP BBR

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.

Also, check your CPU load average. (htop can be installed by sudo apt install htop).

htop

Make sure the CPU load average is under 1. I once had a CPU load average of 3, which caused a high latency between the VPN client and VPN server.

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.

0 5 * * * certbot renew --quiet && systemctl restart 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 Kamtera 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

Restart Your Computer

If you see the following error when trying to establish VPN connection, it’s likely a local computer problem. Try restarting your computer.

Server 'vpn.your-domain.com' requested Basic authentication which is disabled by default

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.

The local network may not be trustworthy

If you use the Cisco AnyConnect VPN client on iOS, and you encounter the following error, it’s likely your TLS certificate has expired.

If the TLS certificate has expired, you will also see the following error when trying to establish a VPN connection on a Linux desktop.

Server certificate verify failed: certificate expired
Certificate from VPN server "vpn.your-domain.com" failed verification.
Reason: certificate expired
To trust this server in future, perhaps add this to your command line:
     --servercert pin-sha256:er1Kv/37ZxHpN6VESmYVS7vw4wXEB1oYELwiBS2wcvc=
Enter 'yes' to accept, 'no' to abort; anything else to view: fgets (stdin): Operation now in progress

You will need to run the following command to renew TLS certificate.

sudo certbot renew --quiet

Don’t forget to restart ocserv.

sudo systemctl restart ocserv

If this error still persists after renewing the certificate, be sure to check the server-cert and server-key parameter in the /etc/ocserv/ocserv.conf file. Maybe it’s pointed to the wrong file.

No Tap-Windows Adapter installed on this system

If you use the OpenConnect GUI Windows client and found the “No Windows-TAP adapaters found” error in the logs (View – Log Window), this is likely because you have install other VPN clients afterward like OpenVPN.

To fix this error, you need to uninstall OpenConnect GUI client and reinstall it. In the setup wizard, you will have the option to install the TAP driver.

Two VPN Clients Share the Same Private IP Address?

I have an iPhone and iPad, and both of them use the AnyConnect VPN app to connect to ocserv VPN server, which is unable to tell the iPhone and iPad apart when they are in the same Wi-Fi network, so ocserv gives them the same private IP address, which causes the other unable to browse the Internet.

To fix this problem, I simply create two separate VPN accounts. One for iPhone and the other for iPad.

Make OpenConnect VPN server and web server use port 443 at the same time

Please read the following article:

• Run OpenConnect VPN Server & Apache/Nginx on the Same Box with HAProxy

More Useful Tips

• Ocserv Advanced (Split Tunneling, IPv6, Static IP, Per User Configs, Virtual Hosting)

Wrapping Up

That’s it! I hope this tutorial helped you install and configure OpenConnect VPN on Ubuntu 22.04. As always, if you found this post useful, then subscribe to our free newsletter to get more tips and tricks 🙂