Configuring a VPN Server

The following scenario walks through how to set up an IPsec or OpenVPN VPN server. Once a VPN server is configured, a secure connection can be established between an internal network and the production environment on DXP Cloud. This example uses Ubuntu Server 18.0.4 as a proof of concept. Please read the VPN Integration Overview article for an overview on DXP Cloud’s Client-to-Site VPNs functionality.


Configuration commands and values are subject to change and should be adapted for your specific environment.

EAP-TLS and EAP-MSCHAPV2 authentication protocols are both supported for VPN connections.

Basic Setup for an IPsec Server

To configure an IPsec test server:

  1. Save the following file as ~/ipsec.conf and replace the leftid value with your VPN server’s external IP.

    config setup
      charondebug="ike 1, knl 1, cfg 0"
    conn ikev2-vpn

    If you want to use the EAP-TLS protocol instead of only EAP-MSCHAPv2, add eap-tls to the rightauth line of the configuration:

  2. On your server, replace the SERVER_EXTERNAL_IP with your VPN server’s external IP and USERNAME/PASSWORD with your values:

  3. Install the necessary dependencies:

    sudo apt-get update
    sudo apt install -y strongswan strongswan-pki
    sudo apt install -y libstrongswan-extra-plugins
  4. Set up the security certificates and keys.

    If you want to use EAP-MSCHAPV2, then run these commands to generate the certificate:

    mkdir -p ~/pki/{cacerts,certs,private}
    chmod 700 ~/pki
    ipsec pki --gen --type rsa --size 4096 --outform pem > ~/pki/private/ca-key.pem
    ipsec pki --self --ca --lifetime 3650 --in ~/pki/private/ca-key.pem \ --type rsa --dn "CN=VPN root CA" --outform pem > ~/pki/cacerts/ca-cert.pem
    ipsec pki --gen --type rsa --size 4096 --outform pem > ~/pki/private/server-key.pem
    ipsec pki --pub --in ~/pki/private/server-key.pem --type rsa \
    |   ipsec pki --issue --lifetime 1825 \
      --cacert ~/pki/cacerts/ca-cert.pem \
      --cakey ~/pki/private/ca-key.pem \
      --flag serverAuth --flag ikeIntermediate --outform pem \
    >  ~/pki/certs/server-cert.pem
    sudo cp -r ~/pki/* /etc/ipsec.d/

    Otherwise, to use EAP-TLS, run these commands:

    mkdir -p ~/pki/certs
    chmod 700 ~/pki
    cd ~/pki/certs
    ipsec pki --gen --outform pem > caKey.pem
    ipsec pki --self --in caKey.pem --dn "CN=VPN CA" --ca --outform pem > caCert.pem
    openssl x509 -in caCert.pem -outform der | base64 -w0 ; echo
    export PASSWORD="password"
    export USER_NAME="client"
    ipsec pki --gen --outform pem > "${USER_NAME}Key.pem"
    ipsec pki --pub --in "${USER_NAME}Key.pem" \
    | ipsec pki --issue --cacert caCert.pem \
      --cakey caKey.pem \
      --dn "CN=${USER_NAME}" \
      --san "${USER_NAME}" \
      --flag clientAuth \
      --outform pem \
    > "${USER_NAME}Cert.pem"
    openssl pkcs12 -in "${USER_NAME}Cert.pem" \
      -inkey "${USER_NAME}Key.pem" \
      -certfile caCert.pem \
      -export -out "${USER_NAME}.p12" \
      -password "pass:${PASSWORD}"
    cd ..
    sudo cp -r ./certs/* /etc/ipsec.d/ 
  5. If you are using EAP-TLS for your VPN connection, then add this to your /etc/ipsec.secrets file (using your VPN password):

    : P12 client.p12 'password' # key filename inside /etc/ipsec.d/private directory
  6. Configure StrongSwan (see the server.conf file described above).

    sudo cp ~/ipsec.conf /etc/ipsec.conf
  7. Configure the VPN server’s authentication.

    echo -e ": RSA \"server-key.pem\"\n$USERNAME : EAP \"$PASSWORD\"" | sudo tee /etc/ipsec.secrets
    sudo systemctl restart strongswan
  8. Configure the OS kernel.

    sudo sed -i 's/#net\/ipv4\/ip_forward=1/net\/ipv4\/ip_forward=1/g' /etc/ufw/sysctl.conf
    sudo sed -i 's/#net\/ipv4\/conf\/all\/accept_redirects/net\/ipv4\/conf\/all\/accept_redirects/g' /etc/ufw/sysctl.conf
    echo "net/ipv4/conf/all/send_redirects=0" | sudo tee -a /etc/ufw/sysctl.conf
    echo "net/ipv4/ip_no_pmtu_disc=1" | sudo tee -a /etc/ufw/sysctl.conf
  9. Configure the OS’s firewall.

    networkInterfaceName=$(ip link | awk -F: '$0 !~ "lo|vir|^[^0-9]"{print $2a;getline}' | head -1)
    config="-A ufw-before-forward --match policy --pol ipsec --dir in --proto esp -s -j ACCEPT"
    config="$config\n-A ufw-before-forward --match policy --pol ipsec --dir out --proto esp -d -j ACCEPT"
    config="$config\n*nat\n-A POSTROUTING -s -o $networkInterfaceName -m policy --pol ipsec --dir out -j ACCEPT"
    config="$config\n-A POSTROUTING -s -o $networkInterfaceName -j MASQUERADE"
    config="$config\n-A FORWARD --match policy --pol ipsec --dir in -s -o $networkInterfaceName -p tcp -m tcp --tcp-flags SYN,RST SYN -m tcpmss --mss 1361:1536 -j TCPMSS --set-mss 1360"
    sudo sed -i "s/COMMIT//g" /etc/ufw/before.rules
    echo -e $config | sudo tee -a /etc/ufw/before.rules
    sudo ufw allow 500,4500/udp
    sudo ufw allow OpenSSH
    sudo ufw disable
    sudo ufw enable
  10. Obtain a server certificate to use on the client.

    cat /etc/ipsec.d/cacerts/ca-cert.pem

The IPsec VPN server has been configured.

Basic Setup for an OpenVPN Server

Follow these steps if using an OpenVPN server:

  1. Create a ~/server.conf with the following values:

    #Port where the VPN server will answer requests
    port 1194
    #TCP or UDP - UDP is faster
    proto udp
    #This will create a routed IP tunnel instead of an ethernet tunnel
    dev tun
    #The VPN subnet range, all IPs that connected clients will have upon connection
    #The Server will take the first IP (in this case,,
    #and all other addresses are available to clients
    #SSL root certificate (ca), certificate itself (cert) and private key (key)
    #All clients use the same CA, but have their own cert and key.
    ca /etc/openvpn/keys/ca.crt
    cert /etc/openvpn/keys/server.crt
    key /etc/openvpn/keys/server.key
    #Diffie Hellman parameters, this file can be generated with
    #openssl dhparam -out dh2048.pem 2048
    dh /etc/openvpn/keys/dh2048.pem
    #Records the IP address of each client so clients can use the same IP address
    #in case of reconnection
    ifconfig-pool-persist ipp.txt
    #Keeps connection alive, sends a ping every 10 seconds, and assume the connection is
    #down if no ping is received in 120 seconds
    keepalive 10 120
    #Cryptographic cipher used. The Client must use the same cipher
    cipher AES-256-CBC
    #HMAC - Hashed Message Authentication Code - used to avoid UDP port flooding,
    #must be the same on client and server
    auth SHA256
    #Enable compression on the VPN link
    compress lz4-v2
    push "compress lz4-v2"
    #Allows username/password authentication via PAM (linux accounts, LDAP),
    #if not provided, authentication is done via x509 certificates
    plugin /usr/lib/x86_64-linux-gnu/openvpn/plugins/ login
    #Explicitly disables x509 certificate authentication
    verify-client-cert none
    #Try to avoid accessing certain resources on restart,
    #since they may not be available
    #Notify all clients when the service is restarting,
    #so they can try to reconnect automatically
    explicit-exit-notify 1
    #Short status file showing current connections, updated every minute
    status openvpn-status.log
    #Redirect log messages to a log file
    log-append  /var/log/openvpn.log
    #Log verbosity, 0 is silent, 9 is extremely verbose
    verb 7
  2. Install the necessary dependencies:

    sudo apt-get update
    sudo apt-get install -y openvpn easy-rsa
  3. Set up the certificates and keys.

    make-cadir ~/openvpn-ca
    cd ~/openvpn-ca
    source vars
    ln -s openssl-1.0.0.cnf openssl.cnf
    ./build-key-server server
    openvpn --genkey --secret keys/ta.key
    sudo mkdir -p /etc/openvpn/keys/ && sudo cp ~/openvpn-ca/keys/* /etc/openvpn/keys/
  4. Use the OpenVPN server.conf file from above.

    sudo cp ~/server.conf /etc/openvpn/
  5. Configure the OS kernel.

    sudo sed -i 's/#net.ipv4.ip_forward=1/net.ipv4.ip_forward=1/g' /etc/sysctl.conf
    sudo sysctl -p
  6. Configure the OS firewall

    networkInterfaceName=$(ip link | awk -F: '$0 !~ "lo|vir|^[^0-9]"{print $2a;getline}' | head -1)
    echo -e "*nat\n:POSTROUTING ACCEPT [0:0]\n-A POSTROUTING -s -o $networkInterfaceName -j MASQUERADE\nCOMMIT\n" | sudo tee -a /etc/ufw/before.rules
    sudo sed -i 's/DEFAULT_FORWARD_POLICY="DROP"/DEFAULT_FORWARD_POLICY="ACCEPT"/g' /etc/default/ufw
    sudo ufw allow 1194/udp
    sudo ufw allow OpenSSH
    sudo ufw disable
    sudo ufw enable
  7. Start the VPN server service.

    sudo systemctl start [email protected]
  8. Create the OS user to be used for authentication on the VPN.

    sudo adduser myuser

The OpenVPN server has been configured.