===== L2TP with IPSec VPN =====
  * On this example here is the case:
  - Eth1 connect to ISP (192.168.0.1/24)
  - Eth3 connect to Local Network (10.1.1.1/24)
  * First, create the L2TP server:

  PPP > Interface
  click L2TP server
  Enabled: checked
  Use IPsec: checked
  IPsec Secret: K@d3k&123 (example value)
  Click OK

  * Create the user:

  PPP > Secrets
  Name: vpnuser01 (example value)
  Password: P@ss&123 (example value)
  Service: l2tp
  Profile: vpn_profile
  Click OK