via https://linuxfr.org/users/thomaselpozo/liens/les-vpn-gratuits
via https://www.reddit.com/r/Sysadmin_Fr/comments/a3npk2/installation_et_configuration_hautement_s%C3%A9curis%C3%A9e/
via @nixcraft
via @nixcraft via @linuxnewssite
pass in on $ext_if from $networkA to $networkB flags any keep state