Taking into account you have already a working Openvpn server, follow the steps bellow to configure static ip address to Openvpn users:
1. Create a folder called ccd inside /etc/openvpn/.
#mkdir /etc/openvpn/ccd
2. Add the following line to the openvpn server configuration file:
client-config-dir ccd
3. In /etc/openvpn/ccd/ you will create one file for each user you want to have [...]

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