Run script after interface up when using NetworkManager

Create a script as below in folder /etc/NetworkManager/dispatcher.d called 10-openvpn-tun0-up, change the permission to executable

#!/usr/bin/env bash

interface=$1
event=$2

if [[ $interface != "eth0" ]] || [[ $event != "up" ]]
then
  return 0
fi

# place your commands bellow this line

References

Network Manager script when interface up?