In order to automatically bring up (ifup) a NIC upon boot, as relevant configuration file should be modified.
It can be found under /etc/sysconfig/network-scripts - look for a file corresponding the name of the device - e.g. ifcfg-ens33 for a NIC named ens33.
At the end of the file, there's a line stating that "ONBOOT=no", meaning that the option we're looking for is disabled - just change "no" to "yes" and reboot - the NIC should be up after the reboot.
