During the first registration, must be NIC eth0 (I have NIC eth1 and NIC eth2, Elastix, FOP2 - 2.25.2)?
It does not matter what NIC interface you use. The simplest one is to use eth0, as it is the one fop2 will default to use. If you need to use a different one for whatever reason, then you must indicate the nic name using the -i command line parameter, like
/usr/local/fop2/fop2_server --register -i em1
Once you do that, every time you invoke FOP2, you will need to remember to pass the same command line option if youu want it to recognize the license. You will also need to edit /etc/sysconfig/fop2 and add the parameter to the OPTIONS string defined there, so the init script will use it when you start/stop/restart.
Best regards,