OK, this is what I did:
1. added the line to modprobe.conf, BTW, is it ok that eth1 and eth2 have the same alias?
2. the ifcfg-eth1 and ifcfg-eth2 already had MAC information. This are the files (in case you see something suspicious):
3. about your suggestion, i am a little confused about PPPoE and all that stuff, I'd tell you what I have in case you could help me. I am attaching an image of my modem internet configuration, it says "brigded mode", what does it mean? I have to change something in the server? please note that eth1 (the interface linked to the modem) is the one that is currently working.
One more thing, when I unplug the cable from eth1 i have no connection to the internet, it should start automatically working with eth2, right?, but it doesn't.
your help is much appreciated!