[CentOS] Ethernet puzzle

> Remember, udev's rules lists FOUR devices.  There are only THREE.

>
> What does the BIOS say about ethernet devices?
>
> Does the motherboard have a management interface card with its own
> ethernet port, perhaps potential but not actually installed?
>
>

An IPMI may have its own MAC, but share a physical port with the main NIC.
If you are using this as a firewall, make sure to not have an IPMI port
facing the internet.

You may have a MAC address in one of your ifcfg-eth* files that does not
_exactly_ match the hardware.  Sometimes, it can be case-sensitive.
pushd /etc/sysconfig/network-scripts/
mkdir BACKUP
mv ifcfg-eth* ./BACKUP/
I would take out all the add-on cards and see if this extra MAC stays
around.
Put the other cards in one-by-one till found.