I have configured eth0 and eth2 as bond0, mode=4, and everything works until reboot. When everything comes back, it looks normal, put when I ping the computer, ping doesn't get the reply even though wireshark shows that it does. I remove the bond, reboot and reconfigure, everything works again. There are no error messages in /var/log/messages
More info….I installed CentOS 6 on the same machine, using a USB key, and after configuring found the same problem. narrowing it down, it seems that the second slave nic is not changing it's mac address to be the same as the bond or primary nics mac address. If I restart the network daemon, it then flips and the bond works.