Due to the fact that /etc/modprobe.conf has been deprecated in RHEL 6, the process of bonding network interfaces has changed a bit.
Now instead of defining your bond in your /etc/modprobe.conf, you define it in /etc/modprobe.d/bonding.conf. No changes in syntax.
alias bond0 bonding
Then in your ifconfig-bond0 file, you define your bonding mode. Note the quotes, and the fact that I explicitly typed out the bonding mode.