I have received many questions about how the Cisco Application Control Engine allocates MAC addresses. MAC addresses are used for physical interfaces, alias IP addresses, NAT, and VIP addresses. The default way in which the handles MAC addresses may lead to problems if the ACE is used in redundant mode, or if you have many ACE pairs on a common VLAN or subnet. When configuring and troubleshooting the ACE, it helps to have an understanding of the way that the ACE handles MAC addresses for its various interface types. In this document, I go over the various MAC addresses, and how to configure the ACE to avoid some of challenges that some have experienced.
General understanding of ACE hardware and software versions.