When an agent communicates with the ePO server, the server first checks whether the agent's GUID exists in the database:

• If the agent's GUID exists, ePO already knows this system and doesn’t need to add it to the database again.
• If the agent's GUID doesn’t exist, this computer is either new, or the GUID has been changed. For example, it changed during a complete reinstallation of the agent.

To differentiate between these cases when the GUID is unknown, the server performs another step. The additional step checks whether the MAC address is already known. If it is, the ePO server assumes that the computer's GUID changed. It then associates the new GUID with the database entry that contains the matching MAC address. But, this action causes problems when multiple computers legitimately have the same MAC address. For example, in a Network Load-Balancing scenario, or with teamed NICs.

In this situation, the first node to communicate is added to the database correctly. But, when the second node communicates, its properties replace those properties of the first node because it has a new GUID, but the same MAC address. When the first node communicates again, its properties replace the properties of the second node. The result is that only one node displays in ePO at any one time.