To prevent the same MAC address from being allocated to different devices, one Logical Domains Manager checks with other Logical Domains Managers on other systems by sending a multicast message over the control domain's default network interface, including the address that the Logical Domain Manager wants to assign to the device. The Logical Domains Manger attempting to assign the MAC address waits for one second for a response back. If a different device on another LDoms-enabled system has already been assigned that MAC address, the Logical Domains Manager on that system sends back a response containing the MAC address in question. If the requesting Logical Domains Manager receives a response, it knows the chosen MAC address has already been allocated, chooses another, and iterates.
By default, these multicast messages are sent only to other managers on the same subnet; the default time-to-live (TTL) is 1. The TTL can be configured using the Service Management Facilities (SMF) property ldmd/hops.
Each Logical Domains Manager is responsible for:
Listening for multicast messages
Keeping track of MAC addresses assigned to its domains
Looking for duplicates
Responding so that duplicates do not occur
If the Logical Domains Manager on a system is shut down for any reason, duplicate MAC addresses could occur while the Logical Domains Manager is down.
Automatic MAC allocation occurs at the time the logical domain or network device is created and persists until the device or the logical domain is removed.