Which discovery method comes last in the AP's search for the Master Controller?

The correct answer is the DNS query because it is typically the final method in the search process for an Aruba Master Controller by an Access Point (AP). In the typical sequence of discovery methods, the Access Point will first attempt to locate the Master Controller using methods that do not rely on existing infrastructure.

Initially, the AP will use ADP (Aruba Discovery Protocol) multicast to send discovery requests across the network. If that fails, it will then try ADP broadcast which is similar but operates in a different network segment. DHCP option 43 can also be utilized as a means to provide the AP with the IP address of the Master Controller if the AP has obtained its IP address via DHCP.

However, the DNS query is considered last in this sequence as it relies on an external name resolution system and is implemented in scenarios where the previous methods did not yield a result. This makes it the least direct and typically the final attempt when determining the Master Controller address after utilizing local network-based discovery methods.