Final answer:
Option (B), While the Wireless LAN Controller (WLC) is booting, the service port interface is the only available interface for management. It provides an out-of-band management capability and is critical during initial setup and troubleshooting processes when other interfaces are not accessible.
Step-by-step explanation:
The only interface available while the Wireless LAN Controller (WLC) is booting is the service port interface. This specialized interface is used for out-of-band management, allowing a network administrator to manage the WLC even when the normal management interfaces are not available, such as during the boot process. It provides a direct connection to the device for initial setup or for troubleshooting purposes when other interfaces can't be accessed.
Other interfaces like the management interface, AP manager interface, and virtual interface become operational only after the WLC has fully booted and is running its standard operating system software. The service port is typically connected to a network that is segregated from the rest of the network traffic, providing a secure management plane.