Product and Software: This article applies to all Aruba controllers and ArubaOS versions.
For a controller to communicate with rest of the network, only an IP interface associated to a VLAN is needed. A loopback interface is not a must. On the other hand, it is not advisable to have a loopback(or management address) and no IP interface associated to any of the VLANs. When you use the loopback interface, assign a routable IP from one of the VLANs local to the controller.
You can use loopback interface for sourcing the traffic from the controller.
(A200)(config) #ip radius source-interface loopback
Here is how you would configure the loopback address:
(A200) (config) #show ip interface b
Interface IP Address / IP Netmask Admin Protocol
vlan 1 172.16.0.254 / 255.255.255.0 up down
vlan 400 10.168.123.186 / 255.255.248.0 up up
loopback 10.168.123.185 / 255.255.255.255 up up