Using DHCP is most convenient process for setting up AP's interface IP & Master controller's IP address.
AP should have Master controller IP address eventhough AP get an IP address.
Setting up Master controller's IP address to each AP's is really annoying, furthermore sometimes the Master controller IP address could changed by any reason.
For the case, when AP have Master IP address manually, IT people have to take off whole APs from ceiling and connect serial cable for changing Master controller IP address.
ARUBA have very simple way to push Master controller IP address through DHCP option 43.
Here is the example of DHCP option 43 case and packet capture.
From the screen shot, 2b.04.ac.10.00.fc would be option 43 ip address.
If chaning each hexa value to decimal value,
Hexa : Decimal
2b = 43,
04 = 4,
ac = 172,
10 = 16,
00 = 0
fc = 254
so the meaning option 43, 4 length, 172.16.0.254
If you want to change the Master controller's IP addres to different one, just change IP address of option 43 in DHCP server and then reboot the whole AP and AP will change the Master IP from getting IP address from DHCP server.
Network Topology : Controller (172.16.0.254) ---- L3 Switch (126.96.36.199/24) ------ AP-105