Hello what you need to do is a way of that AP 125 to find that Wireless controller
1-On your DNS server create a new record A with the name aruba-master and give it the IP address of the Wireless controller
2-On the vlan you are connecting the AP125 give it IP with DHCP and of course onthe dhcp server tell it that his primary dhcp server is your DNS server which you put the record A of aruba-master
3-At this point the AP should be able to communicate with the Controller
Be sure that the Vlan of the AP 125 can reach the IP of the wireless controller!
On the controller under configuration on the tab that it says control plane security before doing all that check if the CPsec is on or off
If its off then you have to do nothing... if it on be sure you have autocert enrollment so the AP can get his Cert automcatically... after you done provisioning the AP then click off the autcert enrollement
i hopte this helps you
Cheers
Carlos